Quote Originally Posted by batwister View Post
They are pretty thick. There's an extra, thinner piece of glass that came with the enlarger, which I really can't get my head around. Obviously this doesn't sit flat with the thicker top piece and neither does it solve the reflection problem. My enlarger is a Krokus 3 by the way.

I'd be very worried about scratches to the negative with aluminium, even if I was extra careful filing. Isn't this a problem with yours?
Well I used a milling machine to make the masks, then file a bevel in the port for the negative and finish with 200, 400, 800 and finally 1,000 grit wet and dry paper. The file cut edges are as smooth as glass.

You can even use mat board to make a mask. it is just a bit fragile.