Homebrew PCBs

This may be an anti tarnish compound.  Many anti tarnish compounds contain 
amines that form very strong bonds to copper and often act as a base for 
adhering other materials.  They are commonly used in photoresist 
compositions to enhance adhesion.  Toner may (note I said may) actually 
stick better to an amine treated surface.  Amines are readily removed in 
acidic etching systems so they shouldn't cause any problems in later 
processing steps.