U of S | Mailing List Archive | alt-photo-process-l | Re: gum exposures with NuArc 26-1K?

Re: gum exposures with NuArc 26-1K?

Progress so far:

due to ease of availability (pretty much what I had on hand) I'm using the following:

Varn 100% Gum Arabic Solution. I did some digging, some people like it for Gum work, others hate it, this can is a very, very light amber and so far, (4 prints) I've had no staining.

Potassium Bichromate

W&N and Grumbacher Watercolours

I mixed a saturated solution of Pot. Di., added a bit of Lamp Black (I know, but the only Payne's Grey I have is an off brand and I wanted to at least not chase my tail, yet) to some Gum, stirred until in solution, added gum and Pot. Di. 1:1, coated some watercolour paper I had lying about. (probably Lanaquerelle 140# HP). let it dry and contact printed a 4x5 film neg with a CI of about 1.8. for 90 units on the NuArc Integrator (calibrated so when bulb is up to full output, 1 unit is 1 sec) First results are promising. Hadn't thought about paper or OHP negs (yet...) I'm just trying to reduce variables until I get as much of a hand on the process as I can. I can definately see digging up some contrasty 8x10 negs today and trying a few sheets though I'm still working out a consistent, easy to implement registration system that doesn't screw with the negs. Once I get this down, I'll probably do some enlarged negs of some 4x5 work I've wanted to print larger, I have a full 42" roll of N31P stashed as well as a bunch of sheets of N31P and various lith films that I've been able to get a handle on the CI after a few tests shots and have a somewhat workable methodology to get the desired CI, though most of the film I've been shooting has been destined for scanning and I've been processing for a CI of about 1.6 or so, so I can keep the film curve on the linear area of my scanners response curves. It would be trivial to get a CI of 2.5 or so, as my early attempts got me into that area accidentally. I can definately see that I will have to do multiple coatings to hold highlights and shadow, as so far (4 prints, all done last night, remember I'm a gum virgin) it seems to be an either or with my "standard" negatives. Any and all advice, criticisms, (beer, wine, coffee) will be greatly appreciated, as I'm trying to get a handle on gum and cyano before I start school (Finally decided after taking a year off in '81, and that the year surely must be up by now, that I really should get my BFA if I'm to get anywhere doing what I enjoy) and the more difficult of the two seemed like a sensible starting place to me.


Judy Seigel wrote:

On Sat, 26 May 2007, Erie Patsellis wrote:

Just as a sanity check, is anybody on the list exposing gum with a NuArc platemaker? what are your exposures running?
Do you think yours are too short or too long? Mine were always very close to exposures with the BL fluorescents as for a long time I used them interchangeably -- from 1 to 3 minutes. If yours seem long, is your glass clean? Have you cross-checked in sun... maybe your am di is too weak, or contaminated? Or negatives too dense? Gum needs density range of about 1 (IIRC, it's been a while since I measured.) Or are you mixing emulsion too far in advance? Or letting coated paper wait too long?

I also note that when I changed from film neg to paper neg (inkjet) exposure times were about half... or less. Paper doesn't have the built-in filters.

Good luck...


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