Carbon Transfer printing times

Discussion in 'Alternative Processes' started by SMBooth, Mar 8, 2015.

  1. SMBooth

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    What the general practice for determining CXfer printing and sensitising strength? Determine a black time by print though the film base then select sensitiser % by the max film density?
     
  2. Vaughn

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    The useful sensitizer strength runs generally from 1 to 10 percent. For beginning the process, I suggest using 4% as a starting point. I go for negatives with higher contrast, my glop has a minimum of pigment loading, and I work with an 8% sensitizer solution...and occasionally use 6% down to a rare 4%. The pigment type and load will have a great affect on all this, too. I use Grahams Watercolor -- Lampblack at 0.5 to 0.7 percent. (750mm water, 90 gr gelatine, 60 gr sugar, 4 to 5 ml pigment...makes about 850ml of glop). I would suggest using a little more pigment to begin with -- maybe 6 to 7 grams or equivilent.

    Once you have picked a pigment and pigment concentration, and sensitize the tissue, do a test to find when the film rebate's black matches the black of the print where there was no film over it. That is your minimum exposure time for those factors (pigment and senisitizer strengths).
     
  3. Andrew O'Neill

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    Yes. Use the minimum time to achieve maximum black. Sensitizer strength depends on your negative's density range. I use about 6% to 8% for my film negatives. 12g of lampblack water colour paint per litre of glop. I also use 90g gelatine per litre.
    Welcome to the world of carbon transfer printing!
     
  4. OP
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    Thanks, just getting back into this and want to start the right way not the hit and miss way like last time.
     
  5. andreios

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    Taking opportunity to clear one question - so for negatives with "normal" to "lower" contrast one should increase pigment load and (or or) lower the strength of senzitizer?
     
  6. RowanBloemhof

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    Well. You can choose either to change your pigment load or sensitizer strength to alter the contrast of the print. Yes lower percentage sensitizer increases contrast. So does increasing pigment load. Both come with a con. Higher pigment load decreases the height of gelatin layer applied to the final support, therefore "generally" decreasing the perception of relief. Decreasing sensitizer strentgth comes with a slight decrease in exposure speed. Also i seem to notice that its easier to create streaks on the tissue with your brush when using lower sensitizer strength. But that might due to my workflow and way of dilution.

    An obvious pro to changing contrast with sensitizer % is that you can do it on the go per print. IT would be quite a hassle to change pigment load per sheet of tissue
     
  7. andreios

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    Got it, thank you. :smile:
    Now just to get some TIME to actually do it... :sad:
     
  8. Vaughn

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    When I taught myself carbon printing, I kept the sensitizer strength constant (5ml of a 8% stock solution per 100 square inches of tissue), and worked with the pigment strength and negative contrast to get the prints I wanted. It was not until I started to give workshops and worked with negatives that were all over the map that I started to change the sensitizer strength. I feel that 4% to 5% is a nice starting point, as there is room to go up and down in concentration, if needed, without getting close to the workable min and max concentrations.

    With pigment concentration I eventually got to a point where less pigment would not yield a good black, and then I standardized my glop based on a little more pigment than that. Part of my goal was to have significant raised relief, which is accomplished through a low pigment content. So while one can increase the pigment concentration to increase the native contrast of the tissue, the cost will be reducing the amount of raised relief.

    I worked on my negatives to achieve what many people are doing now with inkjet negatives...create consistent negative quality (over-all density and the density range) to allow for easier tissue manufacturing. I try to produce tissue of the same native contrast while having the option to change the color sightly (warmer or cooler). I do get some variations in my negatives (I am not an exposing and developing machine), but generally I use the 8% sensitizing solution. I have a few negatives that I might try a 10% to 12% sensitizer solutions -- the contrast got away from me on a few negatives!

    I find that with very low sensitizer levels (around 1%), it can be difficult to maintain the detail in the highlights...the very high values tend to wash out.
     
  9. OP
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    OK Thanks for your help.
    I settled on 20ml / 1000 ml of Sumi ink from past experience and as a base point 4% PotD solution using 4ml per coat on a 8x10 sheet (i did two coats, 2ml PD & 2 ml Isoprop each, so in 8ml total).
    My black point came to 8min under BL tubes.
    Using a 21 step wedge i exposed for 8 min and got a range in steps from 1 down to 14 , even 15 but my coating was a bit uneven.
    Putting step 14 at a density of 2, does that now mean I need to make negative out to a max density of 2 (ish). Follow that theory if right if the test same will 2% and 6% that will give me a idea of % solution to use with various negatives.
    I should of done this testing first time around...
     
  10. Vaughn

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    If the coating remains uneven, you might try adding more alcohol (1:1.5 or 1:2). This will give you more time to brush it around the real estate.
     
  11. OP
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  12. Vaughn

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    My pleasure.

    I eventually switched from alcohol to acetone. I use it at 1:3 -- 5ml stock:15ml acetone...9x11 tissue for 8x10 neg, brushed on half at a time. Lots of fluid to work with, but evaporates much faster than alcohol.
     
  13. Andrew O'Neill

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    And acetone smells better!
     
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  15. Rick A

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    I don't like the smell of either, but switched to acetone and got better results.
     
  16. Vaughn

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    My Ammonium dichromate/alcohol mixture would turn dark before I could brush it on -- this was just after some changes in the way it was being supplied by the drug stores. One could not find 97% anymore -- only 92%, and who knows what else they put in it. That was the reason I switched to acetone. The smell, ease of use, and the results were what kept me using it.

    I ran high body temperatures regularily as a kid -- my mom would use rubbing alcohol on my back to try to bring my temperature down. The smell of rubbing alcohol does not bring back great memories!
     
  17. Rick A

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    The one thing I forgot about acetone vs alcohol, I can't measure acetone in my styrene beakers. It only took one time before I remembered why I shouldn't have done that.
     
  18. pschwart

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    Use whichever works best in your own workflow -- they will yield equivalent results when handled correctly. Isopropyl is actually a better choice if one brushes continuously and squeegees off the excess since acetone is much more volatile and can bind and cause streaking when you squeegee. The added volatility also means you have to take greater care when brushing acetone. There is a whole list of reasons why I don't like acetone -- chacun à son goût.
     
  19. Andrew O'Neill

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    Never had brushing issues with acetone. Yes, you have to work quickly. Foam brush works best, or foam roller. I never squeegee.
     
  20. pschwart

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    My point exactly -- materials have to be chosen for individual workflows. Should also mention that some foam rollers/brushes are dissolved by acetone. If you haven't encountered this yet, you are in for a
    treat :smile:
     
  21. Andrew O'Neill

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    Yes, I have heard of that! Hasn't happened to me, even with brushes from the dollar store! Fingers crossed!
     
  22. Vaughn

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    Yes, that happened to me! I find the plastic cans that 35mm film come in work nicely to hold up to 20ml...the amount for an 8x10 (9x11 tissue -- I use two film cans for an 11x14 negative). I tend to sensitize the tissues for a printing session all at one sitting, so I can measure out all the sensitizer/acetone mixes and cap them. I then coat each sheet, dry them and put them in a box -- and start printing. I use a paint brush -- about 1.5 inches. Purdy makes nice ones.

    But I am working on a new darkroom and I imagine my methods will have to change a little to adapt to the new space and conditions.
     
  23. OP
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    Vaughn, how much do you get between sensitising and exposure. I thought there was a relative short window between the two.
     
  24. Andrew O'Neill

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    For me, it's 3 hours when the RH is 60.
     
  25. OP
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    Thanks Andrew, I thought it was around that time but hoping for longer so could coat and store overnight.
     
  26. Vaughn

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    I will coat around 8 tissues for an evening's printing. Dry in about two hours, then I print for the next 8 to 10 hours. So I will have some sheets sensitized and dry for up to 8 hours before exposure.
     
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