Quote Originally Posted by kintatsu View Post
I'm using a red light of relatively low intensity. I just tested it by placing a coin on the paper, and leaving it sitting out for a minute.
Just to confirm. This red light is red, not dark-orange, and that it is a safelight not a random red light-bulb.

To do a fairly certain check try the following. ...

With ALL lights out, expose a strip of paper under the enlarger to something that will give a very light grey colour when developed. Turn on the "safe"-light. Cover half of the width of the strip length ways with a piece of black paper. Place four coins overlapping the printing-paper and black paper -- this setting up should be done in a few seconds and in the brightest working are of the darkroom. After two minutes remove one coin, repeat until all the coins are gone, then do a last two minutes. Develop/stop/fix/wash the paper.

By comparing the covered and uncovered sides of the test strip, and the locations of the coins, it will be easy to see if there are any visible shapes whatsoever. If the piece of paper is not perfectly even in tone then the darkroom is not safe. Reasons could be light-leaks, un-safe safelight, or even indicator lights on electrical sockets etc. The test starts on a "grey" tone in order to get above the threshold of the paper.

When you sort things out so that ten minutes is ok (five times two minutes) then you can be confident that normal efficient paper handling will not give a problem, and then test for longer!