If like me you don’t have the luxury of a permanent darkroom then the problem of making the darkoom light-tight is a big one. No need to buy expensive photographic blackout material or blinds though as there is a much lower cost and much better material easily brought from good curtain shops – 100% opaque curtain blackout lining is perfect. Made for night workers or people who just can’t stand the light from passing traffic.
It doesn’t cost much, it comes in big widths and can be cut with household scissors without fraying, it is white so the window isn’t weird looking from the outside and the hot sunshine is reflected away.
I had the curtain shop make a neat professional job and sew on velcro edges which marry discreet self adhesive strips on my window frame. In point of fact I have a second piece of material which I hang like a roller blind on the inside wall which is longer and wider than the window aperture, it is an extra precaution so I have no worries about light creeping around the edges or the velcro strips peeling apart. To make the door light tight I simple tack with drawing pins a length of the material from the top of the door frame, it is heavier than normal cloth and hangs nice and flat.
To test your darkroom is totally light safe place a coin onto photographic paper, leave for five minutes and process. Any fogging will reveal a whiter circle where the coin covered the paper. If you can see where the coin was make sure the problem is not the darkroom safelight rather than day light getting in.