For starters I would suggest that most discrepancies or differences you see in procedures, either between me and other carbon workers, and even just with myself, are due to the fact that there are multiple ways of working carbon and many of them are equally effecient. In other orders there are many ways to obtain the same end. Also, bear in mind that the materials themselves vary a lot and one set of tissue or final support may require working procedures that are quite different from another. And the materials, especially tissue, changes with age.
But to the specifics.
“after reading your extended article found on the View Camera web site there are some procedural differences when compared to the instructions provided by Bostick & Sullivan.
First is the method of sensitizing the tissue. In your extended notes for tray sensitization you specify using only water for the dichromate solution. The B&S instructions specify acetone or isopropyl alcohol to be used for 50% of the solution volume. In contrast you recommend using a spirit sensitizer for brush sensitizing. Personally I would rather not use a spirit based method of sensitization.”
In my opinion tray sensitizing gives more consistent results than spirit sensitizing. I use both methods but for critical work I always tray sensitize using just a plain dichromate solution. Dick has developed his own method of sensitizing and I am sure it works well but I don’t use it quite simply because there is no doubt in my mind but that tray sensitizing is the better procedure.
“Second, your article has much more specific details about what dilution of dichromate to use for various negative DRs. Specifically you wrote, 'In working with the B&S carbon tissues it will be found that the practical effective range of a potassium dichromate sensitizer varies from a low of about 1% up to a high of around 3%.' However in your curve illustrations you show plots for dichromate solutions that range from .25% to 2%. I'm not sure what practical conclusions to make of that. In other words can .25% really be used with the B&S tissue or is 1% the bottom limit? Or are you simply making the point that a .25% dichromate dilution will produce an incredibly slow tissue? The B&S instructions specify a .5% dilution for a 'silver style' negative. Whatever the real limitation may be I'll measure the DR of my negative to see if I can practically make a decent print with it. Unfortunately it is a pyro (PMK) stained negative and I don't have a UV densitometer to measure the effective DR.”
I consider 1 – 3 % dichromate solutions to be the practical limit. Speed drops off very rapidly below 1%, and above 3% the exposure scale of the tissue becomes longer than necessary. At 3% it is already close to log 3.0 and who prints with negatives of that density range? So the practical limits for me are determined by speed at 1% and ES at 3%. However, dilutions weaker than 1% do work and it is in theory possible to print a negative made for silver printing with a 1/4% or 1/2% solution.
“Third, it is interesting to note from your article that the ES of the printing process is determined by the combination of tissue/sensitizer. I can understand that, but isn't the final contrast of the print also influenced by the receiver paper (at least to a small degree).”
The exposure scale of the print does not vary very much with papers. But the look of carbon prints varies a lot according to the nature of the final support. Smooth papers give more sharpness and Dmax, while images on textured papers have less detail and the Dmax is lower. The differences can be very dramatic.
“Fourth, the B&S instructions suggest that the tissue and transfer paper be mated for about 10 minutes before development begins, you on the other hand specify 30 minutes. Perhaps you touched on this in the public ally published version in View Camera, unfortunately my copy isn't handy so I can't compare. What effect does the RH and ambient temperature have on the transfer?”
You may be able to get away with a ten minute mating of the tissue and support paper, but 30 minutes is safer in my experience. High RH and ambient temperature will result in a darker image. But it is complicated to work carbon at all when the temperature is over 75º F or the relative humidity is over 80%. In general the longer the tissue and support stay mated the more they will stick together, which will reduce the possibility of frilling during hot water development. But keeping the sandwich together for a very long time, say 1-2 hours, will result in a print that is visibly much darker than if the sandwich is kept togther only 30 minutes. This is caused by what we call the continuing effect.
“Fifth, its not clear to me from reading the B&S instructions and your extended article what is the proper length of time for presoaking the receiver paper.”
There is no one single proper time. Soak time has to be adapted to the specific paper and to the temperature of the soak water. If you keep the soak water at 65º F or below you can soak most papers all day and they will not absorb too much water. On the other hand, if the water is over 70º F the paper may absorb too much water with a soak of just a minute or two. As a general rule I recommend keeping the water at 65º F or lower. At this temperature a soak of two minutes is enough for fixed out photographic papers whereas a sized watercolor paper may need five minutes or so. The main problem is that if the paper absorbs too much water it will not stick well to the tissue and there will be a risk of frilling during development.
Hope this is useful.
Last edited by sanking; 09-02-2004 at 03:10 PM. Click to view previous post history.