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I've made some succesful prints now but no relief. To change my technique to maximise relief I plan to change a few things so could someone tell me if my assumptions are correct:
Going to a thicker carbon tissue (0.9mm) so reducing pigment about 25%
Need weaker gelatin in Glop to get max relief, so dropping to about 8%
Thicker tissue needs weaker sensitiser... say 50% of normal
Transfer onto Yupo
Am I correct?
Bruce (having fun experimenting)
I had similar problem with no relief visible. The solution was to lower pigment concentration. Now relief on wet photo is very visible and still visible when dry.
Lower pigment concentration means tissue can be penetrated deeper with UV.
I now believe this to be wrong after reading some more.Quote:
Originally Posted by brucep
I found a reference from the early 1900's saying that for relatively strong reliefs I need to increase the amount of Gelatin.
I will get there!
Bruce, it is a balance of several factors. If you have a negative with a density range of say 1.8 and a tissue that has 8 grams of pigment and a 8-10% gelatin and transfer to Yupo you should see relief. All other factors have to be in balance as well. Good luck!
To understand and demonstrate for yourself the relationship between pigment loading and relief will require that you hold several fields constant. The constants are, 1) negative density range, 2) gelatin type and percentage solution, and 3) method of sensitizing. If you do that you could potentially have the following three scenarios that will all work.
1. Tissue poured to wet height of 0.5 mm, with pigment loading of 2%, plus 20 grams of sugar.
2. Tissue poured to wet height of 1.0 mm, with pigment loading of 1%, plus 40 grams of sugar.
3. Tissue poured to wet height of 2.0 mm, with pigment loading of 0.5%, plus 80 grams of sugar.
The three tissues should give prints of about the same tonal range when printing with an identical negative and method and strength of sensitizer. #1 will have the least relief, #3 the most. Penetration of UV light should be about the same percentage of total tissue thickness in all three cases, so exposure time should be approximately the same for all three prints.
The appearance of relief also depends heavily on image type, and macro- and micro-contrast, and on choice of final support.
Sandy
Can I ask why the sugar content is inceasing? Are you expressing this as a total amount because more glop is required to pour a thicker gel, or is sugar concentration related to pigment load rather than gelatin load as I believed?
Bruce
Quote:
Originally Posted by sanking
The sugar content is increased with tissue thickness to allow same water penetration so that soak times will be more or less the same with thinner and thicker tissues. It has nothing to do with pigment loading.Quote:
Originally Posted by brucep
Sugar content may also need to be adjusted for RH of working conditions, but that is another consideration.
Sandy
Thanks, another useful fact to add to my notes.
Quote:
Originally Posted by sanking
My first carbon prints had no relief, but I could see it on the wet print, but not on the dry. That led me to increase the relief by 1) decreasing pigment to the minimum level required to still achieve a black on the print and 2) increase the contrast of my negatives -- clear micro shadows and almost blocked up highlights. I kept the sensitizer to 5ml of 8% dichromate for 100 sq inches of film (that 5ml is diluted 1:3 with acetone immediately before use).
I like using a stronger sensitizer and matching that with the high contrast on my negatives. Using food-grade gelatin, I get great highlights that do not wash off and seem to record those high values well.
Thicker tissues handle a little different than thin tissues, but other than that, I do not believe that tissue thickness has much to do with raised relief. As long as the tissue is thick enough so that one does not expose all the way to the base everything is cool. Pigment and sentisitizer concentrations and the qualities of one's negative will primarily determine relief. Whoops -- and final support type and surface qualities, too.