U of S | Mailing List Archive | alt-photo-process-l | Re: Exposure times in tricolor gum

Re: Exposure times in tricolor gum

On Nov 18, 2008, at 11:19 AM, Katharine Thayer wrote:

I haven't followed this entire discussion, but if the question is about differential exposure times and curves for tricolor gum layers, my informal experience from years of printing tricolor gum in an intuitive rather than calibrated fashion was that the exposure times were essentially the same for all layers, and my observations from a recent year or more spent carefully studying the calibration of digital negatives for gum have yielded the same conclusion, that there's not that much difference between them.

When determining exposure times very precisely for printing PY97, PV19 and Prussian blue on Arches bright white, gelatin-glyoxal, the exposure times were Prussian, 3:00; PV19, 2:45; and PY97, 2:15. In other words, not that much difference, but the yellow was shortest and the cyan longest, not the other way around, and that's always been my experience; when there's a difference it tends in that direction.
Since there's been some discussion about the relationship between exposure and development, I thought perhaps this could use some further explication.

During all the years when I was printing tricolor by a sort of intuitive understanding of how it all worked, it's possible that while I was exposing each of the colors the same, I may have been developing them different, because I didn't pay much attention to development times per se; I just developed until the thing was "done."

But where I talk above about "determining exposure times very precisely" during the time I was calibrating negatives for gum, that was with the devepment held constant. How else would you determine precise exposure time except by reference to a standard development time? The times I report above for Prussian, PV19, and PY97, 3:00, 2:45, and 2:15 minutes, were determined for a standard development time which didn't vary across the colors; in other words, the rankings of the times are not affected by a possible difference in development times.