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Thread: Gum Bichromate

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    vintagepics's Avatar
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    Gum Bichromate

    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
    Rick Lanning
    Retired Crime Scene Photog.

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    artonpaper's Avatar
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    Three negs, RGB, then printed in CMY pigment.

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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.

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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.

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    vintagepics's Avatar
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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.
    Rick Lanning
    Retired Crime Scene Photog.

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    Mainecoonmaniac's Avatar
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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.

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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.

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    TheFlyingCamera's Avatar
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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.

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    vintagepics's Avatar
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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.
    Rick Lanning
    Retired Crime Scene Photog.

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    vintagepics's Avatar
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    Quote Originally Posted by TheFlyingCamera View Post
    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.
    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?
    Rick Lanning
    Retired Crime Scene Photog.

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