I changed to Ziatype from the B&S Na2 Pt/Pd system just over a year ago and I had a problem trying to determine correct exposure user a Stouffer step wedge.
Using 100% LiPd with no sodium tungstate or contrast booster I got a time of 12 mins with ‘traditional’ exposure steps but even after an hour exposure with a Stouffer, the steps had not merged. Going beyond 12 mins did not improve the dmax at all.
Adding sodium tungstate to warm the image needed dichromate or Part B to boost the contrast but the exposure times rocketed for both and I never got a good dmax.
I now use CsPd to warm the image (33% for neutral and 50% for warmish tone), with exposure times 14 and 18 mins respectively and both without contrast booster. However, very small changes in the moisture content of the paper before exposing will swamp the effects of the CsPd.
As Keith says, different curves are definitely required for each variation of chemistry.
To avoid the use of contrast booster (for digital negatives), two things are essential:
- Use a Piezography system with Photo Black Shade 1 or denser - I wasted so much time trying to get paper white and good dmax with an older Piezography system that worked fine with Pt/Pd
- Use Bostick & Sullivan products - Ziatype chemistry available from Europe doesn’t give as much contrast as B&S, as I found out to my cost.