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

[gumprint at gmail.com]

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
>
>
> _______________________________________________
> Alt-photo-process-list | http://altphotolist.org/listinfo
>



-- 
*Carole Hollander*