I wondered when someone would spell out the real solution. Been reading all the replys and taking it all in. Myself i have used the 3M buffing compound with much success. I can remove a glass from the field and bring it in the shop. Place it on the foam covered horses and scrape all the black stuff off the edges with a razor. I promote the desolving of this stuff with laquer thinner then wipe the excess off. I then squirt on some 3M buffing compound and go to work on it with my Dewalt variable speed buffer equiped with a foam pad. This does an excellant job. Be aware that they make various grits of the buffing compound and i use the final glaze. Comes in a black plastic bottle at your local body and paint store. Try this next time.
Small Block