Apparenly around 2009. I bought a new bottle (plastic now vs. the older
metal), and am truly dissapointed because IT NO LONGER WORKS.

The formula is water-based with ammonia, vs. the old petroleum-based
formula. The new stuff appears to have the micro silica granules because
there did appear to be major sedimentation in the bottle. It is no longer
listed as an ingredient, probably because it is not toxic.

I'm not sure if they changed the granule size, but the new product does NOT
immediately produce black copper oxide the same way as the old formula.

Of course, my goal here is not simply to whine. Altough whining is a
component of the set of my reasons for being here, I would also like to ask
if anyone knows if a suitable substitute in available. Is it also possible
to buy microcrystalline silica (or carborundum, etc.)? I have Varsol, and I
know how to use it.