However, when I investigated thermal expansion and contraction issues, a couple sapphire fabricators stated that they can heat the glass up to red hot and drop it in water without it cracking. They also mentioned another failure mode having to do with surface etching and surface fractures from the plasma. They have a very technical name for it and I can't remember what it was called. Do you have anything idea of this surface etching phenomena?

I at first time hear about influence of surfaces state on volume cracking. I have the own experiance: if sapphire to heat up to 300-500 C deg., and then drop in water — all volume will be cracking. The best surfaces qualty in micro-scale is “as grown” surfaces quality. This surface is atomic-smooth. Surface after polished to 60/40 is worse than “as grown” (in micro-scale). I don`t think that any etching is doing the surface better than “as grown” surface). I know this effect by heating 1100 C deg. (no cracking after heating and .... water) with SiC ceramics. But ceramics is not sapphire single crystal. Ceramics has the emptiness.

You can ask your fabricators to do the video of this process, but by this must be really sapphire crystals.

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