Unit to print paper negs. on carbon tissue

[blindpig]

My intention is to test with a pre-made grey scale 8X10 or so in size.it would have approximately 9 steps from black to white each about 1/2 or twice the exposure of the next step,these steps would be horizontal on the paper.Then put vertical black borders an inch or so apart and expose the tissue to each vertical 1 inch wide strip at a increasingly longer exposures. Hopefully resulting in an approximate exposure time.My thinking is the black dividing borders would keep the grossly under exposed strips from lifting the adjacent strips with more exposure when developing and transfering.May have to try this more than once I expect with longer exposures but should eventually arrive at a desirable exposure(if this gadget works).Still waiting for the tissue and all to arrive,wish me luck...
Don

[blindpig]

Just now received my package from Bostick and Sullivan and am getting pretty excited.Have to make the step scale mentioned in last post and off to testing!
Am hoping that using their professionally made tissue and clearing some print paper for the receiver sheet will eliminate some variables and afford a good result without using up all the materials. I have 12 SQ feet of tissue, 30 Gr. of Potassium Dichromate and 100 Gr.Sodium Metabisulfite,enough for a start don't ya think?
Don

[earlj]

Good luck, Don. PM me if you get into trouble with the sensitization, development, and transfer of the carbon tissue. Soon we will have you ordering gelatin to make your own glop . . . . .

[blindpig]

Well. test#1 TOTAL FAIL! can't say I wasn't expecting something like this.My 15" lens has a coating and evidently it's very good'cause after stepping exposures from 5 minutes to 40 minutes there wasn't even the slightest evidence of density on the receiver sheet and not showing on the tissue either.The only next likely lens I have is a uncoated 10" projection lens I just found in my stash soooo only a slight delay for adapting this lens and on to test#2.
Disappointed but undaunted,more to come.
Don

[blindpig]

OK! test #2 FAIL! I adapted the 10" uncoated lens and tried second test. Thinking one of the problems could be my sensitizer mixture and/or temperatures(or lots of other things)I decided to try contact printing my mixtures etc.by darkening my shop and exposing an 20 step film negative step wedge in contact with the tissue in the copy board directly in front of the lights.The result is a 3 step carbon print with areas not covered yielding a dark gray not total black as hoped. The lights are two 400 watt metal halide about 12" from the copy board,exposed for 6 minutes.The sensitizer is a 3% solution of potassium dichromate,spirit coated on the tissue.
My best guess is the percentage of dichromate needs to be lower to increase contrast (or not) so guess that's next. Any and all suggestions will be appreciated.
Don

[blindpig]

OH! Guess I forgot to mention I'll be increasing the exposure a lot. May need more light like a couple of 1000 or 1500 watt halides,we'll see.

[earlj]

Don -
Have you used your exposure unit for another process? Can you print a cyanotype with it?
The carbon process has a very long scale - you should get more than half the steps of your 20 step wedge if everything is working right. It sounds like you are not getting enough exposure.
What is the temperature of the water for your mating bath? What is the temperature of your development bath? Was the tissue backing easy to peel?

[banana_legs]

Hi Don,

Yes decreasing the sensitiser concentration will increase the contrast, but it will also mean you need to increase the exposure to get the same base black. The rough guide I use (not precise by any means, but is usually close) is that halving the sensitiser concentration will need double the exposure to get the base black back, and will shorten the scale by 3 steps on a 21 step wedge (i.e. 3 half stop steps). Reducing the distance from the lamp to the print will reduce the exposure times quite quickly (it is a square law, so 1/2 the height will reduce time by 2 stops), but there is a risk of uneven illumination if you get too close.

As Earl says, it sounds like a much longer exposure (or similar with brighter lamps) with the 3% solution may be a better place to start to get a decent black, followed by a reasonable number of steps with tones. Increasing the sensitiser concentration will improve the black level for the same print time and also give you more tones. The other issue for losing density is when the image is difficult to wash with lots of bits of undissolved tissue remaining for a while after the peel; if that was the case, the print could have stayed too long in the developing water and resulted in a loss of pigment (the solution in that case is usually to soak the tissue longer in the mating to absorb more water into the gelatine before developing). My prints take between 5 to 10 minutes maximum to develop, with only a minimal amount of 'jiggling' in the water.

I did do some printing with very low concentrations of dichromate (down to 0.5%) and in front of a bank of UV tubes, some of the prints needed over an hour exposure.

Best regards,

Evan

[blindpig]

Earl,the temp of mating bath was 60 F and dev bath was 103 F, the tissue separated easily and I agree more exposure is necessary along with some physical changes to the equipment to aid the exposure.The development time was 5 minutes soak then peel and about 6 or 8 minutes more soaking with an occasional jiggle and the water draining from print was clear.
Evan,I'm going to move the lamps closer it will require some "creative"engineering but think some change is possible.Talked to my son last night and he is in the process of acquiring some Halide lamps being removed from a large commercial building and will check the possibility of some being 1000 or 1500 watts (luck may be with me).Presently am going to stay with 3% sensitizer solution and lengthen exposure time,may increase sensitizer percentage later to help shorten exposure time as well.
Thanks you guys for the help,please keep it coming.
Don

[blindpig]

Earl, sorry I didn't answer about other processes with this set up.No I haven't tried any other processes except shooting paper negatives in-camera which doesn't qualify as another process technically.Carbon printing and paper negatives are all I'm into right now and being conservative (read cheap) is about all I can afford to invest in financially and mentally so far.
Thanks again for the help,
Don