I've been trying to do more testing before resorting to step tablets and thus kept testing for longer exposure time, while shortenning the distance between the tubes and the print.

Finally I shortened the distance to about 1.5 inches and exposed for 2.5 hours (see the attached, the right side covered by Pictorico Ultra Premium OHP Transparency Film). The result that it's still far from being dark is driving me crazy.

Can anyone give me some advice? Would a step tablet make a difference? I really don't know what to do next. Longer time would lead to solarization, as what the four-hour strip showed. And isn't it unreasonable to expose a print for several hours?

Thanks and sorry for my ugly brush strokes

PS: The paper is Bergger COT320, prewet for ten seconds before coating. a Hake brush. 6 drops FO+6 drops of palladium solution for an image area of 4X5 inches.