Ditto the comments above on long burning in times / reflective surfaces around the enlarger. I saw pictures of Harry Callahan's darkroom once, a simple and unglamerous arrangement, but what I remember was a large black cloth draped or attached to the wall all around the enlarger - no painting of walls necessary, although watch out for dust (choose the fabric wisely). Also, burning in tools, like cards, etc should all be black, at least on the bottom side to avoid reflections up off of the print and back down again during the burning in process. To compare - do a test strip twice with the card a couple of inches off the paper, one with a white card, one with a black card, process together, you will see the difference.