Tom M wrote:

snip

No, these are semi-reflective. They are not absorptive. If you contact me
via email, I will send you a picture.

I'll send you one for nothing if it will work. They are 0.060 thick and 50 x
50 mm square.

Thanks for the offer, but I discovered that the design is intended to
use plain glass. I called a few glass suppliers and couldn't find a
piece the right size. In the end I found another identical microscope on
eBay cheap. It has a few issues but with the pair I'm sure I can build a
working microscope.

Nevertheless, thanks very much for the offer.

Best wishes,

Chris