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  1. #1

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    Carbon highlights "eaten out"

    Hi,
    I'm still on my Carbon learning curve and I'm starting to get some predictable results.
    One thing I can't get over, though, is that all my highlights (zone VIII and IX approx.) look like "eaten out", i.e. beyond zone VIII the gelatin/pigmant is completely gone.

    Highlights look like large white holes. The other gradations are perfectly smooth.

    I'm using the pre-fabricated tissue from B&S, spirit sensitized with 2%-4% potassium dichromate (12ml for an 8x11 sheet). As a support, I'm using Fabriano Artistico paper with an 8% gelatin sizing (20ml with 4 drops of formalin for a 11x14" sheet, hotdog-rolled). Never had major detachment issues.
    I develop my print by turning it face down after de-mating and let it float without moving in 95-105F (35-40C) for 15-20 minutes.

    What could I be doing wrong?

    Thanks
    gm
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  2. #2
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    My guess is that between the low amount of dichromate in the tissue and the density of your highlights, the tissue just is not receiving enough exposure in your highlights to harden any of the gelatin -- thus no image. I would just try a 8% solution of sensitizer and see what happens -- it will lower the over-all contrast and hopefully keep your highlights without flattening the other values.

    It is difficult to compare results with different tissues, etc. My home-made tissue has a much lower contrast 'grade' than the B&S tissue, as I use a lot less pigment. My negatives are also have a very high DR...never actually measured it, but it they are probably well over 2.2. For an 8x10 (9x11 tissue) I am spirit sensitizing with 5ml of 8% Ammonium dichromate (diluted with 15ml of acetone -- so that equates to 20 ml of a 2% solution).

    Good luck!

    Vaughn
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

  3. #3

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    Vaughn, thanks for your reply.
    I tried concentrations and exposures at several different ranges, from 2% to 6% (I use twice as much as solution as you, so my 2% is your 4% in terms of dichromate per square inch).
    Exposing longer would give me a smooth tonal range in the highlights, but the image is too dark. When my highlights approach the desired value (zone VIII), there is a sudden drop in density. If I were to draw a curve, you would see a steep drop in the lower densities instead of the typical carbon toe.

    Where I would expect to see zone VIII and IX grays I see paper white. So I doubt it's the highlights being underexposed.

    It looks like the gelatin gets particularly fragile when it's thinner and falls off, even if I use no agitation in development. I'll post a scan of my test strip when I have access to it.

    I also wondered if I was using too little solution and missing spots during my brushing. I prefer 12ml for a 8x10 so I get a more uniform coating, but if you say you use half of the amount of liquid, maybe that is not the problem.

    Thanks
    gm
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  4. #4
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    Actually, I use 20ml of liquid for an 8x10. I just base my sensitizing on the strength and amount of stock solution (5ml of 8%) that I then dilute 1:3 with acetone (5ml + 15ml). If I was using alcohol instead of acetone, I might use it 1:2 (for a total amount of 15ml). Acetone evaporates so fast that I like using a little more than I did when using alcohol. But in the end, I am still delivering 0.4 grams of dichromate per sq inch (a nice mix of units there. LOL!)

    I have seen such highlights as yours in workshops I have given. There has been two causes that we were able to correct. 1) digital files that clipped the highlights. or 2) too low of a concentration of sensitizer (not enough dichromate) used to compensate for negatives that had too low of a contrast range.

    In your case, it just sounds like your negatives have too much contrast for the B&S tissue, but without seeing the negatives, I am not 100% sure of this.
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

  5. #5

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    That makes sense. So I'm indeed using much less overall liquid, and actually I can see some irregularities on the surface.

    From my previous experience with other dichromate processes, where I brush sensitized clear gelatin, if I hesitated just a fraction of second while brushing, the first brush strokes would show up clearly as more intense orange patches. You can't notice this on the pigmented carbon tissue, but dry gelatin is very thirsty.

    I might try pre-brushing some distilled water (with some acetone, but not too much or it will dry out too fast) in order to get the surface slick and have the dichromate spread more evenly.

    I can also try to size my support in two 4% gelatin coats instead of one 8% coat. The thicker gelatin might create a rough surface that compromises the adhesion of the support.

    I'm not quite following you on the dichromate amounts. 5ml of 8% concentrate makes 0.4 g of dichromate for your 8x10" sheet, which makes 0.005 g/sq. in - right? I'm using 12ml of 2% solution on a 8x11", which makes 0.0027 g/sq. in, so it has more contrast.

    I don't have a densitometer, but I can say my negative is quite thick but not too contrasty.

    Thanks for your advice, I'll let you know how it goes.
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  6. #6

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    Hi,

    I have had the same problem of loss of highlights and it can occur if the sizing on the paper is not hardened quite enough; I think of the problem as a 'micro frilling' issue where the very thin highlight gelatine does not quite stick well enough to the support. The sizing is hard enough to stop much of the frilling issues, but not quite strong enough to hold onto the highlights. Try painting on a 5% solution of formalin onto a sheet to harden it some more and see if the highlights change.

    I also have had the problem when the mating bath was too alkaline and the gelatine sizing on the paper gets a slightly 'slippy' feeling in the mating bath. A dash of citric acid solution (e.g. stop bath) can help in this case and I now slightly acidify the mating water routinely now as it always seems to have a positive benefit with image adhesion.

    Best regards,

    Evan

  7. #7
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    Quote Originally Posted by gattu marrudu View Post
    ...I'm not quite following you on the dichromate amounts. 5ml of 8% concentrate makes 0.4 g of dichromate for your 8x10" sheet, which makes 0.005 g/sq. in - right? I'm using 12ml of 2% solution on a 8x11", which makes 0.0027 g/sq. in, so it has more contrast.

    I don't have a densitometer, but I can say my negative is quite thick but not too contrasty.

    Thanks for your advice, I'll let you know how it goes.
    Sorry, I wrote a response right away, but must have forgotten to click on "Submit reply"!

    And sorry for the math error. I meant that a tissue for an 8x10 negative gets a total of .4 grams of Ammonium dichromate. The actual tissue size is 9x11, close enough to call it 100 sq inches, so I use 0.004 grams per sq inch. The amount you use per sq inch is what I standardize on for my workshops, and I consider 0.0005 per sq inch to be about the lower limit.

    But the B&S tissue has a much higher inherent contrast than my tissue I use and that I make for my workshops.

    I use fixed out photo paper for my own work and for the workshops. So I have not witnessed the mirco-frilling...but will keep an eye out for it in the future.

    Good luck in refining your process!

    Vaughn
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

  8. #8

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    Quote Originally Posted by banana_legs View Post
    Hi,

    I have had the same problem of loss of highlights and it can occur if the sizing on the paper is not hardened quite enough; I think of the problem as a 'micro frilling' issue where the very thin highlight gelatine does not quite stick well enough to the support. The sizing is hard enough to stop much of the frilling issues, but not quite strong enough to hold onto the highlights. Try painting on a 5% solution of formalin onto a sheet to harden it some more and see if the highlights change.

    I also have had the problem when the mating bath was too alkaline and the gelatine sizing on the paper gets a slightly 'slippy' feeling in the mating bath. A dash of citric acid solution (e.g. stop bath) can help in this case and I now slightly acidify the mating water routinely now as it always seems to have a positive benefit with image adhesion.

    Best regards,

    Evan
    I have tried with acidifying the mating bath, but the problem still persists.
    As for the substrate hardness, that's interesting - I just gave my paper a further formaldehyde coating. In this case, is it advisable to rinse the paper after it has hardened, so the formaldehyde doesn't seep into the carbon tissue during mating and harden it?

    Attached is a detail of a print where the highlights appear as a white pool - yes, the negative is very grainy, but I would still expect a smoother gradation from light grey to paper white.

    Thanks
    gm
    Attached Thumbnails Attached Thumbnails mlg-carbon-1-detail.jpg  
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  9. #9

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    Hi,

    Yes I often give the paper an extra wash a few days after the formaldehyde step just to be safe. I have used paper by accident that had been coated with formaldehyde 24 hours earlier without washing it and it was ok; the mating bath will help was out residual formaldehyde but I did pull the tissue after 20 minutes just in case.

    Best regards,

    Evan

  10. #10
    CMB
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    It is painful to read of your quest for highlight detail in con-tone carbon printing. While many will come forward with advice the sad truth is that carbon prints have a well-documented problem with the loss of highlights (see the 11-17-11 APUG Post: Highlight Loss in Carbon Printing) This can easily be seen when printing a step wedge, but most carbon enthusiasts print "pictures" and are satisfied with the results of their efforts.

    Charles

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