U of S | Mailing List Archive | alt-photo-process-l | Re: new gums

Re: new gums

(SNIP) For the last couple of weeks I have been trying to be less technical about gum.
Speaking of being less technical, Malin Fabbri posted a gum article I wrote here:
which describes a "less technical" way of doing gum, digital negatives of course.  It is a lossy way of making diginegs which works good enough.
When I teach alt I teach the Precision Digital Negative System, but I start the semester with it and so by the time gum printing comes along they know the system well, though calibrating three different colors takes more time than calibrating a single coating process.  But it is impossible to teach this system in a 2 day workshop where I am also trying to teach tricolor gum, as you can imagine--the latter being more than a day in itself. And then try doing that with non-Photoshop users.
Thus I was trying to figure out an easy way to get a good enough tonal range in a gum print with trying to match the usual 4-6 stop range of gum--how to get highlights to print in before the shadows block up. How to make an adequate neg that was close enough to just inverting and printing it out.
The initial idea didn't pop into my head like Newton, but springboarded off of Heinrich Boegh (sp) who in his solarplate book used a curve that merely brought the top right endpoint of the line down to 80%.  Still straightline, a lossy method because he is cutting 20% of his tones, but it works for him.
So what I did was experiment with the two end points of the curve line going up and down and found that what I have on Malin's site was the best for all colors, tho yellow could be a tad different (same finding in PDN--yellow the outlier).  Then I printed Parking Lot like this, and it did take me more messing around with development but it works.
Oh, all ink negs on a 2400, but it worked the same on a Clarion (?) Epson printer with MIS inks, too.
Now, it isn't as un-technical as merely inverting a neg and printing it out on typing paper....or making a pinhole neg and using that :)
Christina Z. Anderson

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  • References:
    • Re: new gums
      • From: "Christina Z. Anderson" <zphoto@montana.net>
    • RE: new gums
      • From: Marek Matusz <marekmatusz@hotmail.com>