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  1. #11

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    Thanks for the comments, Katherine. They are helpfull for me too when I shall pick up my efforts in gum printing again.

    Greetings,
    G

  2. #12

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    hi,
    unfortunately i wasn't able to do more tests today, because it has been pouring all day. hopefully tomorrow will be more lucky...

    but i thought of another possible source of error. since i don't have a proper register, i sandwiched the paper and the negative between two pieces of plexiglass (about 5mm thick) and fixated it with screw clamps.
    i have just read that normal glass is a pretty good uv-filter and i read in another thread that plexiglass is an even better one (or not... both opinions were present in that thread).
    i could use normal glass (about 3mm thick, from a cheap picture frame) instead of the plexi.
    or should i completely avoid putting the negative and paper under any kind of glass? in this case, i'd have to build something...
    Last edited by phritz phantom; 08-29-2007 at 01:21 PM. Click to view previous post history.

  3. #13

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    finally an image!


    i got an old sunlamp, which was made in the 70ies or so, and it worked fine. exposure of 5 minutes, negative and paper under a sheet of glass, the lamp was about 60cm above the negative.
    how does that look for a first try?

    so, if i wanted to put a second layer of gum on it? how do i get the negative in exactely the same position as before? is there some kind of trick?
    and is it necessary to clean the negative after exposure? since it was in direct contact with the dichromate-emulsion. i don't think my inkjet negatives can be washed.

  4. #14
    smieglitz's Avatar
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    Quote Originally Posted by phritz phantom View Post
    ...i can only say that's an orange liquid (with a little bit residue on the bottom) and they recommend mixing it 1+1 with the gum solution...
    You also mention coating under dim light. The gum emulsion actually isn't very sensitive, especially when wet, so coating under average incandescent or fluorescent light conditions should be fine. Just be sure to dry it in dim light or the dark. If the correct viscosity, the emulsion should start to set while you are smoothing the coat. You will feel it start to get tacky and at that point, you should stop blending and either set it aside to dry or force dry it with a hair dryer set to cool (no heat). The emulsion should never be wet or thin enough to come off on your negative.

    You may wish to continue your discussion on the hybridphoto.com website for tips on the negative making and registration for additional layers.

    Joe
    Last edited by David A. Goldfarb; 09-04-2007 at 04:08 PM. Click to view previous post history. Reason: clarity; DG--poster request

  5. #15

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    Sorry, I missed some of these posts when they came in, so I'm a little behind.

    Thanks for posting your first image, pp; that must have been quite a thrill to see it come up at last.

    I don't know that it makes sense to talk about stain or overexposure with regard to this image, just because there's some tone in the highlights. This would be a concern only if you intended all the lightest parts of the image to be paper white, which would make it a rather contrasty image in spite of the somewhat weak nature of Payne's grey.

    It's interesting; five or ten years ago everyone was printing their test images to have some white in them, as a way of showing off the fact that there was no pigment stain in their gum prints; now I gather many people feel that there should be some tone even in the lightest areas. Whatever floats your boat, as they say here in the USA. But it wouldn't be for me to say that because there's some tone in your highlights, that automatically means there's something that needs fixing. If you said you meant the lightest areas to be white, and they didn't turn white, then we could go on to talk about stain or overexposure being the cause of the tone where there should be paper white.

    Katharine

  6. #16

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    Quote Originally Posted by phritz phantom View Post
    so, if i wanted to put a second layer of gum on it? how do i get the negative in exactely the same position as before? is there some kind of trick?
    and is it necessary to clean the negative after exposure? since it was in direct contact with the dichromate-emulsion. i don't think my inkjet negatives can be washed.
    When using a film negative, I just line up the negative with the image on the paper before coating subsequent coats (sometimes, as I've said before, my coating is so opaque that it's impossible to aline the negative after coating) and mark around the corners with pencil. Then after coating and drying, I simply fit the corners of the negative into the corner marks. When using paper negatives, I just mark around the corners of the negative before the first exposure, and keep fitting the negative into the same corner marks each time. It's not as precise as aligning the negative with the image, as you can do with film negatives, but it works surprisingly well.

    The coating should be dry enough before you expose that it shouldn't stick to the negative or get any emulsion on it; if you do, you're probably not drying the coating long enough.
    Katharine
    Last edited by Katharine Thayer; 09-04-2007 at 11:24 AM. Click to view previous post history.

  7. #17

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    Quote Originally Posted by phritz phantom View Post
    i really can't say anything about the sensitizer. also nothing on the fotospeed hp: no datasheet etc. i can only say that's an orange liquid (with a little bit residue on the bottom) and they recommend mixing it 1+1 with the gum solution. and yes, everything was pre-mixed.
    Joe is right; if you've got crystals settling out, then it's a saturated solution, and my surmise that maybe they diluted it is no doubt in error. But then I would question the 24 minutes in direct sun recommendation; that would be hugely overexposed even with potassium dichromate, as I said before.

    I've always used a 1:1 mix, and it works quite well for me. But you'd need to decide for yourself which is the best mix or mixes for you (depending on the goal of the particular layer).
    kt

  8. #18

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    Below I've run a quick test to show how an actual gum coating using quinacridone gold pigment looks when the recommendation to reduce dichromate as a proportion of coating mix is followed. I didn't calibrate the beginning exposure exactly for today's humidity, so it may not be perfect, but the absolute number of steps printed under any condition isn't relevant for this demonstration; what's relevant is the relative number of steps printed under the various conditions. (And try to overlook the streaks of blue; that's left over from that experiment with Prussian blue I did for a different thread last week. No matter that I cleaned up carefully afterward, there are still grains of blue pigment here and there to get onto things, which is why I don't work with powdered pigment as a rule).

    On top is a mix containing 1:1 gum/pigment: saturated ammonium dichromate, exposed for 3 minutes. In the middle is a mix containing 2:1 gum/pigment: saturated ammonium dichromate, exposed for 3 minutes. It should be apparent that, though there's no dichromate stain in paper white areas of either strip, the second one printed significantly fewer steps. But that's more a function of not properly adjusting the exposure time to the decrease in dichromate; when the exposure time was doubled in the third strip to compensate for the reduction in dichromate, then the number of steps printed was similar to the number of steps printed with a 1:1 mix. Note that there is neither pigment stain, nor dichromate stain, with either the 1:1 mix, or the 2:1 mix.

    Katharine
    Attached Thumbnails Attached Thumbnails Qgolddichromate.jpg  
    Last edited by Katharine Thayer; 09-04-2007 at 05:21 PM. Click to view previous post history. Reason: remove references to test that was mislabeled

  9. #19
    smieglitz's Avatar
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    Quote Originally Posted by Katharine Thayer View Post
    I'm sorry; I must respectfully disagree with the interpretation of the above-posted comparison.

    ... this is purely an illustration of dichromate stain, though it was seemingly offered here in support of a recommended solution to the perceived problem of pigment stain in the image.

    To take the comparison, in its original description, at face value and conclude that dichromate stain can be avoided by reducing the proportion of dichromate and increasing the proportion of gum in the mix...
    Katharine
    My bad. I did mix up the color test with the dichromate stain test scans. Sorry.

    However, I never inferred anything about dichromate stain in my original response and I'll stick to my suggestion that too much dichromate solution may thin the emulsion (because of the water content, not the total dichromate concentration) to the point that a specific pigment may be able to stain the paper (especially one given inadequate sizing or hardening) since it takes longer to set and the emulsion has a better chance then to soak into the paper rather than setting on the surface.

    I'll remove the example to avoid further confusion. Sorry.

    Joe

  10. #20

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    Quote Originally Posted by smieglitz View Post
    I'll remove the example to avoid further confusion. Sorry.

    Joe
    Okay, since you're removing the example, I edited my post (while I was still in the editing time window) so that it no longer refers to the example. No problem.
    kt

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