Nanotechnology Applied to the Conservation and Restoration of Pre-Hispanic Cultural Heritage

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(3) Contents! 3.2!Acrylic!resins! ! ! ! 3.2.1!Paraloid!B72©! ! ! 3.2.2!Primal!AC33©!! ! ! 3.3!Polyvinyl!acetate!resins! ! ! 3.4!Styrene!acrylate!resins! ! ! 3.4.1!Sokrat!2802A©! ! ! 3.5!DuPont!Products! ! ! ! 3.5.1!Nitrocellulose!lacquers! ! 3.5.2!Alkyd!resins!! ! ! 3.6!Polymers!degradation! ! ! ! Chapter'4'–'Detergent'Systems' ' 4.1!Introduction! ! ! ! 4.2!Surfactants!! ! ! ! 4.2.1!Surfactants!classification! ! 4.3!Micellar!solutions! ! ! ! 4.4!Emulsions!–!Microemulsions! ! 4.4.1!Emulsions! ! ! ! 4.4.2!Microemulsions! ! ! 4.5!Detergency!properties! ! ! 4.6!Detergent!systems!versus!solvents! !. ! ! ! ! ! ! ! ! ! !. ! ! ! ! ! ! ! ! ! !. !!!!!!!!!!!!!!22! !!!!!!!!!!!!!!23! !!!!!!!!!!!!!!24! !!!!!!!!!!!!!!24! !!!!!!!!!!!!!!26! !!!!!!!!!!!!!!26! !!!!!!!!!!!!!!27! !!!!!!!!!!!!!!28! !!!!!!!!!!!!!!28! !!!!!!!!!!!!!!29!. ' ! ! ! ! ! ! ! ! !. ' ! ! ! ! ! ! ! ! !. ' ! ! ! ! ! ! ! ! !. 33' 33! 34! 35! 36! 38!! 39! 39! 41! 41!. ' ! ! ! ! ! ! ! ! ! ! ! ! !. 43' 43! 43! 44! 44! 45! 46! 46! 47! 48! 48! 48! 49! 49!. PART'III8'EXPERIMENTAL'PART'OF'CLEANING' ' Chapter'58'Laboratory'test' ' ' ' 5.1!Introduction! ! ! ! ! 5.2!Detergent!system!formulation! ! ! 5.2.1!System!XYL! ! ! ! ! 5.2.2!System!XYLJMEK! ! ! ! 5.2.3!System!DDAOJDC! ! ! ! 5.3!Removal!test! ! ! ! ! 5.3.1!Polymer!removal!from!glass!slides! ! 5.3.1.1!Sokrat!2802A!! ! ! 5.3.1.2!Primal!AC33! ! ! ! 5.3.1.3!Paraloid!B72! ! ! ! 5.3.1.4!Observations!! ! ! 5.3.2!Mortar!model!samples! ! ! 5.3.2.1!Sokrat!2802A!! ! !. ' ! ! ! ! ! ! ! ! ! ! ! ! !.

(4) !. Contents!. 5.2.2.2!Primal!AC33! ! ! ! ! ! 53! 5.2.2.3!Paraloid!B72! ! ! ! ! ! 55! 5.4!Final!remarks! ! ! ! ! ! ! 55! ! Chapter'6'–'Physiochemical'properties'determination' ' 57! 6.1!Introduction! ! ! ! ! ! ! 57! 6.2!Spectrophotometer!(colorimetry)!! ! ! ! 57! 6.3!Capillary!rise!test! ! ! ! ! ! ! 59! 6.3.1!Sokrat!2802A! ! ! ! ! ! 60! 6.3.2!Diethyl!carbonate! ! ! ! ! !!!!!!!!!!!!!!!61! 6.4!Vapor!permeability!test! ! ! ! ! ! 64! 6.4.1!Sokrat!2802A! ! ! ! ! ! 64! 6.4.2!Diethyl!carbonate! ! ! ! ! ! 66! 6.5!Scanning!Electron!Microscope!(SEM)! ! ! ! 68! 6.5.1!Sokrat!2802A! ! ! ! ! ! 69! 6.5.2!Diethyl!carbonate! ! ! ! ! ! 70! 6.6!MicroJreflectance!spectroscopy! ! ! ! ! 71! 6.6.1!Sokrat!2802A! ! ! ! ! ! 71! 6.6.2!Diethyl!carbonate! ! ! ! ! ! 73! 6.7!Final!remarks! ! ! ! ! ! ! 75! ' Chapter'78'Archaeological'site'of'Uaxactún' ' ' 77' 7.1!Introduction!! ! ! ! ! ! ! 77! 7.2!Conservation!issues! ! ! ! ! ! 78! 7.3!In!situ!test! ! ! ! ! ! ! ! 79! 7.4!Final!remarks! ! ! ! ! ! ! 80! ! Chapter'88'Archaeological'site'of'Tulum' ' ' ' 83' 8.1!Introduction! ! ! ! ! ! ! 83! 8.2!Conservation!issues! ! ! ! ! ! 84! 8.3!PreJtreatment!examination!! ! ! ! ! 86! 8.3.1!Scanning!Electronic!Microscopy!with!XJray!! microanalysis!(SEM/EDS)! ! ! ! ! !!!!87' 8.3.2!Fourier!TransformJInfrared!Spectroscopy!(FTJIR)!! !!!!89! 8.3.2.1!Magnesium!carbonate! ! ! ! ! !!!!89! 8.3.2.2!Degradations!products! ! !!!!!90! 8.4!In!situ!test! ! ! ! ! ! ! !!!!!!!!!!!!!97! 8.5!Final!remarks! ! ! ! ! !!!!!!!!!!!!!!!!!!!!!!!!!!100!.

(5) Contents! ! Chapter'98'Archaeological'site'of'Templo'Mayor' ' 9.1!Introduction!! ! ! ! ! ! 9.2!Conservation!issues! ! ! ! ! 9.2.1!Restoration!treatments!used!in!the!past! ! 9.3!PreJtreatment!examination! ! ! ! 9.4!In!situ!test! ! ! ! ! ! ! 9.5!Final!remarks! ! ! ! ! ! ! Chapter'108'Systems'characterization'' ' ' 10.1!Introduction! ! ! ! ! ! 10.2!XYL!system! ! ! ! ! ! 10.2.1!Interaction!mechanisms!with!the!polymer! 10.3!DDAOJDC!system!! ! ! ! ! 10.3.1!Structural!characterization! ! ! 10.3.2!DDAO!micelles! ! ! ! ! 10.3.3!DDAOJDC!microemulsion! ! ! ! 10.4!Final!Remarks! ! ! ! ! ! '. '''''''101' !!!!!!!101! !!!!!!!102! !!!!!!!103! !!!!!!!103! !!!!!!!106! !!!!!!!108! '''''''111! !!!!!!!111! !!!!!!!112! !!!!!!!113! !!!!!!!115! !!!!!!!116! !!!!!!!117! !!!!!!!119! !!!!!!!121!. PART'IV'–'FUNDAMENTALS'OF'CONSOLIDATION' ! Chapter'11'8'Consolidation'of'decorative'surfaces'' '''''''123' 11.1!Introduction! ! ! ! ! ! !!!!!!!123! 11.2!Consolidation!of!decorative!surfaces!! ! ! !!!!!!!124! 11.2.1!Barium!or!Ferrioni!Method! ! ! !!!!!!!124! 11.3!Nanomaterials! ! ! ! ! ! !!!!!!!126! 11.3.1!Calcium!hydroxide!!nanoparticles! ! ! !!!!!!!127!! 11.3.2!Barium!hydroxide!nanoparticles! ! ! !!!!!!!129! ! Chapter'128'Nanoparticles'synthesis' ' ' '''''''131' 12.1!Introduction! ! ! ! ! ! !!!!!!!131! 12.2!Nanoparticles!synthesis! ! ! ! ! !!!!!!!132! 12.2.1(Bottom,up!method!! ! ! !!!!!!!!!!!!!!!!!!!!!!133! 12.2.2(Top,down!method!!! ! ! ! !!!!!!!134! 12.2.3!Barium!hydroxide!nanoparticles! ! ! !!!!!!!135! ' ' '.

(6) Contents!. ! PART'V8'EXPERIMENTAL'PART'OF'CONSOLIDATION' ' Chapter'138'Laboratory'test'' ' ' ' ' 13.1!Introduction! ! ! ! ! ! ! 13.2!Consolidation! ! ! ! ! ! ! 13.3!Spectrophotometer!(colorimetry)! ! ! ! 13.4!Optical!microscope! ! ! ! ! ! 13.5!Cotton!swabs!test!! ! ! ! ! ! 13.6!Scanning!Electron!Microscope!(SEM)! ! ! ! 13.7!Capillary!rise!test!! ! ! ! ! ! 13.8!Final!Remarks! ! ! ! ! ! ! ' Chapter'148'Archaeological'site'of'Ixcaquixtla' ' ' 14.1!Introduction! ! ! ! ! ! ! 14.2!Conservation!issues! ! ! ! ! ! 14.3!PreJtreatment!examination! ! ! ! ! 14.3.1!Fourier!TransformJInfrared!Spectroscopy!(FTJIR)! 14.3.2!Scanning!Electronic!Microscopy!with!XJray!! microanalysis!(SEM/EDS)! ! ! ! ! 14.4!In!Situ!Test! ! ! ! ! ! ! 14.5!Final!Remarks! ! ! ! ! ! ! !. 137! 137! 138! 138! 139! 140! 140! 142! 144! 145' 145! 146! 147! 148! !!!!!149! 151! 154!. VI'Final'Conclusions'. '. '. '. '. '. 155'. References!! ! Acknowledgements! Publications! ! ! !. ! ! !. ! ! !. ! ! !. ! ! !. ! ! !. 157! 167! 169!. ! ! !.

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(9) General!Background!and!Aims!. !. formulation! and! characterization! and! apply! the! knowledge! obtained! here! to! the! particular! conservation! issues! present! in! some! of! the! archaeological!sites!of!Mexico.! A! complete! research! endeavor! was! undertaken.! Many! representative!samples!taken!from!14!different!archaeological!sites!were! studied.! The! main! aims! of! the! laboratory! analyses! were! to! identify! synthetic! polymers! on! the! surface! of! the! mural! paintings,! and! ! to! try! to! better! understand! the! mechanisms! of! alteration! and! decay,! including! both! physical! and! chemical! as! well! as! aesthetic! alterations.! The! final! target!was!to!try!to!revert!these!effects,!and!to!find!solutions!for!a!better! appreciation!of!the!mural!paintings.!In!the!following!discussions,!not!all! the!results!obtained!are!reported!due!to!the!large!volume!of!studies!and! analysis! conducted.! Rather,! an! attempt! is! made! to! present! a! representative!but!comprehensive!summary.! ! This! work! has! been! focused! on! the! development! and! characterization! of! nanomaterials! for! restoration! and! conservation! treatments! of! mural! paintings! in# situ! in! different! preSHispanic! archaeological! sites! based! in! two! principle! lines,! cleaning! and! consolidation.! Nowadays! these! are! the! most! debated! and! challenging! issues!of!conservation!science.!The!first!venture!involved!the!cleaning!of! wall! paintings,! particularly! the! removal! of! synthetic! polymers! used! as! consolidants! in! restorations! applied! during! the! past! few! decades! that! have! now! have! become! a! new! source! of! deterioration.! Secondly,! the! consolidation! of! the! pictorial! layers! through! the! use! of! nanoparticles! of! calcium! and! barium! hydroxide,! materials! highly! compatible! with! the! original!substrate!was!investigated.!! The! two! issues! were! addressed! by! performing! experimental! work! on! samples! taken! from! the! sites! and! of! model! samples! in! laboratory,! in! order! to! characterize! in! a! complete! way! the! different! materials! and! evaluate! the! applicability! of! intervention! techniques.! Based!on!the!experimental!results,!different!tests!were!conducted!in!situ! to!verify!the!effectiveness!of!the!products/treatments.!In!particular,!case! studies! of! archaeological! sites! in! Mexico! with! ongoing! restoration! projects!were!undertaken.! ! To! understand! the! aims! of! this! work! the! thesis! was! divided! in! five!parts.!!It!was!essential!first!to!!introduce!some!useful!concepts,!so!in! the!first!chapter!the!kinds!of!material!to!be!conserved,!in!particular!the! mural! paintings,! and! the! conservations! issues! involved! as! well! as! how!. 2! !.

(10) General!Background!and!Aims!. !. and!with!which!techniques!these!issues!have!been!resolved!in!Mexico!to! date!are!presented.!The!advantages!and!disadvantages!of!these!solutions! will! be! discussed! to! understand! why! the! use! of! new! materials! is! proposed.! In! the! second! chapter,! the! theoretical! principles! and! the! conservation! criteria! on! which! the! selection! of! materials! and! interventions!techniques!are!based!are!reported.!! In!the!second!part,!the!synthetic!resins!most!used!in!Mexico!are! explained,! in! that! way! is! possible! to! known! their! behavior! and! general! features.!Then,!the!general!characteristics!of!cleaning!synthetic!polymers! are! exposed.! The! strengths! and! weaknesses! of! these! products! will! be! discussed!in!order!to!elucidate!the!need!for!removal!from!wall!paintings,! currently! an! important! task! for! conservation! scientists.! The! fundamentals! of! cleaning! systems! that! help! in! the! removal! polymer! process!are!discussed.! The! Part! III! is! the! main! part! of! the! work,! is! devoted! to! the! formulation!and!physiochemical!characterization!of!innovative!detergent! systems! with! the! aim! to! resolve! specific! issues! in! three! archaeological! sites.!The!first!part!of!the!work!was!developed!in!laboratory!and!then!the! results!were!tested!in!the!different!archaeological!sites.! In! Part! IV! calcium! and! barium! hydroxide! nanoparticles! are! introduced.! The! argument! for! the! use! of! calcium! and! barium! hydroxide! nanoparticles! for! cleaning! is! made.! Further,! the! different! formulations! utilized! are! presented,! and! the! methods! of! preparation! discussed.! And! finally! in! the! Part! V! the! results! of! tests! carried! out! in! the! laboratory! to! investigate!the!interaction!between!the!calcium!hydroxide!nanoparticles! with!some!original!samples,!and!then!of!several!tests!conducted!on!one! archaeological!site!are!discussed.! In! both! sections,! the! general! conservation! issues! presented! in! wall! paintings! and! some! alternatives! for! their! conservation! and! restoration! were! proposed! based! on! the! stabilization! and! use! of! compatible!materials!with!the!original!materials.! ! ! !. !. 3!.

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(15) Part!I!–!Conservation!in!Mexico!. ! ! the! decorative! elements! realized! on! limeQbased! supports.! However,! depending! of! the! region! and! the! available! materials! it! is! also! possible! find!earthQbased!supports.!! The! artists! did! not! usually! paint! directly! on! the! materials! that! constitute! the! structure! of! the! masonry,! i.e.! stone! blocks.! Rather,! they! painted!on!mortar!layers!that!were!laid!to!create!a!more!uniform!surface.! In!general!terms!a!typical!wall!painting!consists!of!roughly!three!layers! whose! main! structural! component! is! calcium! carbonate,! formed! by! the! reaction!of!lime!(calcium!hydroxide)!with!atmospheric!CO2.!Aggregates! and!water!in!different!proportions!according!to!the!properties!required! are! added! to! slaked! lime! as! a! filler,! to! prevent! shrinkage! and! cracking! upon!drying!and!to!increase!the!mechanical!strength!of!the!plaster.!! ! The!inner!layer,!which!is!laid!on!the!wall,!is!called!arriccio!and!is! the! richest! in! sand.! Moving! towards! the! surface,! the! intonaco! layer! is! found,!consisting!of!a!plaster!that!often!contains!an!equal!amount!of!lime! and!sand.!The!third!and!outer!layer!is!the!paint!layer,!which!is!a!thin!film! (50–! 500! µm! thick)! that! includes! pigments.! It! can! also! be! stratified,! because! the! artist! could! have! laid! more! color! layers! in! order! to! obtain! the! right! visual! effect.! The! two! main! techniques! used! to! realize! a! wall! painting!are!“a(fresco”!and!“a(secco”.!!! ! 1.2.1!The!“a!fresco”!Technique! ! This! term! comes! from! the! italian! word!a( fresco!which! derives! from! the! adjective!fresco!("fresh").! It! describes! a! method! in! which! the! paint! is! applied!on!plaster!on!walls.!In!this(technique!the!pigments!(dispersed!in! lime! water)! are! directly! applied! onto! the! wet! intonaco! layer,! when! the! plaster! begins! to! dry! a! saturated! aqueous! calcium! hydroxide! solution! tends! to! migrate! towards! the! surface! of! the! wall.! Here,! the! Ca(OH)2! reacts!with!atmospheric!CO2! in!order!to!give!calcium!carbonate.!During! this! process! the! pigments! particles! are! “trapped”! into! the! crystalline! carbonate!network!forming!a!smooth!surface![2].!CaCO3!crystals,!indeed,! act! as! an! inorganic! binder! for! the! pigments! and! fix! the! painting! on! the! wall!surface.!The!carbonation!process!starts!from!the!surface!of!the!wall! and!moves!towards!the!interior!of!the!plaster!layer.! ! !. 6! !.

(16) !. !. Chapter!1!–!Conservation!issues!in!Mexico!. ! ! 1.2.2!The!“a!secco”!Technique! ! The! term! a! secco!means! "dry"! in! Italian! and! this! technique! refers! to! a! plaster! that! is! already! dry! when! the! paint! layer! is! applied.! For! this! technique! is! necessary! use! a! medium! to! fix! the! pigments! grains! on! the! plaster!once!applied.!In!this!case!thus!pigments!have!to!be!mixed!with!a! binder!before!their!use.! ! These! terms! should! not! be! confused! with! the! term! fresco-secco( painting,! or! mezzo-fresco( (Italian! for! “halfQfresco”)! technique.! This! technique! consists! of! a! supersaturated! aqueous! solution! of! calcium! hydroxide! with! very! small! particles! in! suspension,! which! gives! the! “milky”!opacity!to!the!system.!It!can!be!used!as!a!medium!for!pigments.! In! this! case! the! binding! properties! are! the! same! as! for! the! fresco( technique,! but! the! rendering! layers! are! already! set,! when! the! paint! is! applied.! In! the! secco! technique,! the! pigments! have! to! be! mixed! with! a! binder! before! their! use.! ! In! the! traditional! European! techniques! two! kinds!of!a(secco(binders!were!used!“tempera”!and!“oil”.!Under!the!generic! term! tempera( painting! are! grouped! several! techniques! in! which! the! pigments!are!mixed!with!a!medium!(i.e.!egg,!casein,!animal!glue,!vegetal! gums),!which!fixes!them!as!it!dries.!Linseed!oil!and!poppyQseed!oil!have! been!used!for!mural!paintings!as!well!as!for!easel!paintings![2].! In! PreQHispanic! mural! paintings! organic! binders! were! widely! used,! mostly! from! barks! of! trees! (gums),! some! plants! like! orchids! and! some! cactaceas.! Historical! descriptions! of! Maya! techniques! dating! from! the!sixteenth!century!describe!painting!binders!based!on!local!tree!gums! such! as! ha'bin! (Piscidia! piscipula),! chakte'! (Caesalpina! mollis),! chucum! (Havardia! albicans),! abal( ak'! (Spondias! spp.),! and! tree! resins! such! as! chaká! (Bursera! sinaruba)! and! huche'! (Codrela! spp.)! [3],! although! these! have!not!yet!been!fully!identified!through!analytical!techniques.!Several! monosaccharide’s! have! been! identified! in! the! paint! layer! by! gas! chromatography! and! mass! spectroscopy! [4]! in! different! archaeological! sites!throughout!the!country.! The!mineral!pigments!of!each!region!were!widely!used!as!colors.! Nevertheless! many! different! plants! colorants! and! colors! like! Maya! blue! (a!complex!mixture!of!palygorskite!clay!and!indigo)!have!been!identified! [4Q5],! adding! to! the! complexity! of! these! paints.! PreQHispanic! mural!. !. 7!.

(17) Part!I!–!Conservation!in!Mexico!. ! ! paintings! in! many! cases! present! mixed! techniques! i.e.! with! the! background!made!by!fresco!techniques!and!all!the!designs!in!tempera.!! ! 1.3!GENERAL!CONSERVATION!ISSUES! ! The! deterioration! of! limeQbased! porous! materials! used! in! artistic/architectural!field!(limeQbased!wall!paintings,!calcareous!stones)! is! one! of! the! most! serious! problems! facing! conservation! today.! The! constant! exposure! to! the! combined! action! of! natural! weathering! and! urban! pollution! causes! severe! damage! to! carbonQbased! materials.! Air! pollution,! soluble! salts! and! bioQdeterioration! are! the! main! causes! of! decay.! Literature! includes! many! papers! concerning! the! investigation! of! their!mechanisms!of!action![6–10].! In! Mexico! archaeological! sites! are! distributed! throughout! the! whole! country.! Since! the! weather! conditions! are! very! different! in! each! area,! different! problems! exist.! In! general! terms,! humidity! is! a! major! cause! of! alteration! in! decorative! elements.! For! example,! depending! on! the! time! of! year! relative! humidity! can! be! up! to! 80%! Q! 100%! in! some! parts! of! southeastern! Republic.! It! is! a! cause! of! physical,! chemical! and! biological!alterations!in!the!constituent!materials,!mainly!those!of!porous! nature.!! !Temperature! is! another! important! factor! to! be! considered! that! alters! the! behavior! of! constituent! materials,! especially! in! cases! where! changes!are!extreme,!with!variations!of!up!to!40!°C.!One!example!is!the! northern! part! of! the! country! where! during! the! day! dry! and! high! temperatures!are!present,!but!in!the!night!a!decrease!of!at!least!30°C!can! occur.! These! variations! cause! expansion! and! contraction! of! materials.! The! deterioration! caused! by! changes! in! the! temperature! in! the! archaeological!materials!is!not!so!much!as!a!result!of!the!absolute!values,! but! rather! of! the! frequency! and! constant! variations.! The! materials! tend! to! expand! and! contract! and! this! action! causes! fractures! or! material! fatigue.! Breaks! occur! from! the! surface! and! as! deterioration! progresses,! the!outer!layers!are!lost.!! One! of! the! main! causes! of! deterioration! is! the! change! in! the! internal! moisture! content! in! the! different! strata! of! mural! painting! or! other! decorative! elements.! Moisture! dissolves! soluble! compounds! and! transports!them!at!the!same!time!towards!a!front!of!evaporation,!which!. 8! !.

(18) !. !. Chapter!1!–!Conservation!issues!in!Mexico!. ! is! usually! a! pictorial! surface.! This! process! is! generally! accompanied! by! volume! expansion.! The! formation! of! new! crystals! inside! the! pores! and/or!at!the!interface!between!the!paint!layer!and!the!plaster!generates! mechanical! stresses! and! results! in! either! lifting! and! detachment! of! the! paint! layer,! or! cracks! and! fissuring! of! the! plaster! [11].! Sulfates! are! commonly! found! as! contaminants! of! wall! paintings,! since! they! result! from! the! chemical! degradation! of! calcium! carbonate! due! to! acid! pollutants! or! by! the! contamination! of! other! materials! like! Portland! cement! used! in! architectonical! consolidations.! Thus,! besides! representing! a! symptom! of! an! ongoing! chemical! degradation! process,! sulfates! favor! further! deterioration! because! of! the! aforementioned! mechanical!stresses![12]! The!physiochemical!action!of!crystallizing!salts!may!result!in!loss! of! adhesion! of! paint! layers! with! a! fine! plaster.! The! pictorial! layer! may! begin! to! fall! off! in! the! form! of! small! flakes.! Also! the! mechanisms! of! dissolution!and!crystallization!of!salts!alter!the!properties!of!the!binders! used! in! paintings! in! tempera! (proteins! or! sugars)! causing! dustiness! or! scaling.! In! addition,,! high! humidity! favors! the! presence! of! microorganisms,!which!cause!changes!in!pH,!which!can!also!degrade!the! binder.!All!of!these!factors,!sometimes,!in!combination!with!poor!quality! of! materials! and! manufacture! techniques! have! resulted! in! the! need! for! the! use! of! consolidating! materials! to! provide! stability! to! the! pictorial! layers!and!ensure!its!permanence!over!the!years.! ! 1.4!PREVIOUS!RESTORATIONS!! ! Wall!paintings!are!an!integral!part!of!monuments!and!sites!and!should!be! preserved! in! situ.! Many! of! the! problems! affecting! wall! paintings! are! linked! to! the! poor! condition! of! the! building! or! structure,! its! improper! use,!lack!of!maintenance,!frequent!repairs!and!alterations.!Also!frequent! restorations,!unnecessary!uncovering,!and!use!of!inappropriate!methods! and! materials! can! result! in! irreparable! damage.! Substandard! and! inadequate! practices! and! professional! qualifications! have! led! to! unfortunate!results![1].! In! past! decades,! new! industrial! synthetic! polymers! successfully! used! in! conservation! and! restorations! treatments! in! Europe,! were! introduced! in! Mexico.! From! the! fifties! to! the! eighties,! chemicals! produced!by!industry!promised!durability,!reversibility!and!permanence!. !. 9!.

(19) Part!I!–!Conservation!in!Mexico!. ! ! of! their! optical! properties.! ! This! conclusion! was! determined! from! tests! performed! in! laboratories! over! very! short! time! periods! without! consideration! for! all! the! variables! presents! in! aged! historic! building! materials!located!in!situ!and!the!constantly!changing!context![13].!These! materials,!have!been!widely!used!for!the!consolidation!of!pictorial!layers! and!the!formulation!of!protective!coatings!in!many!archaeological!sites.! Due! to! the! very! good! adhesion! properties! possessed,! they! film! readily! and!are!easily!applied.!! However,!there!were!no!prior!studies!or!in!situ!investigations!to! fully! understand! how! changes! in! the! physicochemical! properties! of! the! original! substrates,! which! were! made! from! lime! and! their! degradation! could! lead! to! incompatibility! with! the! synthetic! polymers! over! time.! Aged! synthetic! polymer! films,! sometimes! combined! with! calcium! carbonate! concretions,! have! resulted! in! thick! impermeable! layers! that! produce! a! drastic! alteration! of! the! painted! surfaces,! and! also! a! strong! decrease! of! the! water! vapor! permeability! stopping! water! circulation.! Moreover,!one!of!the!main!consequences!of!polymer!degradation!is!a!loss! of!solubility!that!often!makes!their!removal!very!difficult.!! These! effects! have! progressively! led! conservators! to! limit! treatment!materials!to!limeQbased!products!in!such!a!way!that!they!aim! to! behave! as! sacrificial! materials.! For! example! the! effects! of! salt! crystallization! are! usually! strongly! amplified! if! any! protective! coating! was! applied! in! previous! restoration! treatments! on! the! paint! surfaces.! Polymers,! mainly! acrylic! and! vinyl! resins! have! been! widely! used! to! consolidate!wall!paintings!and!to!confer!protection!and!hydroQrepellency! to! the! painted! layer! [14].! Formulations! based! on! acrylate/methacrylate! and! acrylate/vinylacetate! copolymers! have! been! extensively! used! for! decades.! Unfortunately! they! threaten! the! survival! of! works! of! art! and! they! can! now! be! considered! as! one! of! the! most! dangerous! sources! of! degradation.! In! the! presence! of! polymer! films,! salt! crystallization! processes!involve!deeper!areas,!with!stronger!deQcohesion!leading!to!the! complete! powdering! of! the! painting.! The! polymer! closes! the! surface! pores,!generating!mechanical!stresses!towards!the!paint!layer.!! These! polymers! had! been! considered! perfectly! reversible! materials! for! a! long! time.! Unfortunately,! their! reversibility,! that! is,! the! possibility!to!dissolve!them!by!the!same!solvent!used!for!the!application,! has!proven!to!be!a!chimera.!In!fact,!polymer!resins!degrade!quickly!with!. 10! !.

(20) !. !. Chapter!1!–!Conservation!issues!in!Mexico!. ! drastic! variation! of! their! physicochemical! properties! (see! chapter! 3).! Thus,! contrary! to! the! expectations,! polymers! used! for! the! protection! of! wall!paintings!have!induced!further!degradation!of!the!works!of!art!and! subsequent! chemical! modifications,! such! as! crossQlinking,! strongly! hamper!their!removal![15,!12].! On! the! other! hand,! inorganic! materials! have! also! been! used! as! consolidants! in! mural! paintings! and! stone! decorative! elements.! Organosilicone! compounds! based! on! tetraethoxysilane! were! employed! on!sandstone!and!limestone![16].!These!classes!of!compounds!present!a! important!disadvantage!to!their!use!in!conservation!treatments!on!limeQ based! materials:! they! do! not! obey! to! the! fundamental! rule! of! physicochemical! compatibility! with! the! substrate! and! consequently! cannot!be!considered!as!suitable!for!consolidating!purposes![17].! These!classes!of!compounds!present!a!basic!disadvantage!to!their! use! in! conservation! treatments! on! limeQbased! materials:! they! do! not! obey! the! fundamental! rule! of! physicochemical! compatibility! with! the! substrate! and! consequently! cannot! be! considered! as! suitable! for! consolidating! purposes.! Furthermore,! in! the! case! of! ethyl! silicate,! the! mechanism!of!interaction!between!the!consolidant!and!the!matrix!plays! a! crucial! role! in! terms! of! efficacy! of! the! treatment:! when! applied! to! sandstone,!it!can!be!assumed!that!the!alkoxysilane!is!chemically!bond!to! siliceous! minerals! containing! hydroxyl! groups.! But! in! limestone,! such! a! chemical! bond! is! on! a! very! low! scale,! because! limestone! contains! significantly! lower! amounts! of! these! minerals.! Some! researchers! have! even! suggested! that! alkoxysilane! polymerization! may! be! partially! inhibited!in!limestone![18]!Another!factor!to!consider!in!consolidation!of! decaying! limestone! is! that! its! lowQporosity! raises! the! danger! of! formation!of!superficial!crusts.!! For!the!above!reasons,!the!use!of!inorganic!materials!(possibly!of! the!same!materials!used!for!the!works!of!art),!which!are!compatible!with! wall! paintings,! minimizes! the! aforementioned! risks! and! prevents! unexpected! side! effects.! Inorganic! consolidants! are! highly! chemically! stable! and! preserve! the! wall! painting! porosity,! so! ensuring! longQlasting! consolidation!effects.! Nevertheless,! the! low! solubility! of! calcium! hydroxide! in! water! (about!1!g!LQ1)!has!hindered!its!use!for!years.!Saturated!solutions!(limeQ water)! have! been! used! only! in! a! few! specific! cases.! Additionally,! application! of! lime! dispersions! is! hampered! by! the! possible! veil!. !. 11!.

(21) Part!I!–!Conservation!in!Mexico!. ! ! formation! (due! to! the! calcium! hydroxide! reaction! with! carbon! dioxide)! on! the! treated! surfaces! [12].! Whitening! could! be! overcome! by! using! alcoholic! dispersions! of! very! tiny! particles,! with! size! lower! than! that! of! surface!pores,!which!are!in!the!range!of!micrometers!as!will!be!discussed! in!the!following!chapters!! ! 1.5!THE!USE!OF!NANOMATERIALS!IN!MEXICO!! !!!! At!least!for!the!past!17!years,!limeQbased!products!have!been!used!in!an! attempt! to! preserve! the! most! representative! archaeological! mural! paintings! in! Mexico.! Although! changes! in! approaches! and! treatments! were!not!linear,!there!has!been!a!conscious!effort!to!undertake!research! in! order! to! better! understand! traditional! uses! of! lime.! Recently,! some! innovative! techniques! were! developed! at! the! University! of! Florence! (CSGI! Consortium),! designing! formulations! for! either! cleaning! or! consolidation!of!works!of!art.!! Current!research!activity!in!conservation!science!is!largely!based! on! the! paradigm! that! compatibility! of! materials! is! the! most! important! prerequisite! for! obtaining! excellent! and! durable! results.! This! thought! leads!to!the!idea!that!the!original!binder!for!wall!paintings!and!limestone! is!also!their!most!effective!consolidant.!! The!method!was!initially!based!on!the!dispersion!of!slaked!lime! in! shortQ! chain! aliphatic! alcohols! (micronQsized! calcium! hydroxide! particles)![19].!The!procedure!was!afterwards!improved!by!reducing!the! average!size!of!the!consolidating!particles!to!the!subQmicroQ!metric!scale! in! order! to! achieve! a! deeper! penetration! of! the! dispersion,! better! stability!and!avoid!the!formation!of!white!glazing!on!the!treated!surface! [20]!.!! ! In!Mexico!the!introduction!of!this!technology!was!in!2004.!Some! positive!results!in!the!conservation!of!preQHispanic!mural!paintings!were! reported,! as! in! the! case! of! the! archaeological! site! of! Calakmul! in! Campeche! [12,21Q23]! The! use! of! calcium! hydroxide! nanoparticles! has! continued!to!date!in!other!cases!which!have!proved!much!more!complex.! Currently,! for! the! removal! of! aged! polymer! used! in! past! restorations,! the! most! advanced! methods! are! the! use! of! waterQbased! micelles! and! microemulsions! (neat! or! combined! with! gels).! Many! test! were!made!in!different!archaeological!sites!in!Mexico:!“Bebedores”!in!the!. 12! !.

(22) !. !. Chapter!1!–!Conservation!issues!in!Mexico!. ! archaeological!site!of!Cholula![24],!Puebla,!and!the!extend!treatments!in! the! archaeological! site! of! Mayapán,! Yucatán! [25Q26].! Excellent! results! have!been!achieved!with!the!removal!of!Mowilith!coating!applied!on!the! solar!disk!painting![27].!! A! combination! of! different! nanotechnologies! allows! today’s! conservators! to! provide,! in! each! restoration! step,! interventions! respectful!of!the!physiochemical!characteristics!of!the!materials!used!by! artists.! The! “palette”! of! methods! provided! by! nanoscience! is! continuously! enriching! the! field,! and! the! development! of! novel! nanomaterials! and! the! study! of! nanoscale! physiochemical! phenomena! will! further! improve! the! performance! of! restoration! formulations! and! our! understanding! of! degradation! mechanisms.! The! characteristics,! formulations! and! case! studies! of! the! use! of! this! technology,! will! be! exposed!throughout!this!thesis.! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !. !. 13!.

(23) !.

(24) 15.

(25) ,Part,IM,Conservation,in,Mexico, Understanding, authenticity, plays, a, fundamental, role, in, all, scientific, studies,of,cultural,heritage;,in,conservation,and,restoration,planning,,as, well, as, within, the, inscription, procedures, used, for, the, World, Heritage, Convention,and,other,cultural,heritage,inventories,[32].,, Depending, on, the, nature, of, the, cultural, heritage,, its, cultural, context,, and, its, evolution, through, time,, authenticity, judgments, may, be, linked,to,the,worth,of,a,great,variety,of,sources,of,information.,Aspects, of,the,sources,may,include,form,and,design,,materials,and,substance,,use, and, function,, traditions, and, techniques,, location, and, setting,, and, spirit, and, feeling,, and, other, internal, and, external, factors., The, use, of, these, sources, allows, elaboration, of, the, specific, artistic,, historic,, social,, and, scientific,dimensions,of,the,cultural,heritage,being,examined,[32M37].,, Respect,for,the,historical,status,of,archaeological,goods,requires, the, preservation, of, witness, and, material, evidence, that, testify, to, the, history, of, the, life, of, the, artifacts., For, this, reason,, limits, of, intervention, should,be,according,to,material,evidence,in,the,current,state., This, principle, of, authenticity, may, be, kept, if, it, is, allowed, that, most, of, the, existing, historical, material, is, preserved, to, the, extent, possible:, the, legitimacy, of, materials,, its, design,, its, archaeological, potential, and, its, surroundings., All, treatments, of, conservation, and, restoration,carried,out,on,goods,are,acceptable,within,certain,limits,,to, be,vital,for,their,survival,[35], , Interventions, such, as, consolidation, and, cleaning, must, comply, with, minimum, margins, (minimum, intervention), in, order, to, avoid, any, prejudice, in, the, authenticity, of, the, material, and, pictorial, elements., Whenever, possible,, articles, must, be, preserved, in, situ, [1], and, it, is, recommended,that,only,the,necessary,processes,should,be,conducted,to, promote,the,stability,and,integrity,of,goods., , 2.2.2,Principle,of,stability,, , Conservation, should, lead, to, the, stability, of, the, constituent,materials, of, cultural,property,,which,is,determined,from,the,moment,of,its,creation., This, principle, aims, to, restore, and, maintain, the, minor, alteration, physicochemical,, formal, and, structural, constituent, materials, of, decorative,elements,and,architectural,coatings,[34]., ! !. 16.

(26) Chapter,2,–,Theoretical,guidelines,for,conservation,, 2.2.3,Principle,of,integrity, , Integrity,is,understood,as,values,that,give,meaning,and,relevance,to,the, cultural, heritage., So, operations, that, have, to, be, carried, out, should, be, made, at, the, minimum, level, needed, and, hold, these, values,, respecting, completely, the, physical,, historical, and, aesthetic, aspects,, including, the, evidence, of, its, origin,, its, original, constitution,, the, materials, that, compose, them,, appearance, and, texture,, losses, as, a, testimony, of, the, passage,of,time,and,information,they,contain,,as,they,are,the,intentions, of, the, manufacturer, and, the, technology, used, in, its, manufacture., Therefore,, the, maintenance, of, integrity, of, onMsite, monuments, and, ensembles, should, be, the, fundamental, objective, of, the, conservation, of, the,archaeological,heritage,,unless,stability,could,be,at,risk,[34], , 2.2.4,Principle,of,Legibility, , Conservation,should,promote,legibility,and,the,values,of,archaeological, goods,, which, means, that, its, results, should, lead, to, the, appreciation, of, their, integrity, and, authenticity., This, means, not, only, to, promote, the, understanding, of, heritage, in, the, sense, of, appreciation, of, its, formal, characteristics,, attributes,, detectable, features, and, material, traces, acquired,during,their,life,history,,but,also,understanding,sequences,and, harmonic, information,, symbolism,, plasticity, and, iconographies, of, their, physical,attributes,[34]., , 2.3,CRITERIA,FOR,INTERVENTION,, 2.3.1,Compatibility, , The, first, of, these, criteria, is, the, physioMchemical, compatibility, of, the, materials, used, in, the, intervention., , This, means, that, its, chemical, composition,should,be,similar,or,equal,,and,should,not,modify,,alter,or, chemically,destroy,the,material,values,that,you,want,to,keep.,Therefore,, chemical, compatibility, refers, to, the, fact, that, undesirable, chemical, reactions,between,the,restorative,material,and,cultural,values,should,be, prevented, and, as, much, as, possible, byMproduct, or, contrasts, mechanics, should, not, be, generated., Hence,, the, importance, of, knowing, the, constituent, materials, and, technique, of, manufacture, of, the, object,, in, order, to, choose, the, most, compatible, with, the, original, restoration,. 17.

(27) ,Part,IM,Conservation,in,Mexico, material, and, ensure, maximum, durability, as, well, as, chemical, and, thermodynamic,stability,[37]., , 2.3.2,Reversibility, , Reversibility,was,considered,a,rule,that,had,to,be,strictly,followed,in,any, treatment,or,material,applied,in,restoration.,The,main,idea,was,have,the, possibility, of, removing, any, material, used, in, previous, restorations, that, could,be,a,potential,damaging,agent,and,without,injuring,the,integrity,of, the, object., This, criterion, was, proposed, because, it, has, been, observed, that,some,restoration,products,also,undergo,a,process,of,deterioration,, failing,to,fulfill,its,function,,so,it,is,necessary,to,eliminate,them,to,apply, new, ones., It, is, not, easy, to, meet, this, criterion,, especially, in, processes, where,the,reversibility,of,the,products,is,virtually,impossible,,as,it,is,the, case, with, the, consolidation, process., When, it, is, a, process, that, aims, to, restore, structural, stability,, cohesion, between, particles, and, adhesion, to, the, substrate,, applying, a, consolidating, or, a, fixative,, removing, this, product, implies, its, extraction.,This, is,almost, unlikely, (or, at, least, risky), in, the, inner, layers, of, a, mural, painting,, since, the, reversible, process, removes, the, material, and, returns, the, original, instability, and, increases, the,possibility,of,loss.,Reversibility,does,not,exist!!,Is,almost,impossible, to,reverse,any,conservation,or,restoration,treatment., For, this, reason,, it, is, important, to, know, the, characteristics, of, a, consolidation,on,the,paint,layer,to,which,is,to,be,applied,,as,well,as,the, possible, behavior, of, the, product, under, certain, conditions, to, avoid, having,to,seek,the,reversibility,process,[37],, ! 2.3.3,ReMtreatability,, , Considering,how,complex,it,can,be,to,fulfill,the,criterion,of,reversibility,, the, criterion, of, reMtreatability, is, vital., ReMtreatability, can, be, defined, as, the, possibility, of, applying, restoration, treatments, that, allow, future, interventions,, either, by, proposed, progressive, treatments,, improved, procedures, or, alternative, techniques, without, negative, results, [37]., Not, only, the, shape, of, the, work, of, art, but, also, the, potential, changes, to, its, chemical,composition,and,to,its,microstructure,must,be,considered.,The, concepts,of,physicMchemical,compatibility,and,durability,is,implied,here., ,. 18.

(28) Chapter,2,–,Theoretical,guidelines,for,conservation,, 2.4,DEFINITIONS,OF,TREATMENTS,, , The, principles, and, criteria, guiding, the, implementation, of, restoration, treatments, have, been, discussed., Consolidation, operations, fundamental, to,the,conservation,of,mural,paintings,and,decorative,elements,are,now, discussed., , 2.4.1,Consolidation,and,fixing,mural,paintings, , Consolidation, and, fixing, of, stucco, and, paint, layers, in, mural, paintings, during, the, last, fifty, years, allowed, the, comparison, of, the, behavior, of, products, of, organic, and, inorganic, nature, and, the, choice, of, one, or, the, other,depending,on,the,constituent,materials,,environmental,conditions, and, pictorial, technique, to, which, these, cultural, goods, are, exposed., For, this, reason,, it, is, essential, in, the, first, instance,, to, know, the, degree, of, cohesion,of,the,pictorial,film,and,its,adhesion,to,the,mortar,,as,well,as,to, the,wall,support., In,our,point,of,view,and,according,to,the,established,protocols,in, the, national, coordination, of, conservation, in, Mexico, (CNCPCMINAH),, the, processes,of,consolidation,and,fixing,must,be,clearly,differentiated,,since, they, are, carried, out, for, different, reasons., The, consolidation, process, is, carried,out,in,order,to,return,the,internal,cohesion,between,particles,of, pigment,by,the,loss,of,the,binder,or,support.,Fixing,,on,the,other,hand,, has,the,function,of,joining,or,acceding,detachments,among,the,different, strata,of,the,pictorial,layer., The, pictorial, layer, disintegrates, into, dust, or, becomes, powdery, from, the, loss, of, cohesion, between, particles, of, pigment, and, lack, of, adhesion,to,the,substrate.,This,can,happen,as,a,result,of,faulty,technique, of, manufacture, or, by, the, action, of, a, set, of, physical,, chemical,, and, biological,phenomena,that,change,the,nature,of,the,substance,cementing, or,bonding,agents,,depending,on,the,original,cohesion.,Sometimes,only, the,electrostatic,force,is,what,allows,the,permanence,of,the,pigment,on, the,surface,,with,the,risk,that,at,any,time,it,falls,off,and,is,lost,before,a, mechanical,action,(see,chapter,1)., In,general,,the,processes,of,consolidation,and,fixation,use,natural, or,synthetic,organic,products,that,have,adhesive,properties.,However,,it, should, be, noted, that, for, reasons, previously, discussed,, materials, of, inorganic,origin,are,currently,chosen,for,murals.,. 19.

(29) ,Part,IM,Conservation,in,Mexico, Materials, that, act, as, consolidants, or, fixatives, are, mixed, with, a, dispersing, agent, needed, for, it, application., For, good, results,, it, is, necessary, that, materials, penetrate, to, a, depth, of, at, least, two, or, three, millimeters,to,avoid,superficial,films,or,the,accumulation,of,material,in, the,outer,layers.,This,result,depends,on,whether,emulsions,or,solutions, are,used,,the,polarity,and,surface,tension,of,both,substances,and,on,the, substrate,and,the,volatility,of,the,dispersing,agents,,among,other,points, [2]., Moreover,, the, consolidant, or, fixative,, depending, on, the, case,, should,not,alter,the,structural,properties,of,the,original,,such,as,porosity, materials,, since, this, could, interfere, with, the, flow, of, gases, and, liquids, through,the,surface,of,the,wall., , 2.5,FINAL,REMARKS, , In, conclusion,, any, treatment, in, conservation, should, follow, several, principles,, internationally, established., Any, attempts, to, develop, new, materials, should, be, based, on, those, principles,, as, noted, by, several, authors., • Any, material, in, the, conservation, treatment, must, not, alter, the, integrity,and,authenticity,of,the,object., • Any, material/treatment, must, present, potential, reMtreatability, allowing, further, interventions, of, restoration,, whenever, necessary., • Any, material/treatment, must, be, compatible, with, all, the, materials,encapsulated,by,the,object;,the,"artistic",materials,are, to,be,treated,as,a,whole,and,not,separately., ,. 20.

(30) ! ! ! ! ! ! ! ! ! ! ! !. ! PART!II!. FUNDAMENTALS!OF!CLEANING!.

(31) !.

(32)

(33) "Part"IIM"Fundamentals"of"Cleaning". " " 3.2"ARYLIC"RESINS" " Acrylic"polymers"are"a"group"of"macromolecules,"which"were"extensively" used"in"the"field"of"restoration,"especially"in"the"field"of"paints"and"also"in" fixatives"and"consolidating."They"are"virtually"colorless"and"transparent," have" a" low" tendency" to" yellowing" and" are" very" stable" towards" most" of" the"atmospheric"agents"[40]." Acrylic" polymers" encompass" a" wide" range" of" high" molecular" weight" polymers" that" are" based" on" the" esters" of" acrylic" acid" and" methacrylic" acid." They" produce" a" wide" variety" of" resins" with" many" applications." Depending" on" the" nature" of" the" alcoholic" residue" the" properties" of" the" polymer" significantly" change." The" properties" also" depend"on"the"length"of"the"substituent"increasing"the"size"decreases"the" hardness"of"the"polymer."When"the"resins"become"softer"their"adhesive" properties" are" increased" and" become" more" easily" soluble" in" nonMpolar" solvents."" Methyl" and" ethyl" polyacrylates" are" generally" soluble" in" middleM low" polarity" solvents," and" insoluble" in" aliphatic" hydrocarbons" mixtures" with" some" aromatic" compound." Butyl" acrylates," on" the" other" hand," are" also"soluble"in"these"less"polar"mixtures."Moreover,"they"have"a"lower"Tg& than" ethyl" and" methyl" acrylates" and" thus" they" usually" are" more" plastic" and"flexible."This"is"obviously"valid"only"for"homopolymers."In"the"case"of" copolymers" the" properties" depend" on" the" nature" and" on" the" relative" amounts"of"the"two"monomers."The"monomers"of"these"resins"have"low" viscosity,"however,"have"a"strong"tendency"to"polymerize,"which"allows" using"them"directly"as"a"consolidant"by"impregnating"the"materials"to"the" porous"structure"and"degraded"[40M42]." Generally" speaking," the" weakness" of" acrylic" resins" is" their" sensitivity" to" UV" irradiation." Methacrylates" tend" to" undergo" chain" scissoring,"while"acrylates"are"more"inclined"to"crosslinking"phenomena" [41]."" FTIR" differentiates" the" various" acrylics" varnishes" and" media." Is" important"to"know"the"characteristics"of"the"spectra"for"the"identification" of"the"polymer"presents"in"the"paintings."Some"spectra"of"the"most"used" acrylic"solutions"will"shown." " ". 22" ".

(34) Chapter"3"–"Synthetic"Resins". " 3.2.1"Paraloid"B72©" " Paraloid"B72©"certainly"is"the"most"widely"used"resin"in"conservation"of" cultural" heritage." It" is" used" on" almost" every" material" as" a" binder," an" adhesive," a" protective" or" a" consolidant." It" is" an" acrylic/methacrylic" copolymer"composed"of"ethyl"methacrylate"and"methyl"acrylate"in"a"ratio" of" 70:30." It" has" a" high" average" molecular" weight" of" about" 70.000" uma." And"has"a"Tg"of"40˚C"[40,42]."" ". ". ". Figure"3.1."FTIR"spectrum"of"Paraloid"B72©."The"characteristic"absorptions"are" 2988"and"2955"cmM1"CMH"Stretch;"1730"cmM1"C=O"stretch,"1449"and"1387"cmM1"CMH" stretch;"1263,"1238,"1170,"1150,"1028,"972"cmM1"CMO"&"CMC"stretch;"862"and"756" cmM1"CMH"Rock"[40]."Paraloid"B72"pellets"were"purchased"from"Zecchi,"Florence."". " Paraloid" B72©" comes" in" transparent" grains," also" known" as" drops" or" pellets" and" is" soluble" in" ketones," esters," alcoholMethers," chlorinated" and" aromatics" hydrocarbons" but" insoluble" in" aliphatic" hydrocarbons" and" isopropyl"alcohol"and"only"slightly"soluble"in"ethyl"alcohol." Even"if"the"resulting"solution"may"take"a"milky"color,"the"film"that" is" formed" on" the" treated" surfaces" is" transparent." The" treated" areas" can" take" on" a" shiny" appearance" ("melted")," especially" if" the" resin" is" used" at" relatively" high" concentrations." In" addition," the" color" of" the" specimen" to" be"restored"is"intensified."Within"the"acrylics"available"in"the"market"this" is"one"of"the"best"quality,"at"least"from"evidence"of"aging.". ". 23".

(35) "Part"IIM"Fundamentals"of"Cleaning". " " 3.2.2"Primal"AC33©"" " Primal" is" also" commercially" known" as" Rhoplex" AC33©." It" is" a" low" viscosity" aqueous" emulsion" of" an" acrylic" polymer." This" copolymer" is" composed"of"ethyl"acrylate"and"methyl"methacrylate"in"a"ratio"of"66:34." It"is"a"milky"white"liquid"in"injection"with"the"aim"of"adhering"detached" substrates"with"good"adhesive"properties"[42]."" ". ". " Figure"3.2."FTIR"spectrum"of"Primal"AC33©."The"characteristic"absorptions"are" 2983,""2950"and"2891"cmM1"CMH"Stretch;"1724"cmM1"C=O"stretch,"1449,"1382"and" 1344"cmM1"CMH"stretch;"1236,"1153,"1225,"1020,"964"cmM1"CMO"&"CMC"stretch;"[40]." Primal"AC33"aqueous"emulsion"was"purchased"from"Phase"Restauro,"Florence.". ". 3.3"POLYVINYL"ACETATE"RESINS" " Ethylene"can"also"be"considered"the"precursor"of"a"series"of"derivatives" of" fundamentally" important" polymers:" vinyl" derivatives." The" most" important" for" their" adhesive" properties" is" the" polyvinyl" alcohol" (PVAl)" and"its"derivatives"polyvinylacetate"(PVAc)." PVAc"is"a"macromolecule"of"medium"polarity,"for"example"in"the" solubility"of"the"solid"polyvinyl"acetate,"ranging"from"very"polar"solvents" (alcohol)" down" until" aromatic" hydrocarbons" (toluene)." The" macromolecule"of"polyvinyl"acetate"undergoes"spontaneous"degradation". 24" ".

(36) Chapter"3"–"Synthetic"Resins". " over"time,"as"a"result"of"aging"and"a"combination"of"other"factors,"such"as" temperature,"humidity"and"condensation"[40]." On" the" other" hand," the" polarity" of" PVAl" is" very" high" (because" of" the"free"hydroxyl/–OH"present"in"large"numbers"on"the"macromolecule)," so" the" polymer" is" soluble" in" water," remains" soluble" in" the" more" polar" solvents" like" alcohol," but" is" practically" insoluble" in" other" less" polar" organic"solvents."PVAl"is"a"good"adhesive,"and"is"also"used"as"a"hardener" for"the"paint"layers,"in"particular"temperas,"for"its"opacity"[42]." Mexican" restoration" intervention" reports" documented" the" application"of"Curasol"AR©"(a"PVA"made"by"Hoechst"Chemical"Industry)" and" Endurol©" (a" PVAL" made" by" Poldi," S.A.)." The" use" of" different" PVAL" (polyvinyl" alcohol)" emulsions" and" PVA" (polyvinyl" acetate)" to" adhere" a" fabric" to" the" surface" for" the" facing" procedure" have" also" been" reported" (sometimes"a"mixture"of"Mowilith"DM1H©,"Mowilith"DHLR"or"DM4)"[43M 45]" " Some" FTIR" spectrum" of" the" polymers" Endurol©" and" Curasol©" used"in"restorations"in"Mexico"were"obtained."The"polymers"came"from" warehouses"of"the"CNCPCMINAH,"who"gave"the"materials"to"be"analysed." ". ". " Figure"3.3."FTIR"spectrum"of"Endurol©."The"characteristic"absorptions" observed"are"3380,"3298,"2962,""2932"cmM1"CMH"Stretch;"1730"cmM1"C=O"stretch," 1591,"1429,"1365"cmM1"CMH"stretch;"1226,"1128,"1074,1018"and"9643"cmM1"CMO"&" CMC"stretch". ". ". 25".

(37) "Part"IIM"Fundamentals"of"Cleaning". ". ". " Figure"3.4."FTIR"spectrum"of"Curasol©."The"characteristic"absorptions"observed" are"2958,"and"2871"cmM1"CMH"Stretch;"1728"cmM1"C=O"stretch,"""1434"and"1369" cmM1"CMH"stretch;"1224,"1164,"1020,"943"cmM1"CMO"&"CMC"stretch.". " 3.4"STYRENE"ACRYLATE"RESINS" " Styrene" Acrylic" resins" are" more" resistant" to" saponification" and" absorb" less" water" than" the" pure" acrylic," however," are" more" sensitive" to" UV." Therefore"should"not"be"used"as"a"transparent"film,"but"only"as"binders" for" pigments" and" fillers." One" of" the" critical" points" in" the" use" of" these" materials"is"the"almost"always"unknown"composition"of"the"additives,"as" surfactants," plasticizers," biocides," which" is" often" not" declared" by" the" manufacturer"[42]." " 3.4.1"Sokrat"2802A©" " Sokrat©," also" commercially" known" as" Axilat" 2802©" is" an" anionic" aqueous" dispersion" of" a" styrene/ethylMhexyl" acrylate" copolymer," especially" used" in" the" building" industry" in" the" Czech" Republic," which" became"a"common"consolidant"for"wall"paintings"in"the"1990s"[46]."This" product"is"usually"employed"as"a"binder"for"the"production"of"caulks"and" sealants"used"in"modern"buildings."It"is"also"used"for"the"modification"of" hydraulic" mortars," where" it" helps" to" form" a" good" transparent," smooth," soft,"highly"flexible"and"slightly"sticky"film"[47]."Sokrat"2802A©"can"also". 26" ".

(38) Chapter"3"–"Synthetic"Resins". " be"used"for"the"formulation"of"tile"adhesives"and"selfMleveling"compounds" [48]." Finally," concrete" and" cement" for" the" construction" of" modern" buildings" are" treated" with" this" polymer," in" order" to" increase" the" waterproofing"properties"of"the"final"material."Once"its"dispersing"phase" (i.e." water)" is" evaporated," Sokrat©" forms" thick," elastic" and" resistant" films,"which"can"be"dissolved"slightly"by"a"few"organic"solvents."" ". ". " Figure"3.5."FTIR"spectrum"of"Sokrat©."The"characteristic"absorptions"observed" are"2923,"2860"cmM1"CMH"Stretch;"the"aromatic"CMH"stretching"peaks"from"the" styrene"3027."The"carbonyl"stretching"at"1727"cmM1"C=O;"the"aromatic"ring" breathing"at"1600,"1494"and;"1253,"1153,"1029"cmM1"CMO"&"CMC"stretch"and"CMH" rocking"756"and"698"[40].". " " 3.5"DUPONT"PRODUCTS". " At" least" three" important" archaeological" sites" in" Mexico" was" reported" in" the"50’s"the"use"of"Duco®"and"Dulux®"like"protective"coatings"in"mural" paintings." Duco®" and" Dulux®" are" two" trade" names" assigned" to" automotive"coatings"developed"by"the"DuPont"Company"in"the"1920M30s," and"essentially"composed"of"nitrocelluloseMbased"pyroxylin"lacquers"and" an"alkyd"resin"enamel"respectively." Actually" these" products" are" not" commercially" available," DuPont" sold"its"consumer"paint"business"in"1983."The"Dulux®"brand"is"now"sold". ". 27".

(39) "Part"IIM"Fundamentals"of"Cleaning". " by" ICI," a" British" company" with" a" worldwide" distribution" network," with" the" ICI" acronym" denoting" Imperial" Chemicals" Industries." ICI" Dulux®" is" now" a" 100" percent" acrylic" paint" with" zero" volatile" organic" compounds" (or"VOCs,"which"are"environmentally"harmful"solvents)"[49]." 3.5.1"Nitrocellulose"lacquers" " “Nitrocellulose”" and" “pyroxylin”" are" terms" used" to" describe" a" range" of" paints" and" lacquers" that" contain" blends" of" cellulose" nitrate" polymer."" Cellulose"nitrate"(which"is,"strictly"speaking,"a"modified"natural"polymer)" requires"modification"for"use"as"a"binding"medium,"typically"by"blending" it" with" a" second" resin" (to" improve" gloss," adhesion" and" hardness)" and" adding"significant"amounts"of"plasticizer"(to"confer"elasticity"on"the"film)" [40].""" " Cellulose" nitrate" was" extensively" used" from" 1877" onward" to" manufacture"a"wide"variety"of"articles."This"polymer"is"used"in"the"arts"as" a" component" of" coatings," primers," and" lacquers," together" with" alkyd" resins" and" phthalate" compounds" that" are" added" as" plasticizers." This" formulation" improves" the" adhesion" and" hardness" properties" of" the" medium." Solutions" of" this" polymer" in" organic" solvents" such" as" ethyl" acetate"have"been"frequently"used"in"restoration"tasks"as"adhesives"and" consolidants"[50].". " 3.5.2"Alkyd"resins" " Alkyd" resins" are" oilMmodified" polyesters" and" were" introduced" in" the" early" 1930s." The" incorporation" of" oil" is" required" to" produce" sufficient" flexibility"of"the"polyester"formulation"so"that"a"resin"suitable"for"use"as" film" results" [40]." " The" term" “alkyd”" derives" from" the" polyester" component’s" two" main" components:" a" polyhydric" alcohol" (also" called" polyol)" and" a" polyMbasic" carboxylic" acid" (or" poly" acid)." For" the" production" of" a" usable" alkyd" resin," the" polyacid" must" have" at" least" two" acid"(MCO2H)"groups)."Whereas"the"polyol"must"be"at"least"trihydric;"that" is," it" must" contain" at" least" three" hydroxy" (MOH)" groups." " The" polyester" produced" from" these" two" components" is" typically" a" hard," crossMlinked" thermosetting" resin," but" by" incorporating" a" monobasic" fatty" acid," the" degree"of"crossMlinking"is"significantly"reduced."A"drying"oil"is"often"used". 28" ".

(40) Chapter"3"–"Synthetic"Resins". " as" the" source" of" monobasic" acid," and" results" in" the" “oilMmodified”" alkyd" [40].""" ! 3.6"POLYMER"DEGRADATION" " It" must" be" assumed" that" the" behavior" of" a" polymer" with" the" passage" of" time" cannot" be" predicted" on" the" basis" of" theoretical" considerations." Polymer" degradation" is" influenced" for" weathering" conditions" like" temperature," humidity," illumination" and" atmospheric" pollution." But" attention" must" be" paid" to" the" intrinsic" degradation" of" the" polymer" structure," i.e." not" only" is" the" chemical" formula" important" but" also" the" presence" of" other" additives" (plasticizers," surfactants," biocides," antioxidants"etc.)." The" degradation" structure" of" the" polymers" is" principally" due" to" three" phenomena" that" affect" their" physical" and" optical" properties," therefore"their"functionality"[42]." • DeMpolymerization:" this" is" chain" fragmentation" and" occurs" primarily" by" hydrolysis," that" is," the" breaking" of" bonds" between" constituent"monomers"by"water." • CrossMlinking" when" the" adjacent" chains" are" combined" with" the" formation"of"new"bonds." • New"functional"groups"formation,"usually"with"increased"polarity" and"the"onset"of"yellowing."The"combined"action"of"UV"rays"and" oxygen" results" in" peroxide" chain" groups," which" can" then" evolve" into"alcohol"or"carbonyl"groups." " Degradation" has" different" consequences" on" the" polymers" [51M54]." The" effect" on" optical" characteristics" cannot" be" overlooked," as" in" this" field" of" work," the" readability" of" an" art" work" is" crucial" and" the" yellowish" and" chromatic" changes" on" the" treated" surface" are" not" acceptable." Also," increasing" polymer" polarity" is" always" associated" with" aging" and" is" reflected"in"the"loss"of"solubility"of"the"material." Many" weather" conditions" influence" the" degradation" of" the" polymers."The"increase"in"temperature"always"leads"to"an"increase"in"the" speed" of" degradation." The" action" of" water" (humidity)" is" involved" in" all" hydrolysis" mechanisms." In" general," oxygen" is" the" principal" source" of" degradation."Oxygen"may"be"involved"in"degradation"reactions"either"in" the" presence" of" light" (photoMoxidation)" or" in" the" dark" (autoMoxidation).". ". 29".

(41) "Part"IIM"Fundamentals"of"Cleaning". " Oxygen"binds"to"the"polymer"chains"with"the"formation"of"a"new"reactive" radical"that"evolves"towards"more"stable"forms"with"formation"of"crossM linking" or" various" oxygen" structures." These" macroMradicals" can" interact" with" other" polymeric" chains" through" crosslinking" phenomena" resulting" in"the"lowering"of"the"product"solubility." " Light" (UVMVisible" radiation)" induces" two" kinds" of" reactions:" photoMoxidation:" depending" on" the" intensity" of" the" radiation" hydroperoxides" may" evolve" into" different" types" of" free" radicals." Secondly," without" the" presence" of" oxygen," radiation" can" be" absorbed" in" the" most" sensitive" areas" of" the" molecule," for" example" by" double" bonds," and" in" general" by" the" chromophore" groups," to" give" free" radicals." These" phenomena"can"lead"to"a"yellowing"of"the"polymer"film." Generally" speaking," one" of" the" most" dangerous" ways" of" degradation"for"a"polymer"used"in"conservation"of"cultural"heritage"is"the" formation" of" crosslinking." This" invariably" leads" to" a" decrease" in" the" solubility"of"the"material"and"thus"to"the"irreversibility"of"the"treatment." Polymers" with" glass" transition" temperature" (Tg)" much" higher" than" ambient"temperature"are"less"sensitive"to"crosslinking"because"polymer" chains"are"somewhat"“more"blocked”"and"thus"less"inclined"to"interact." " In" summary," polymers" have" been" considered" to" be" reversible," based" on" the" assumption" that" the" same" solvent" could" be" used" for" their" removal."As"discussed,"one"of"the"most"important"undesired"side"effects" is" the" chemical" and/or" physical" degradation" upon" ageing" of" these" macromolecular" compounds" due" to" the" photochemical" reactivity" and" thermal" degradation." The" combined" action" of" the" light," temperature," oxygen" and" relative" humidity" may" have" undesirable" effects" like" the" change" of" color" (yellowing" or" opaque" layer)," formation" of" microM fractures"and"loss"of"solubility."After"some"years"of"the"application"of"the" polymer," it" has" been" demonstrated" that" these" materials" become" insoluble" [38]." Actually," the" removal" of" polymers" previously" used" in" restoration"is"the"central"challenge"of"modern"conservation"science." Unfortunately"most"of"these"materials"are"still"applied"even"when" the" same" polymeric" coatings" applied" in" past" interventions" have" clearly" shown" different" undesired" effects." Owing" to" these" degradation" phenomena," that" affects" not" only" the" polymer" film," but" the" original" material" there" is" a" strong" alteration" in" the" physioMchemical" properties." Therefore"conservation"procedures"on"previously"treated"paintings"must". 30" ".

(42) Chapter"3"–"Synthetic"Resins". " very" often" deal" with" the" removal" of" aged" coatings." " For" that" reason" is" very"important"make"an"appropriate"choice"of"the"cleaning"agents."This" issue"will"be"discussed"in"the"next"chapters." " ". ". 31".

(43) !.

(44)

(45) "Part"IIU"Fundamentals"of"Cleaning". " layer" of" the" “foreign”" material" leading" to" relevant" reduction" of" the" adhesion" forces" between" the" hydrophobic" polymeric" chains" and" the" substrates." " Swelling" of" polymers" is" one" of" the" most" important" mechanisms" through" the" “foreign”" materials" can" be" removed" from" the" surfaces"of"works"of"art"[38]." This" can" be" achieved" by" using" amphiphileUbased" colloidal" systems"such"as"microemulsions"and/or"micellar"solutions."" " These" detergent" systems" are" able" to" remove" these" aged" materials." Each" component" that" conforms" to" these" systems" and" their" properties"will"be"discussed"here.". " 4.2"SURFACTANTS". " The" term" surfactant" comes" from" “surfaceUactive" agent”" and" describes" their" capability" to" modify" the" surface" energy" between" two" immiscible" phases,"such"as"oil"and"water."They"belong"to"the"amphiphile"class."Their" structure"combines"two"parts."One"is"the"hydrophilic"part"(head)"which" interacts" with" water" or" solvent," and" the" other" is" the" hydrophobic" part" (tail),"which"avoids"any"contact"with"water."For"that"reason"they"have"a" different" interaction" with" a" common" selective" solvent," and" in" water" produce" a" wide" family" of" nanoUsized" aggregates." The" two" incompatible" units"are"linked"together"by"a"covalent"bond;"in"that"way"they"cannot"be" separated" but" are" forced" to" remain" bound" in" the" same" molecular" entity" resulting" in" particular" properties" and" different" behavior" in" aqueous" dispersions."The"hydrophobic"and"the"hydrophilic"parts"of"the"surfactant" establish" different" interactions" (polar" and" apolar)" with" a" “selective”" solvent." This" is" the" mechanism" that" guides" the" behavior" of" amphiphiles" in" a" water" solution," namely" the" formation" of" selfUassembled" aggregates" such"as"micelles"[38,"54]." Numerous" variations" are" possible" within" the" structure" of" both" the" head" and" the" tail" groups" of" surfactants." The" head" group" can" be" charged"or"neutral,"small"and"compact"in"size,"or"a"polymeric"chain."The" tail"group"is"usually"a"single"or"double,"straight"or"branched"hydrocarbon" chain," but" it" may" also" be" a" fluorocarbon" or" a" siloxane," or" can" contain" aromatic"groups"[55].". " ". 34" ".