um Dancesafe are great, dont get me wrong BUT their pill database cannot be used as empirical evidence in this, or any other simliar case.
according to the
"US National Institute of Justice...Color Test Reagent/Kits" Phencyclidine (PCP) will give no reaction to a Marquis reagent test. It will also, apparently, give no reaction to an E2 or EZ Test Supreme. Possibly the only reagent which will pick it up is the Cobalt Thiocyanate reagent(Coke Tester).
so why did Dancesafe say they got a "slow change to black"?
my theory is that the pill they tested had once been stored in a baggie with other pills, some of which were MDxx. this put enough MDxx dust on the pill to give a "false positive" to the reagent test, but probably not enough to significantly register on the lab test.
or perhaps the knife wasnt properly cleaned that scraped the pill, or the surface it was tested on wasn't washed properly...
Dancesafe uses (relatively) untrained volunteers, who work in loud, crowded, distracting environments. I'm not hassling any of them for maybe screwing up a test or two, because I do the same work they do and understand how hard it is. and anyways, the testers were sufficiently worried about the reaction to forward the pill onto the lab for full testing.
My point is dont make assumptions based on limited, unreviewed data. this is very bad science. even if you had only used the data available in the Dancesafe database you would have seen that many of the few other pills that contained PCP gave no reaction at all.