# Deterioration of White Tempera Mock-Ups Paints in a SO\({}_{2}\)-Rich Atmosphere
## 5 Conclusions  
In this research, white tempera mock-ups composed of a pigment (calcite, Bianco di San Giovanni, gypsum or lead white) mixed with an organic binder (rabbit glue or egg yolk) were exposed to a SO\({}_{2}\)-rich atmosphere in order to evaluate the physical, chemical and mineralogical changes. Firstly, verifying the composition and grain size of pigments was crucial to ensure reliable and accurate results. It was confirmed that these tempera paints were susceptible to sulfation which resulted from SO\({}_{2}\) deposition. This sulfation was revealed through the formation of sulfur-based salts (both sulfates and sulfites) because of the dissolution of the pigments. The amount of salts formed was similar in paints made with egg yolk and rabbit glue, contrary to what was found in tempera paint mock-ups made with other pigments subjected to the same SO\({}_{2}\) aging test. Therefore, it can be concluded that, in the case of tempera paints made with calcite, gypsum and lead carbonate, the nature of the binder (egg yolk or rabbit glue) did not influence the reactivity to sulfation by means of SO\({}_{2}\) gas exposure. Spectrophotometry confirmed that the color of the paints slightly changed after aging, more intensely in egg-yolk-based paints. In these paints, a greater modification of roughness was also detected after the SO\({}_{2}\) test. Given that the amount and type of salts formed was similar in the paints regardless of the binder, the changes in color and roughness in the egg-yolk-based tempera could be due to the deterioration of the egg yolk binder, which would be more sensitive than rabbit glue to the sulfation process by wet deposition of SO\({}_{2}\). However, no chemical changes were detected on the binders. Therefore, it could be highlighted that, contrary to what happens with temperas made with other pigments exposed to the same aging test, temperas made with the selected white pigments show higher resistance to the SO\({}_{2}\) test. Finally, it would be necessary to apply more sensitive analytical techniques capable of detecting minimal changes in the organic binders to explain the slight changes in color and roughness.  
Conceptualization, T.R., J.S.P.-A. and C.C.; methodology, T.R., J.S.P.-A. and C.C.; software, J.S.P.-A.; validation, T.R., J.S.P.-A. and C.C.; formal analysis, T.R., J.S.P.-A., D.J.-D. and C.C.; investigation, T.R., J.S.P.-A., A.D. and C.C.; resources, T.R., J.S.P.-A., A.D. and C.C.; data curation, J.S.P.-A. and D.J.-D.; writing--original draft preparation, T.R., J.S.P.-A. and D.J.-D.; writing--review and editing, A.D. and C.C.; visualization, T.R. and C.C.; supervision, T.R., J.S.P.-A. and C.C.; project administration, T.R., J.S.P.-A. and C.C.; funding acquisition, T.R., J.S.P.-A. and C.C. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Spanish Research Projects AERIMPACT (CGL2012-30729), EXPOAIR (P12-FQM-1889), LASERING-PH (PID2021-1233950A-100), the European Regional Development Fund (ERDF) and the Andalusian Research Group RNM-179.  
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
Analyses were performed in the CACTI (_Centro de Apoyo a la Investigacion_) Research Support Centre at the University of Vigo. [PERSON] was supported by the RYC2020-028902-I project funded by MICIU/AEI/10.13039/501100011033 and, by \"ESF Investing in your future\". [PERSON] was supported by the ED481A-2023/086 predoctoral contract through \"_Programa de avudas de tapra producton da Xunta de Galicia\"_ cofinanced by the European Union within the framework of the FSE+ Galicia 2021-2027 program.  
The authors declare no conflicts of interest.