Just a quick thought, and not even directly related... I used to do photography & astrophotography back in the days of "hypered" 2415 technical pan and other B&W processes. Since I was taking general chemistry at the time, I had an interest in the various developers available at the time, and how they could be used to alter the recorded image.


One of the developers I used had some interesting properties. It was recommended for fine grain detail, and had a developing agent as well as an agent that eroded the developed grains, and rounded them off. (I think it was HC-110, but it's been too many years...) This provided smooth round grains that enhanced fine detail. By varying the development time, you could alter the effect of this second agent.


So... PCB photoresist is likely a completely different process, but may use the same concepts and methods. Your fine traces may have been eaten away by over development.

Just some speculation on my part.


Rob