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  1. #1

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    Multilayer gum printing - adhesion

    I'm trying to figure out multi-layered gum printing, and the problem I'm having is that the second layer doesn't adhere. I may have not had enough dichromate in the sensitizer for my second layer (I mix very small amounts at a time (0.3 grams of potassium dichromate in 3-4ml water), and my scale has an error of +/-0.1 grams), but I wanted to see if there were other possible problems to consider.

    WHen I printed my second layer it started to develop okay, but then lifted away from all the exposed areas in solid clumps... so it hardened alright (or at least, to some extent), but broke up and didn't adhere.

    I do a sodium metabisulfite bath to clear dichromate stain; could that be impacting things if I didn't rinse enough? I'm not really sure what to consider here.

    I hope I don't have to size, but from what I understand sizing is about keeping pigment from adhering too much / staining, so I don't think that's what's going on here.
    The universe is a haunted house. -Coil
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  2. #2

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    Walter, what are you printing on? In my experience/observation this is a problem that tends to arise when printing on hard surfaces (plastic, metal, or glass, for example) that have little tooth, or when a too-thick or too-heavy size is used on paper so that it fills up the tooth in the paper and doesn't leave enough for the gum to hang onto. It sounds from your comments like you're not sizing, so the second possibility shouldn't apply, and if you're using paper, the first shouldn't apply. Varying amounts of dichromate would affect the speed of the gum layer but if the gum is coming off in flakes rather than washing off as a liquid (meaning the layer isn't sufficiently exposed) then I don't think it's the dichromate that's at fault.

    Another question: how heavy is your pigment mix? If too heavily pigmented, it can chunk off like that, but if it's that heavily pigmented, you would have trouble brushing it on the paper as well.

    Metabisulfite should not be an issue here, at all.

    Hope any of that is useful,
    Katharine

  3. #3

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    I'm printing on Fabriano artistico hot pressed; no extra sizing added.

    Interesting you say that too much pigment can do that; I doubled up the pigment for the second layer thinking I could avoid colouring the highlights by having more pigment but a shorter exposure (was aiming for higher contrast). Also it brushed on with a bit of difficulty and I couldn't get a smooth coating, it seemed too wet / runny. (This was also a different watercolour that I noticed had both gum arabic & dextrin as the base, instead of just gum arabic, so maybe that's an additional problem).

    The first layer was a very small amount of pigment and a long exposure (to try to get the highlights filled in without adding much density to the dark areas; low contrast)... there was quite a bit of hardened gum on the paper after this (so you could really see the texture of it while it was wet; pretty serious relief). I had this "brilliant" idea to try to do something similar to split grade printing on multigrade silver paper (a low contrast exposure for the highlights followed by a high contrast exposure to fill in the shadows).

    Instead of doing these radical pigment concentration things maybe I should try just using a lighter pigment (like transparent yellow) for the highlight layer, then a dark pigment for the shadows?

    BTW, I have referred to your site quite a bit while learning this process; you've done some really nice stuff. Thanks for offering your suggestions.
    Last edited by walter23; 02-27-2010 at 12:29 AM. Click to view previous post history.
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  4. #4

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    Hmm, I don't think we're talking about the same thing with the pigment; wet/runny doesn't describe the kind of heavily pigmented mix I'm talking about. I was talking about a mix that's so heavily pigmented it's like tar, and the difficulty I was referring to would be akin to trying to spread tar on paper with a brush. If a mix is wet and runny, I would say it's not heavily pigmented, by definition. Do you use extra water in your mix, or just the water in the dichromate solution? BTW, I'm not sure I see the reason for mixing such tiny amounts of dichromate; that seems like a lot of trouble to me.

    FYI: the same issue has been just recently been brought up on the alt-photo mailing list, someone having the same problem of third and later gum layers not adhering, same paper (Fabriano Artistico Extra-White) unsized.

    I don't use that paper, don't like it, but when I did try ten sheets of it just to see what all the hoo-ha was about, I found it a very absorbent paper, very easy to coat (which may be why so many people like it) which disqualifies it from the category of hard/slick/nonabsorbent materials that I was referring to in my earlier post, that can sometimes have difficulty hanging onto subsequent layers.

    Your thinking is good with the "split tone" idea; that's how generations of gum printers have printed both well-gradated highlights and dark shadows. Sorry it didn't work in this case. But there should be no problem with your method; I've done this routinely.

    I'm afraid I don't have any good answers, since the usual answers to this question don't seem to apply. Just grasping at straws, I'd say try a longer exposure for the second coat and see if that helps. Good luck,
    Katharine

  5. #5

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    Thanks Katharine; appreciate the help.

    For now I'll assume my first layer is okay and just try to sort out the second layer issue. I probably just made a bad batch of gum / sensitizer, it didn't seem to brush on right, and even a test print with just one layer of that batch didn't seem right to me (took a much longer exposure than normal).

    Should find a brown bottle and mix up a bigger batch of sensitizer to keep it consistent and make proportions easier to control. Does the dissolved dichromate solution last any reasonable length of time?
    The universe is a haunted house. -Coil
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  6. #6
    DarkroomDan's Avatar
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    Katherine didn't toot her own horn. Click on the URL at the bottom of her reply and it will take you to her website where you will find a wealth of information on gum printing.

    Dan
    Daniel Williams
    Enumclaw WA USA

  7. #7

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    Yeah, I have really enjoyed looking at her work and information... thanks for the reminder, lots of good information there.
    The universe is a haunted house. -Coil
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  8. #8

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    AFAIK, the dichromate solution should last a long time esp in a brown bottle. I made my first bottle in May of 2009 and it's still perfect. Find a 100ml bottle and mix it up all at once. There's too much of a variable when mixing tiny amounts for one-time usage.

  9. #9

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    The easiest thing to do is just mix up a saturated dichromate solution. Keep adding water until no more will dissolve, and you have a saturated solution. You can keep this in a big amber bottle and keep adding water until the dichromate will eventually all dissolve. At that point, add more dichromate until it's saturated again. This way your mix will always be consistent. I think it will last a very long time.
    Just make sure you don't shake the bottle before measuring it out for your print, or else you will get dichromate crystals in your mix.
    Steve
    www.scdowellphoto.com

  10. #10

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    Quote Originally Posted by sdivot View Post
    The easiest thing to do is just mix up a saturated dichromate solution. Keep adding water until no more will dissolve, and you have a saturated solution. You can keep this in a big amber bottle and keep adding water until the dichromate will eventually all dissolve. At that point, add more dichromate until it's saturated again. This way your mix will always be consistent. I think it will last a very long time.
    Just make sure you don't shake the bottle before measuring it out for your print, or else you will get dichromate crystals in your mix.
    Steve
    www.scdowellphoto.com
    That's great advice and will definitely make things easier and more consistent.
    The universe is a haunted house. -Coil
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