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Unfortunately, it is very possible. It's called "silvering". Yes, the resin is hard and you would think there's no where for bubbles to move, but it happens with organic specimens that were not properly dried because as they dry, they shrink (even if miniscule amounts), which creates room for the bubbles to occur. It doesn't matter how fast the resin cures; what matters is the moisture content of the specimen at time of encapsulation.Often, silvering may not occur for months or even years after encapsulation. It might never occur at all, with luck and smaller/drier insects. But it does happen, and the fact remains that if it does, there's no way to fix it because the resin, acrylic, or other hard substance used for the encapsulation has already cured.