Thank you for contacting the Rakow Library. I have searched our literature and did not find a specific answer to your question about adhesives for repairing micro mosaic jewelry. There are several types of adhesives and glues used for mosaics, including craft glue, wellbond and others. I might suggest you contact one of the Mosaic societies for their recommendation or even a supplier. They would have the most practical advice.
Society of American Mosaic Artists: https://www.americanmosaics.org/
British Association for Modern Mosaic: https://www.bamm.org.uk/
Mosaic Matters. “The online magazine for all things mosaic. Includes a glossary of mosaic terms, notice board for questions about mosaics, pages of hints and tips. https://www.mosaicmatters.co.uk/
Suppliers include:
https://www.dimosaico.com/store/
One article about modern Italian micro mosaics had an interesting comment: "The adhesive was always the secret, made from a mixture of linseed oil, marble dust, time and maybe...a bit of wine!"
