Ok thanks for the detailed description. Can you please try once more w/o blow drying the paper? Just coat the paper, let the sensitizer set until the surface becomes matte - takes 5-10 minutes (15 max!) depending on the humidity of your studio - and then hang the paper and wait further to complete 45 minutes total drying time and expose that way. From your description, it looks like the mottling was caused by (force) drying the paper blowing from the back, resulting a paper with uneven moisture content. *Let the paper dry in peace!* (Edit: Or, if you feel like you absolutely have to use the hair dryer, then blow both the back and coated sides of the paper.)
BTW, I personally don't prefer exposing bone dry paper with Vandyke; you get a much better dmax (and speed) with some humidity in the paper...
Let us know how it goes and good luck!
Last edited by Loris Medici; 06-01-2012 at 02:33 PM. Click to view previous post history.