Last Updated: Jan 09, 2017 Views: 282
The film you describe is caused by the atmospheric deterioration of glass, known as "crizzling" or glass disease.
A few pages from Stephen P. Koob's book, Conservation and Care of Glass Objects, 2006, pp. 117-120 are very relevant. Koob explains why some glass crizzles and describes the initial stages in these pages.
I checked with Mr. Koob (who is our Conservator at CMoG). He added that we don’t use the word “oily”, but “slippery, slimy" feel. "It’s the alkali leaching out, so it’s slippery like soap (another alkali)."
Please let me know if you have additional questions.
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