strange results, aj please respond

i got different results from the same pill because i tested it once on a plastic surface, and it was pretty much clear, but when we tested the same pill on an aluminum surface, it turned red for speed. any ideas?
thank you.

Glass is good to test on.
It will not interfere with the reaction (that's why the test is in glass as well).
That stuff what plates and wash basins (and bath tubs) are made of, you know the hard white stuff (damn, what is the english word ??) is good to test on.
Avoid metal, it will interfere. Avoid paper (especially if it has something printed on it).
So, glass is definitely OK and all those white surface in the bathroom are OK ;-)
(Can someone help me out with the word for that white bathroom stuff here ??)
Rgds
aj

porcelain? ceramic?

Ceramic !
Yep, try it on a ceramic plate, that does not interfere with the reaction ;-)
Thanx
aj

I use a piece of white ceramic tile. You can cut a small piece to carry around if necessary.

hehehe i can just see it, arrested for possesion of drug paraphenalia: one piece of ceramic tile....