Hi I have a Brownie camera that the red sight glass is broken out. Is there some type of red translucent plastic or film that I can cover the hole with, so I can see the numbering on the film? Also I have an Agfa Clack with the same problem.
automotive tail-light lens repair tape, some rosco film, or maybe just some black tape that you peel up to look at the numbers then stick back down.
That it's red doesn't do anything for you if you're shooting pan film. And, at least for Kodak and Ilford films, the backing paper will protect the film.
Try to locate an art supply store that sells small individual sheets of Dead Link Removed masking film. Cut out small pieces and stack as many as you can over the opening while still being able to read the frame numbers.
Note also that on my Brownies I still cover the red window with a piece of black opaque photographer's tape between frame winds, just to be safe.
This stuff is very inexpensive. If you can't easily locate any, send me a private message (PM) with a safe postal address and I'll send you a small sheet.
I was also going to suggest Rubylith. I remember it from the late 1950s. Printers used it. My first camera was a Brownie Reflex and I have a "new" copy of that model that I need to take out for a spin one of these days. It took better photos than many people might assume.
I got mine at Dick Blick as well. I seem to remember they were the only ones I could find selling sheets instead of rolls. A couple large sheets are probably a lifetime safelight filtering supply for me.
That's why I offered to just send the OP a small piece. Brownie red dot windows are awfully small to be cutting from a 20"x24" sheet...
Perhaps if we knew for which brownie the window was needed or the approximate measurement for the window, there might be some other suggestions. I have a brownie or two that might be able to be donors with a little more information.
Get a slide film, shoot a couple of frames aiming at a uniform red surface (chose the apropriate tonality of red), and enjoy the rest of the roll aiming at your favourite subjects. The red slides can be cut as you want to replace the red-window.
Regards
Joao