I have been following post with interest, even though I only use the Photo expose and etch method. (I have had consistent results with 2 layer boards)
As some members seem to be prepared to experiment with various solvents to achieve good and repeatable results, how about trying Brake Fluid?
As this substance seems to dissolve a wide variety of plastics, natural and synthetic Rubber, Car paints. (Including factory finishes! This method was used in the past, some "muppets" had daubed a bottle of brake fluid all over my buddy's car with really nasty results)
On a related topic using the same post heading; -
Has anyone used, or tried using a low power Extreme Ultra-violet (UAV) LASER (I cannot remember if it's 40 or 400nM) to expose the photo-resist clad board?. At the time of attracting my attention these LASERS were on sale at 45.00GBP!!!!
My set-up would involve a standard PCB CNC table with a "Qwick-Connect" adapter to allow rapid change of the Z-axis between Drill and LASER mounts.
I have asked about this topic in the past and received no response, but this was during a period of my account being hacked
chester