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

[Darkrooms, Department of Art]

Diana,

Thanks for your reply.

I do use the unit for the other processes.  These are the exposure times I
am getting for use with digital negatives:
Cyanotype:  30 minutes
VanDyke Brown: 10 minutes
NA2 Platinum: 8 minutes

I had the same feeling that I should not need such a long exposure and
that over 10 minutes would be long.  I am starting to wonder if I should
not be expecting to clear the Base+fog in one printing.  When I compare my
time results test to a Macbeth 5 step grey scale 4 minutes is
approximately the density of step two and 8 minutes is approximately step
three.

I should also add that I mixed the Potassium Dichromate 3 years ago and
the Ammonium Dichromate 2 years ago.  Should I mix new?

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








On 3/7/13 11:15 AM, "Diana Bloomfield" <dlhbloomfield at gmail.com> wrote:

>Hey Jennifer,
>
>Other people will jump in here and surely have better suggestions for
>you--  but just reading this over-- I would have said that your main
>issue might be the lights (?). That seems like  extraordinarily long
>times for exposure.  Maybe you're just doing a lot of testing, and I'm
>just confused-- and whatever you're doing is way over my head-- but do
>you use this same unit for the other processes you mention, with no
>problems? 
>
>Diana
>
>On Mar 7, 2013, at 10:58 AM, Darkrooms, Department of Art 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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