Today we completed the first stage of our mosaic reproductions using the Ravenna method. We had embedded the tesserae onto a lime substrate, a temporary binder that keeps the tiles where we had carefully placed them. The nice thing about lime is that it takes a few days or longer to completely dry out, giving the mosaicist plenty of time to complete this step.
Before transferring the mosaic to a permanent binder (in this case cement), the front of the mosaic is covered with a damp cheese cloth before being sealed with a glue. Once the glue dries, we will scrape off the lime backing, lift the now hardened cheese cloth and put the whole thing onto a cement bed. Then, we will dissolve the glue wash and scrub the mosaic. Voila! (later on we will get to the Voila! part)
The icky part is that the water soluble glue we are using is made from rabbit bones and skin. It comes in small amber colored beads; these are melted over a double boiler before being brushed onto, or rather into, the cheese cloth. The smell is nauseating, and the thought of spreading boiled bunny bones over my mosaic made me want to puke (but, I rarely vomit, so this didn't actually happen). Apparently rabbit glue is also used for other restorations - of violins, frescoes, etc. I was briefly consoled by the thought is that at least all of the rabbit is being used - the rest of it you can find on menus in Italian restaurants or in jackets.
I asked about non-animal glues that could be used for this purpose. There are substitutes (such as a heated mixture of water and flour) but each of the animal-friendly versions comes with limitations, either drying very slowly or requiring extensive cleaning afterward. Luckily, there are other ways to make mosaics, using materials available at Home Depot. These are sticky, just not icky.