"Tesserae" is a term for any object used in creating a mosaic; for instance, vitreous tiles, stained glass, found objects, ceramic tiles, smalti, etc. Here's an overview of some materials you can use in your mosaics. Read all about it.
Making a mosaic with a mirror is so fun and they turn out beautifully! Especially on a Skeewbacker. Here's some help for getting your mirror placed just right onto your Skeewbacker.
Wood backers (substrates) will not last nor honor the heritage of mosaics. The reason - the 3 destructive properties. Learn why you should never use wood for your mosaics.