Protective layer removal
Etched PCB is washed in water and dryed, then the copper protective layer is removed. If laser printer or nitropaints is used
for protector, it can be washed with acetone (or 1:1 acetone with water). If vinyl film used, it can be taken out with knife.
If photoresistive film used, it can be removed with alkaline solution (NaOH or KOH).
Etched PCB without protective layer is oxidising by air, and should be drilled and tinned as soon as possible. If you plan
tin the board later, you can drill through protective layer, or cover whole tracks with rosin after cleaning and/or drilling.