What is this treatment called?

I accidentally came across the name of this treatment while browsing through antique glassware books at the used book store - I wrote it down, but I can't find my note! It's a drizzled white pattern that is baked on and won't scratch off.

It's black amethyst, although it is VERY black and takes quite a bit of light to see the purple. I don't think it's the L.E. Smith loving cup as it doesn't have the dancing nudes and the base is round, but otherwise it is the same shape and size.

Can anyone help me? I've been searching online forever and I just can't find a thing - only one other person who doesn't know what it is either.

Thanks!

Cynthia