At last, a problem with a solution. When we first started coating paper with our own cyanotype chemistry we were getting bad yellow stains. It turns out there are two ways to combat the ugly yellow. One is to add citric acid to to the first water bath when developing the print. The easier way is to add a bit to the sensitizer chemistry itself. We'd done that, but it turned out we hadn't been adding enough. So now, the yellow you see in the above print is a thing of the past. One problem solved, eight zillion to go.