Chris,
I did not clear this test strip, I could do it as well.
I have been flashing my gums for 2 to 5 seconds routinely now depending how dense my negatives happen to be. Even on the test strip you can see the much more delicate gradation in the highlights. Almost like printing in palladium.
This really shows in tri-color gum with the cyan layer, which defines most of the contrast and tonal gradation.
I have just finished a family portrait that I have done flash and no flash version. What a difference in the skin tones that additional flash exposure delivers. Will scan and post later tonight.
Eliminating the stain delivers brighter, more saturated colours as well.
Marek
Date: Tue, 9 Dec 2008 08:16:25 -0700
From: zphoto@montana.net
Subject: Re: Extending gum range and the tone reversal.
To: alt-photo-process-l@usask.ca
Thanks for this Marek. It is always heartening to see someone else testing things for the heck of it and you are the test King! Bleaching, pinhole, yupo, solarization...
I love how Picasa has that magnifying glass option so we can really get close in to the test strips. Almost like being in your dimroom.
I like also how you can see on your wedges where the numbers are dull with too little exposure.
So do you think you will use the flash technique in your practice in general or only with dense film negs?
One question: did you clear your step wedges in potassium metabisulfite or whatnot? It can be hard to determine how long gum's tonal range is at times because of the fact that the dichromate gets darker and darker and darker with exposure and gives a bit of a false read to the step wedge when, in fact, gum has reached "max black" before the dichromate has reached "max brown". I don't ever clear unless I am doing step wedges. I find that gum has a 4-6 stop range, with 6 stretching it. This is certainly longer than some books that say it has a 2 stop range, though, and it looks like from your step wedges you are getting more like the 4 stops. Do you find this to be the case in general? I'm including max black and paper white in the range as steps (wanted to clarify because some don't include paper white).
Off to work, though I'd love to have this convo instead...
Chris
__________________
----- Original Message -----
Sent: Monday, December 08, 2008 10:55 PM
Subject: Extending gum range and the tone reversal.
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
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