Tuff Break is the name of “That Rubber Stuff” for setting enamels. Several reasons why this product is great.
One, Tuff Break adds protection to the counter while setting enamels. How you might ask, by giving the enamel piece a cushion, that rubber stuff, against the metal as you are pushing to close the bezel over the delicate enamel edge. After many firings, one needs to be gentle while setting enamels.
Second, that rubber stuff removes that clingy sound of the enamel against the metal once the piece is complete.
Many enamelist use types of glue or a piece of plastic behind the enameled piece and even sawdust in setting enamels. I feel this adds a more professional element to the cloisonné jewel.
See my setting cloisonné enamel jewels https://alohilanidesigns.com/setting-cloisonne-enamels/ and you will get a better picture what I an sharing here.
You can find Tuff Break on Croft Kiln site http://croftkilns.com/accessories/