About 18 years ago, I was having problems with certain glass colors consistently cracking their encasement’s. The colors that were the most problematic were; Italian Opalino’s, all the pastel reds, yellows, oranges and browns. This was such a frustrating problem that I would ask everyone who did lampworking the same question. “How do you keep these problematic core colors of your bead from cracking the encasement”?
The answer came from a to-remain-un-named Italian lampworker, who happened to call Frantz Art Glass for a price quote on gold foil. When he was asked the encasement cracking question, he said “Everyone knows the answer to that question”!
Much to my delight, his complete explanation was spot-on for solving most of the cracking problems I was having and this is what I learned.
If you are using one of the glass colors that is cracking your encasement, put a core of clear glass around the mandrel before you lay down a thin skin of the problem color to make the core of for the encased bead. The clear glass expands and contracts better with the metal mandrel and the fact that you are using only a thin skin of the problem color, lowers the chance that the encasement over the bead core will crack.
This technique has been especially useful when I use dichroic on clear sheet as an encasement because the dichroic crystals make the bead even more likely to crack with the problem colors. I describe the dichroic crystals as an added irritant to the molecular integrity of the glass bead.
If you are having problems with the core colors cracking your encasement, give this technique a try, it really works!