Just wanted to share a thanks and congratulations. You never cease to amazed with your content, knowledge and dedication to the site. If I may share a trick I have been using for some time now on the etching, aligning double sided toner, and positioning decals on boxes. I grabbed one of those digital picture frames from the resale shop for cheap. I only wanted the smallish backlight panel. I was able to power it with a wall wart. It is thin enough to put under my container of ferric chloride. With the light shining through you can see almost exactly when the etch is complete. I also use it behind the double layer of photo paper for 2 sided boards to align the art, it shows great through the vias. You can also position it under your box that is already drilled. The light will illuminate through the holes of the box and through the backing paper enough to position it on the box. Hope these tricks help. Look forward to many future conversations. Jeff
Another option for a backlight might be a led panel like the ones used for 3d printed lithophane panels. Don’t want to seem like an ad. I use the one from Bambu labs (search for CMKY light panel).
Excellent suggestions guys, thank you
Woodb180
If it is modern FR4 board, you can use UV-A (~400nm) LED, because it glows greenish color under it.
As of backlighting, I had good luck with old LCD monitors backlight. After switching fluorescent tubes to LED strip, it produces really nice uniform light.