Yes, shells do have a tendency to crack when heated to high temperatures. However, a few years ago I experimented a bit with destruction of pigments by heat, and I found that cracking is minimized, and usually avoided, if you (1) place the shells in the oven on an asbestos mat rather than a metal or glass surface, (2) place the shells in the oven before turning the oven on, and (3) turn off the oven when the baking is complete, and allow it to gradually cool to room temperature before opening the door. Shells which are light colored to begin with often come out pure white. I had no problem turning Oliva reticularis into Oliva olorinella, or Cypraea miliaris into Cypraea eburnea. Areas of dark pigment usually do not come out white. A Conus marmoreus came out with its formerly black areas an orangey-tan color. A Conus textile came out looking like an albino when dry, but the original pattern could be faintly seen when the shell was wet. I don't really think that the manufacture of "albinos" in this way is much of a threat, but it doesn't hurt to keep the possibility in mind before paying a premium for an albino specimen. Paul M.