Hello Marlo, I have no proven answer to your query, but have certainly observed the same phenomenon, and thought about it some. All I can offer is my unsubstantiated theory. We do know of course that it is not merely a time-related change, because live-taken specimens with good transparency will retain their transparency for many years. So, it is apparently some external and fairly vigorous agent that causes the rapid transformation from transparent to opaque white. When you say "dead collected", you presumably mean "beach collected", probably in the "beach drift" or "shell hash" that is deposited near the high tide line - and that, I believe, is the key. A shell doesn't just ride in on a wave and get gently deposited in the drift line. Before it ever reaches that final resting place, it has been driven up and down the beach many times by the ebb and flow of the surf, each time tumbling along among millions of rapidly moving sand grains. Sand grains (in most localities) are largely quartz and other dense minerals, far harder material than the calcium salts of the shell. Consequently, the shell gets innumerable tiny (probably mostly microscopic) scratches all over it. The result (I theorize) is the same as you would get if you sandpapered a sheet of plexiglass, or even a pane of glass - a change from glossy and transparent to dull, opaque, and apparently white. "Frosted glass" is made by two separate processes - acid etching and/or sand blasting. I suspect that what we have here are "frosted shells" resulting from sand blasting. Hmm - that raises an interesting question - in areas where the sand is mostly of coral origin, are the microshells generally in better condition than in areas where the sand is primarily of rock origin? Anybody know? Paul M.