Lostfocus, just drop the practice of adding dichromate into the coating solution; see this for an effective method of contrast control:

http://www.usask.ca/lists/alt-photo-...aug02/0368.htm
(Thanks much to Liam Lawless and Sandy King for researching/testing and making this information available.)

BTW, I would try to find ways to increase the negative DR instead of fiddling with the emulsion formulation; Vandyke works best unaltered.

Regards,
Loris.