Gum Bichromate

Discussion in 'Alternative Processes' started by vintagepics, Sep 21, 2011.

  1. vintagepics

    vintagepics Member

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    Im just now starting to research gum printing, and have a basic understanding. One of the problems I am having is finding information on color printing. I have seen basic explinations on several forums and posts but no information pertaining to my question. Im either reading over it, or just not getting it. When color printing, are you actually using a color negative, or are you making several negatives of the same image in CMYK or RGB? Are you then using the one color negative to make several exposure in the different colors, or are you using the several different colored negatives on the different pigments? I hope my question is not too confusing. Thanks

    Rick
     
  2. artonpaper

    artonpaper Member

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    Three negs, RGB, then printed in CMY pigment.
     
  3. TheFlyingCamera

    TheFlyingCamera Membership Council Council

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    If you are aiming for "natural" color rendition, you are making what amounts to CMYK separations and printing in multiple layers. You'll need to include some kind of registration system to avoid out-of-register layers and very soft/low resolution prints. If you go for a CMYK approach, you'd have 4 b/w negatives you'd have to print. You could probably make it work with just an RGB separation, but there'd be a chance your shadows would be literally muddy instead of black. I'd think you'd print the black layer first, then the color layers on top, but I wouldn't swear to that, as I don't try to print "natural" color when working in gum.
     
  4. BrianShaw

    BrianShaw Member

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    There are many good books available that discuss alternative printing, including gum bichromate. Many of these books are out-of-print but can be found via the various old book sites. New ones seem to constantly replace those that go out of print. The gum bi sections seem to be stable and not affected by too much new technology or technique.

    Not to discuourage you, but I've found gum bi to be sufficiently challenging that even monochrome has a significant learning curve. I'd suggest mastering monochrome gum bi first.
     
  5. vintagepics

    vintagepics Member

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    Thank you all very much. I have read that gum bi is so easy that a 4 year old could do it, but I don't have a 4 year old, so I know I will be challanged. I agree with you Brian, Ill try the mono first. Hopefully by then I can get some books together.
     
  6. Mainecoonmaniac

    Mainecoonmaniac Subscriber

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    I think RGB is for mixing colors with light, but CYMK is for mixing inks. An example are computer files are RGB, and printing presses have Cyan, Magenta, Yellow and Black or "K" which means keyline.
     
  7. GumPhoto

    GumPhoto Member

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    One of the nice things about gumprinting is that there are no rules. For many years I used CMYK separations, but lately I have found that it is easier to just flip the RGB files, using R for Cyan, G for Magenta and B for yellow. If you feel it necessary, you can print an additional neg for the black by simply using only the K channel of a CMYK separation. You can also pound in some shadows by adding a layer of black using a reduced exposure with your R negative (or C if you are using CMYK). This probably sounds confusing, but it becomes very intuitive with a little experience.

    While Brian's suggestion has merit, I found it did not work for me, as my initial attempts at monochrome were quite dismal. What you might want to try is an approach I have used in workshops: print separation negs, but then use them to print three layers of the same monochrome color. When you start getting some positive results, then print using a very muted palette, say gray for cyan, burnt umber for magenta and raw umber for yellow.
     
  8. TheFlyingCamera

    TheFlyingCamera Membership Council Council

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    Vintage-

    A good book on gum bichromate printing (the one I learned from) is the Sarah Van Keuren book "A non-silver manual", which is now available for download from alternativephotography.com. She does cover how to do "natural" color gum printing as well as monochrome and interpretive color. If you'd like to see it, I have a hard copy of my own. Will you be attending the alt process demo days at Photoworks as part of FotoWeek DC this November? The guy who taught me how to gum print will be showing work and teaching that week as well.
     
  9. vintagepics

    vintagepics Member

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    I hope I don't sound like an idiot here, but I have never heard of Fotoweek DC. I just googled it and put it on the calender. As long as w**K does not get in the way, Ill be there on one of those days.
     
  10. vintagepics

    vintagepics Member

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    So I assume I digitize the print i want to make. In Photoshop i convert the color image to a color negative. Seperate them in channels to CMYK, then print each channel as a B&W transparency. Then through whatever registration system I come up with, print each layer, probably starting with black (K). At printing time do I then use the C layer to print the blue, M red, and Y yellow?
     
  11. GumPhoto

    GumPhoto Member

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    Here's how I would start: Convert the image to CMYK. Invert the image. Split channels, print and label the negatives. Start with the Cyan, then Magenta then Yellow then Black. Unless you have a totally mechanized approach, your development will require some observation to determine when a particular layer has cleared. This would be difficult to do if black were your first layer. Many gumprinters never use black (and the forums would get heated at times regarding this). I DO use black, but I always put in on last, because this allows me more control.
     
  12. BrianShaw

    BrianShaw Member

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    I'm in complete agreement, with one exception. Why not do this with a regular B&W neg to get an understanding of the various gum printing variables and registration? Why hassle with separation negs until those basics are well understood?
     
  13. David Hatton

    David Hatton Member

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    Thats correct. However if you use rgb instead of cmyk, the you will use the complementary colour ie
    R = Cyan
    G= Magenta
    B= Yellow
     
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  15. R Shaffer

    R Shaffer Member

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    +1

    Start making gum prints and get a feel for the process.
     
  16. vintagepics

    vintagepics Member

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    I agree with all. Here is what I did just to get my feet wet. I ordered two kits from Adorama, one for doing black gums, and one for doing color gums. It says each kit will do fifty 8x10 gums. I will start with the black and work my way into the color once I get the understanding. I like jumping the gun a bit on the learning curve. Have any of you had any experience with these kits?

    Rick
     
  17. GumPhoto

    GumPhoto Member

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    No reason not to. It seemed like the OP wanted to do full-color and I thought starting off with separation negs could be the faster approach. AND the subtle differences in the multiple monochrome layering does provide a nice end result. Taking an approach like this encourages the print to be "built", which is the same tactic taken with full-color gums. But using one negative is certainly easier. Registration will still be an issue.
     
  18. TheFlyingCamera

    TheFlyingCamera Membership Council Council

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    I've never used the Adorama kits. I didn't even know they offered one. I've been buying my materials for gum from Bostick & Sullivan for the most part, except my pigments and occasionally my paper from Utrecht.
     
  19. BrianShaw

    BrianShaw Member

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    Sometimes that can be a great personality trait! Good luck with your new venture!

    What are you using for a light source and negative registration method?
     
  20. artonpaper

    artonpaper Member

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    This is true and photoshop does have a CMYK work space. But if one separates the channels in RGB then inverts those to negatives, those negatives can be printed in their complimentary colors, Red to cyan, green to magenta, and blue to yellow. It's also true that without a K or black negative, the shadows may be muddy. A K negative is most easily obtained in CMYK.

    In addition, I think it very good advice to start with monochrome. I don't think gum is for four-year-olds. It is necessary to learn the technique and establish a good exposure range, and pigment to gum mixes.
     
  21. vintagepics

    vintagepics Member

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    Full color is my goal, especially the color stylings of the old 1940s post cards, but I don't mind starting at the bottom. B&W is still a true love.
     
  22. vintagepics

    vintagepics Member

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    I was going to be using sun for my light. Its worked well with my salt prints and calotypes. As far as a registration system, I have not given that much thought yet. Im open for any suggestons.
     
  23. GumPhoto

    GumPhoto Member

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    If negative cost is a factor (if you are using Pictorico, for instance) you can cheat on the "K" negative by using whatever neg you use for Cyan and substituting black pigment. Use 50-60% of your usual exposure, and the black will only sit in the shadow areas and not affect the "real" cyan in the rest of the print.
     
  24. holmburgers

    holmburgers Member

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    If I may wax poetically on color theory for a moment...

    Our eye's have rods & cones, and of the cones there are 3 types; sensitive to red, green or blue. These sensitivities cover (or rather constitute) the visual spectrum of light. Nature's infinite & continuous spectrum of light is reduced to 3 discreet & finite channels in our eye. This is color photography's goal as well.

    So how do we transmute a visual image of nature onto a piece of paper?

    First we must replicate the sensitivities of the eye with our recording media, film. Panchromatic sensitivity was the longest held stumbling block to color photography. Color separation filters mimic the sensitivities of our 3 cones, and the 3 layers of a color film strive to do the same, as does a digital sensor.

    Once we have separate records of the red, green & blue light in a scene, we have to assemble these in a way that will reconstitute the color sensation of the original scene. We will always take separations from the red, green and blue light present in the scene, but to make a print on paper (or a slide) we can't use pigments of these colors since the combination of any two primaries would result in black. This sounds contrary, but red absorbs blue & green, and blue absorbs green & red, and so on. If you overlay any 2, the result is complete absorption.

    We have to use the minus colors (the color complements, secondary primaries, primaries in the sense that we all learned in grade school). Cyan is minus-red, magenta is minus-green, and yellow is minus-blue.

    Cyan freely transmits green & blue (in theory at least) and absorbs red as the white viewing light hits the print and is reflected back from the white surface of the paper. In this way only the red light (present in the white viewing light) is modulated by that layer. That's why the red record becomes cyan, the blue yellow and the green magenta.

    CMY allows us to affect the absorption of only 1 of the color sensations at a time. The combinations possible therein can recreate all color sensations that we are capable of experiencing (again, in theory, and in practice it's pretty darn close).
     
  25. GumPhoto

    GumPhoto Member

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    When using paper as a substrate, the easiest method to register visually through the print over a light table. Even with preshrinking there will be some change in the paper (although at 8x10, not very extreme) and this approach will allow for you to select the place where you want the maximum sharpness.
     
  26. vintagepics

    vintagepics Member

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    I have read several different methods for sizing the paper, but have any of you ever used albuman for this?