Blackout cloth is used to line curtains to block the light so you can sleep in on a sunny morning. Blackout cloth is white or cream colored; it’s not black like you might assume.
A friend had cautioned me about being sure to not get anything translucent as he had some strange effects from his screen where the image was reflecting from the wall and back through his screen. Even without that, any light that penetrates the screen is not coming back to the viewer and is wasted.
I beamed the largest in focus image I could on my wall and measured. I got 8 feet of blackout cloth (it’s was 54 inches wide), three 8 foot 1x4s and a 2×4 foot piece of light plywood.
The plywood was cut into four triangles. The 1×4’s were cut so they fit together to match my measurements and screwed together in a rectangle using the plywood triangles on the corners.
I spread the fabric out on a clean surface, coated side down and carefully lay the 1×4 frame on top of it. I wrapped the fabric over the frame, stapled it to the wood and trimmed the surplus fabric. To mount the result to the wall I used small angle brackets; they were screwed into the wall in line with the top and bottom of the screen, then I slid the screen in between them and screwed directly into the top and bottom of the screen so the brackets were concealed.
I’m very pleased with the results.