Not at hand, but they are 1/2” plywood with simple routed grooves on hardwood runners. Two of the three have little 3d printed, scalloped pen “trays”. The third is deep enough for most brands of 50-60 mL ink bottles.
The back is just hardboard set into a rabbet, so this thing looks neat against a wall. It’s also heavier than it looks, lol, and with plenty of, umm, “character”.