One of the reasons I enjoy joint sessions is the more focused theme and connection between the talks. Laura provided a nice overview of the research that she carried at out at SAAM on marble coatings. Three white marble sculptures in the collection- by Rinehart, Cooper, and Houdon- attract a lot of attention and love from the public. Some love comes in the form of red lipstick. Laura took this as an opportunity to explore traditional and newer materials for coating marble and determine which have the best protective properties.
Her testing methods appeared thought out and well carried out. She tested Cosmoloid 80H wax and Ketone N resin, Renaissance microcrystalline wax, Methocel A4C Methyl Cellulose, and Avalure AC 315 Acrylic Copolymer 5% and 7% in ethanol. She tested polished and unpolished marble. All the coatings were applied by brush. They were tested for their appropriate aesthetic properties, effectiveness as a barrier, safe application and removal, reversibility and aging. Quite a feat if I say so. Needless to say there is more testing that can be done. However, her initial findings are quite interesting. To measure changes in color and gloss Laura used a Spectro Eye spectrophotometer and gloss meter. The marble samples were stained with lipstick, red wine, and a sharpie. Laura provided a nice graphic showing her samples and the order of testing, aging, cleaning, etc.
Overall, from the testing Laura concluded that none of the coatings were perfect. There is a give and take with all. However, most importantly Renaissance wax was NOT a good barrier- I found it shocking that the red wine etched the marble through all of the coatings except Avalure. The wax resin and avalure did the best in the aging test. Methyl cellulose had the best reversibility, while microcrystalline wax was the worst. It was also interesting to hear that the colorimeter readings were consistent with what she observed by eye. Although nothing can replace scientific readings it is nice to know that our trained eyes are good for something. She also felt that more research should be done on methyl cellulose and Avalure since they tested tested so well. Her tests were only done on small samples, but the practicality of applying it to a large sculpture might change things. Avalure is somewhat difficult to work with, but perhaps a spray application would be better. By the way, Avalure is available through the manufacturer and apparently they are generous with their free samples.
I don’t know if this would be possible, but a follow up to this study might be interesting to look at the penetration of these coatings into the marble. Perhaps looking at a cross-section with FTIR-ATR…