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 out a towel, sprinkle a few grams of 500-grit silicon carbide on the glass, and spritz a little water on top:
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.
After about 30 minutes of grinding, washing, checking, and grinding again, I end up with a very smooth, even screen:
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.
Next, I trace the old glass on the new, and lay a straightedge on the new screen:
Even pressure on the cutter, snap on the edge of the table, and you have a clean cut:
The final screen, with clipped corners:
You can see, side-by-side, just how much finer the new glass is than the original:
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.