Charlie+ wrote:
On Thu, 21 Feb 2008 10:11:57 -0800 (PST), Christopher Tidy
wrote as underneath my scribble :

I had a microscope with a ~45 deg semisilvered mirror that needed replacement,
tried a standard mirror but turned out it was a "cold mirror" and removed IR
from the lightpath to save IR from the users eyes (multicoated so IR passes
straight through).
Be good idea to find out the original specification....!?
C+

The best that will be possible is to look at an original reflector. To
the best of my knowledge, W. Watson & Sons are no longer in business.

Best wishes,

Chris