[alt-photo] Re: Gum Printing: Looking for some wisdom

[Diana Bloomfield]

P.S.  I'll second the suggestion that you should by Chris's book-- a wealth of information.  And my exposure times for gum are typically 4-7 minutes.

Diana

On Mar 7, 2013, at 11:53 AM, gumprint at gmail.com wrote:

> Greetings Jennifer,
> 
> I have been making gumprints using a bank of 6 BLB 4" from the contact
> frame with both analog and digital negatives. My exposure time range from
> 30 seconds to 7 minutes, never more.
> In looking at your pigment dilutions I found them to be much different from
> what I have been using (since 1978). I am one of those people who tested
> all the Windsor and Newton tubed pigments (with dichromate) to determine
> staining and maximum pigment ratios. An emulsion made with 1/2 gram to 60
> ml of gum arabic is, to me, quite dilute. For lamp black I would typically
> use 1/2 gram to 10 ml of gum mixed 1:1 with a 15% solution of ammonium
> dichromate and use Fabriano Artistico (post factory sized) or Soft press
> FA. (I have to admit here that I never use WN lamp black because for me it
> stains when over 1/2 gram and at 1/2 gram it is too thin.) I develop in 80
> degree water for 15 minutes (face up for one minute first), changing the
> water 4 times for total of 1 hour.
> 
> As an aside, nearly all the pigments I use are 1/2 gram to 1 gram per 10ml
> gum, which I mix using a glass mortar and pestle so I am sure the pigment
> is in suspension. There are a lot of variables in printing gum and some of
> what you have not said may also be leading to your unusual results such as
> development water temperature, length of development, humidity, coating
> method and thickness, etc.
> 
> If your dichromate is dropping crystals it is likely over saturated. 30% is
> a saturated solution with ammonium dichromate and it will drop out if under
> 65 degrees. I would warm it in a hot water bath, not heat it directly.
> 
> With regard to the tanning effect, I think you may be seeing the gum arabic
> that has been rendered insoluble from the lengthly exposure.
> 
> I hope this helps. Feel free to write back if any of this is unclear.
> 
> Best,
> Carole Hollander
> 
> 
> 
> On Thu, Mar 7, 2013 at 10:58 AM, Darkrooms, Department of Art <
> darkroommanager at cornell.edu> wrote:
> 
>> Hello all,
>> 
>> I have been following this list serve for about two months now and what a
>> wealth of knowledge you all have!  I am hoping that you might give me some
>> words of guidance as I attempt to tackle gum printing.  Before I ask my
>> questions I would like to give a little background on how I will be using
>> this process and where I amŠ
>> 
>> I am the Photo Technician at Cornell University and we have been teaching
>> an alternative processes course using Litho and digital negatives.  This
>> past winter break I started using the quad tone rip and we are adding Gum
>> printing to the list of processes covered.  I have had fantastic results
>> creating negatives with Quad Tone RIP for Cyanotype, VanDyke Brown and NA2
>> Platinum.  I am just starting the process with Gum and having only dabbled
>> in gum briefly about 3 years ago I am getting a little tripped up with the
>> process.
>> 
>> So far I have completed the dot test that is outlined in the Keeper of the
>> light to determine Pigment to Gum ratios for each color I would like to
>> use.  I have completed this on both the Fabrino Soft Press (un-sized) that
>> was discussed a few weeks back and Rives BFK sized in Gelatin and hardened
>> with Glyoxal.  The dot test looked great and I am now moving on to
>> determining a base time for printing with pictorico.  I am starting my
>> tests with Winsor Newton lamp black 1/2g in 60ml of gum arabic mixed 1:1
>> with  Potassium dichromate and another with Ammonium Dichromate.  I
>> completed a time test with a strip of pictorico using 4 minute increments
>> up to 32 minutes with each sensitizer on both Fabrino and Rives paper.  I
>> am using a homemade exposure unit that consists of a bank of closely
>> spaced black light UV florescent tubes approximately 3 inches from the
>> exposing area.  The tests on both papers took overnight to completely
>> clear of the brownish coloring.  From what I have read some people are
>> able to obtain an exposure on a light table in less then 10 minutes.  My
>> tests show a distinct separation between the Base+Fog of the pictorico and
>> the uncovered areas of the print up through 32 mintues.  On the Fabrino
>> paper with Ammonium Dichromate at 32 minutes this difference is just
>> barely noticeable and my thought is that at about 35 minutes I surpass the
>> base+fog of the pictorico.  After about 12 minutes on all test some
>> tanning is appearing.  If I were to go with a 35 minute exposure tanning
>> is sure to be visible.
>> 
>> My questions are:
>> 1.  Should I try for longer exposures to see if I can obtain an exposure
>> sufficient to hide the Base+Fog of the pictorico and if so is there a
>> remedy to the tanning?
>> 2.  Should I adjust my mix of sensitizer?  I have mixed the Potassium
>> Dichromate in a way that it has a large amount of precipitated chem unless
>> heated to almost 100F (this was done at a professor's request).  I mixed
>> the Ammonium Dichromate as outlined in Sarah VanKeuren's Non-Silver
>> Manual, placing chemical in a graduate to reach the 1oz line and adding
>> water to 10oz.
>> 3.  Or do you have any other suggestions?
>> 
>> Thank you in advance for reading this long email and I am looking forward
>> to any words of wisdom you have to offer.
>> 
>> Best,
>> Jennifer Gioffre
>> Teaching Support Specialist
>> 
>> Architecture Art and Planning
>> Cornell University
>> 120 Tjaden Hall
>> Ithaca, NY 14853
>> 
>> Office: 607-255-4207
>> Fax: 607-255-3462
>> jmg393 at cornell.edu
>> darkroommanager at cornell.edu
>> 
>> 
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>> 
> 
> 
> 
> -- 
> *Carole Hollander*
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