I recently came into possession of two large (approx. 3x4 ft) copper-clad fiberglass boards from a junk sale. These boards are consistent with typical printed circuit board material (thickness, flexibility, internal appearance, etc.), save for a blue coating on both sides. Here are two small pieces I cut off for testing:
Here I've sanded off some of the coating to reveal the copper underneath (the cuts are from me testing my PCB mill):
The copper is conductive (unsurprisingly), and the coating is not.
Any ideas on what the coating might be? The boards are probably around 5-10 years old, and were covered in a thin plastic sheeting when I obtained them.
Specifically, I'd be interested in knowing (a) how to remove the coating without damaging the copper (solvents? acids? photoexposure?) and (b) if I could use the coating in some way to help make printed circuit boards (as a resist material? ablate with a laser cutter?).