Homebrew PCBs

I have been using tracing paper (Vellum?) and a laser printer to produce 
transparencies for photoresist. I have some good results, but the large 
dark areas tend to be less than opaque having a speckled appearance 
which tends to be reproduced on the copper. I was reading about some 
spray cans which supposedly darkens the toner pattern (Toner Aide and 
Casey's toner darkener). Unfortunately I can't find a supplier in New 
Zealand and if I could it would probably be around $30-$40 a can. 
However they appear (from their MSDS sheets) to be a mixture of solvents 
sprayed from a can so I mixed some Acetone and Ethyl Acetate and sprayed 
this on the transparency from a small mister spray bottle I had. It 
worked, although the vellum curled up a little.