Hi Don,

this layer is printed on in near liquid form and then BAKED at almost 200
¡C, almost the same way as a car body paint job. So it is altered
chemically to withstand the stress during the soldering process.
So far I have not discovered a solvent for this thing. But if you heat the
PCB to more than 100 degrees, the layer will become easier to scratch off.
I don't know any other method if it's industry standard stuff..

Greetings

Jochen DH6FAZ