I'll try answer a couple of posts here. First, Moretti/Effetre Opalino glass is not quite compatible with the other glass of the series, and some, the Carnelian for example, is particularly incompatible. Therefore, mixing this glass with others is likely to produce a bead that is not durable. One series that I made that used ONLY opalino glass, but mixed a green base with small amounts of rose and white, cracked, even after being well annealed. The first cracks took about a month or more to begin showing, and many of the other beads began indicating cracks over the next six months to a year. After the first 18 months, the rate of cracking declined to zero and I have had no beads in the batch crack since. But, I lost more than half the beads from the batch to stress cracking. Will the others crack over time? I don't know, but it is very possible. By the way, these beads were made over a period of about a week, so it was not an error in any one session that contributed to the problem. There were about 50-60 beads in this particular sample.
On the other hand, I have used the Nile green as a core for beads that were multiply cased in various transparents, and those never showed any cracking. In this case it was the proportion of glass that kept it from happening because the Nile green formed only a small core completely surrounded by large amounts of glass that overcame the small amount of stress in the core. It is the same characteristic that allows one to make a paperweight with Moretti constructs in the interior and then Schott S8 as the encasing glass. There is indeed stress, but it cannot overcome the strength of the surrounding glass and cause a crack.
As for whether or not one can predict that a bead will or will not crack, I don't think there is any way to do this. If the bead is transparent, you can use a polariscope to examine it for stress. If it is opaque, you probably cannot tell. The real problem is that cracking does not follow a schedule, and may happen at any time. The best way to create durable beads is to understand the characteristics of the glass one is using, to use sound lampwork techniques, and to properly anneal the resulting bead. There is no magic, just sound craftsmanship.
The beads that I currently make from opalino no longer crack, but I am careful to avoid those things that I know increase the probability of them cracking. The rules are still the same, practice, practice, practice, and learn from your mistakes. I make lots of mistakes.