All
A few weeks ago I was printing gum from a negative that was way too dense. It was not my nagative, so I really could not do anything with it. When I printed a thalo blue layer I noticed a tone reversal and a heavy stain in the highlights. I typically do not encounter either as my gum negatives are not that dense. This was an opportunity to learn so I printed some step tablet tests and determined that indeed a little exposure was needed or else a "tone reversal" or heavy stain resulted in the test prints.
That prompted me to add some 'flash' exposure, no negative in my UV box. I am posting a test printed with thalo green, one of the most staining pigments. I had a test strip with thalo blue and indanthrone blue, but can't find them now.
On the test strip there are 1, 1:30 and 2 min exposures. You can easily see the tone reversal on the 1 min exposure where the number 21 is much lighter then say 8. I also posted RGB readings to illustrate the stain. I wish I had done a 4 minute exposure as well, next time I suppose.
The center 3 strips are 1:30 second exposure with 2, 5 and 10 second post flash with no negative. Steps 1-7 are visible on the print, maybe not quite on the scan. There is also very little stain and no tone reversal. this is a remarkable density range for gum. This was all printed and developed on one piece of paper to have the development constant.
I have been printing with a flash for a while now. This really opens up the highlights, but requires somewhat denser negatives than typical gum.
For those ready to experiment I would suggest using step tablet and not existing negatives to test this idea.
Always something new and exciting with gum.
Marek
just one picture http://picasaweb.google.com/marekmatusz1/ExtendedGumRange?authkey=AKZxcCQlqts#5277658299253953138