Well, what I thought was spray-on frosting turned out to be just a really, really bad screen. Rather than grind away on it for hours to remove all the micro (and mega) chips, I bought a 10×12″ sheet of single-strength glass at Ace Hardware. $3.49 well spent.
I lay the lapping glass on top and start grinding in a circular pattern. I’ve done a lot of these glasses, and what I’ve found to be the trick is having just the right amount of pressure on the lapping glass, and just enough water to keep the grit from drying out completely. Too much pressure, and you cause the micro chips in the glass that create annoyingly harsh grain. Too little pressure, and you’re not grinding. Too much water, and the lapping glass floats. Too little, and you scratch the glass.
You’ll notice that there are a few major low spots on this glass that haven’t been ground yet. Luckily, they fall in the waste areas. Otherwise, I’d continue lapping until the glass had been worn to the lowest level, creating an even grind.
So, the ground glass is finished. Next will be stripping the ground glass frame, regluing it if necessary, refinishing it, polishing the brass, and lacquering it all.