The dye I use for this process is liquid black Rit dye. I am going to use the products above to test out different colors. The bottle on left is liquid dye (obviously not black, I don't have that container anymore). The two boxes are powder dye that you're suppose to mix with water. Until I test them out I can't say for sure how they will compare to the liquid dye but I suspect they will perform similarly. When I test out the blue, grey, and white colors I will post the results on this page so you know what to expect if you try out these colors at home.
I would recommend doing this either on a surface you don't mind getting stained or very carefully in your kitchen with plenty of paper towels at hand. I mix a whole bottle of liquid dye (236ml) with about 2.5 liters of water. The dye can discolor the pot so you may want to use an older one that you don't mind sacrificing.
A rack is necessary for this project, I just use one I built out of K'nex. You just want to make sure that the flat pcb board doesn't sit flat on another surface (like the bottom of the pot or another board) or the dye solution won't properly penetrate the substrate.
After you put the rack and boards in the dye solution cover the pot and simmer (about medium heat) for 30-45 minutes. Keep an eye on the solution to prevent foaming, it is very messy when you have a concentrated black liquid dye solution boil over. After the 30-45 minutes is up turn down the heat to low and let the solution sit for 2 hours. After the 2 hours are up turn off the heat and let the cards sit in solution overnight. These instructions produce a very dark color, if a lighter color is desired heat the solution for a shorter duration of time and/or at a lower heat.
After you have let the boards sit in solution over night remove them while wearing gloves to prevent staining of skin. The boards will have a somewhat gelatinous coating on them. Do not discard water dye solution the mixture can be used repeatedly. The mixture also stores very well, I have used it again after putting it in a sealed container for 6 months.
Fill a glass bowl with water (glass to prevent staining a container) and submerge the boards in water and scrub them with a soaked paper towel. Remember to scrub all edges of the boards to remove all excess dye.
Rinse off boards in fresh water and dry.