Hi, I've been trying to make some vdb prints during the last couple of weeks. I develop the print in 1% tartaric acid solution. After about 1 minute black spots appear on the edges and start to grow in the fully exposed parts, but occasionally they go into the picture. After fixing the black is washed away forming a light spots. I can't seem to find what may cause this. Tried it whit whit different papers, developing with tap water or tartaric acid solution, one or two layers of vdb solution and the result is more or less the same. I'm attaching some pictures. The first one is just before the border becomes black, and the second one is a minute later with a black border. Hope someone can help. Thanks.