Mark, not an answer to your actual question but wanted to mention anyway: I use Weston Diploma for Vandykes, (+ Clerc's gold-thiourea toning) and for me it works great! (Just a note if you ever decide to switch to Vandyke...) I add 1-2 drops of 40% citric acid into the coating solution (not to the stock sensitizer!), makes it work better; great dmax and tonality + zero fogging...

Regards,
Loris.