Thanks for your thoughts, Enthalpy. I'm still searching around for a reference on acid etching of CdSe but can't find one so far. If selenium etches faster, this may help explain our results, which otherwise are rather perplexing. But I've always said that experiment beats speculation any day of the week so I bought some bulk cadmium selenide and we're going to let it sit in some dilute acid for a few days, filter, and analyze the filtrate by ICP and see whether we have more dissolved cadmium or selenide. I'll report back.