U of S | Mailing List Archive | alt-photo-process-l | Re: gum thickness and French check

Re: gum thickness and French check


I share your pain. Loosing large pieces of work in no fun. As far as presrinking I aways do that. It is so instructive to take a large piece of paper that you want to work with, mark it on two edges, soak in water for a while and dry. I use room temperature water. It is amazing how much paper shrinks. Most of the machine made papers shrink dfferently accross and along the edge. If you think how many hours you will spend making a print what is one little extra step in processing?


From:  "Christina Z. Anderson" <zphoto@montana.net>
Reply-To:  alt-photo-process-l@usask.ca
To:  alt-photo-process-l@usask.ca
Subject:  Re: gum thickness and French check
Date:  Mon, 20 Nov 2006 08:55:29 -0700
>Thank you, Jean!  So that means a true 60% gum solution and not a
>37.5%! Wow.
>Ha, ha, over the weekend I was piddling around in a bunch of
>different gum experiments while printing and I finally observed this
>one thing I had read about.  In the German books I have had
>translated for me, there was a term "flagging" which for the life of
>me I never knew what it was.  I even asked my original gum teacher
>(who is Austrian) what it is and he explained it to me but I had
>never observed it.
>This weekend I accidentally forgot to add the water part of the
>equation to my gum/pigment/di mix (I don't use am di at 30%, but cut
>it with an equal amount of water so it comes out to a 15% am di).
>When the gum prints went into the water for development I finally
>observed "flagging".  The layer, instead of flaking off as I usually
>see happen, came off in a chunk here and there, and at the edge of
>the chunk there were these little tears of wavy veils that waved
>like little flags!  It was worth ruining three large gum prints to
>observe this--and, technically I didn't waste anything but time
>because I just brushed the whole layer off.
>Speaking of ruining prints, I did so to 8 large prints over the last
>week for various reasons.  I sized unshrunk Rives BFK and FAEW and
>printed on it, thinking it would be dimensionally stable as I have
>read. NOT.  Both papers shrink 1/16 inch horizontally and vertically
>so I will NEVER again skip the shrinking step.  Those were ruined.  
>Maybe with small prints this is fine, or in a humid climate, but
>16x20 in MT, even with sponging the back of the prints with water,
>not for this babe. Besides, the shrinking step with a bunch of baby
>hangers and a shower pole is not a biggie.
>Second, I got this hairbrained idea to try out a yellow ink only
>negative--yellow being oddly enough a very dense pigment to UV
>light.  Well guess what--the second coat, have you ever tried to see
>registration with a yellow negative on top of a blue layer?  Don't
>try it.  4 more large prints in the trash along with 3 large pieces
>of Pictorico. Impossible.
>Third, I decided to coat a couple sheets of paper with a layer while
>my negative was printing out, thinking I would be accurate with the
>size of the layer area.  When I went to print, my coated area was
>not long enough. Tried to resurrect it with another layer.  In the
>trash. Oh well.
>Christina Z. Anderson
>Assistant Professor
>Photo Option Coordinator
>Montana State University
>Visual Communications Building Room 220
>Box 173350
>Bozeman Montana 59718
>----- Original Message ----- From: "Jean Daubas"
>To: <alt-photo-process-l@usask.ca>
>Sent: Monday, November 20, 2006 8:10 AM
>Subject: Re: gum thickness and French check
>>Hi Christina !
>>Replying about your question about the French expression "pour
>>For me, there's no doubt it means the final percentage of combined
>>products :
>>-  the solution "40 pour cent"  means :  a total 100 ml of combined
>>solution contains 40 g
>>- in the same manner, the "10 pour 100 "potassium dichromate means
>>a total of 100 of combined solution contains 10 of the chemical...
>>Hope it helps...
>>Cheeers from France
>>Jean Daubas
>>----- Original Message ----- From: "Christina Z. Anderson"
>>To: "Alt, List" <alt-photo-process-L@usask.ca>
>>Sent: Saturday, November 18, 2006 3:51 PM
>>Subject: gum thickness and French check
>>>One of the items that I have been looking into is the thickness of
>>>solution--when 14 baume (288g gum arabic per liter) became "the
>>>norm". Gum
>>>solution seems to have gotten thinner through the years.  Back
>>>around 1900
>>>it was more often "2 in 5",  40 g to 100ml, and as high as 60g to
>>>100ml. I
>>>measured this out and when adding 60g to 100ml you get about
>>>155-160 ml of
>>>combined solution, so essentially that would translate to the
>>>equivalent of
>>>375g gum arabic in 1000ml water--30% more than the 288g/1000ml
>>>considered 14
>>>baume. They're still mixing it at time of use 1:1 with dichromate.
>>>I finally received a copy of the very first gum book ever--Rouille
>>>Sepia-Photo et Sanguine-Photo, 1894.  How fun to read this.  In
>>>there the
>>>solution is "40 pour 100".  I want to make sure I am correct in my
>>>assumption that this means to add 40 grams to 100ml (resulting in
>>>a combined
>>>solution of 140ml) and not a combined solution of 100ml.  Is this
>>>how a
>>>French chemist would state it nowadays? It also says to make a
>>>potassium dichromate at "10 pour 100".
>>>I routinely use a thicker gum when doing my gum prints anyway,
>>>preferring to
>>>mix it from scratch.  However, I have a couple liters of
>>>commercial gum that
>>>I have been using up and the thickness between a 60/160 and a
>>>288/1000 is
>>>Also, as of late I have found a number of unusable pigments listed
>>>chrome yellow--that was recommended) with these gum printers.  
>>>One, "blanc
>>>d'argent", was said to, in a number of sources a. prevent
>>>(Rouille Ladeveze)  b. darken and c. hold onto dichromate stain
>>>and turn
>>>yellow (German texts). So I guess the "certain pigments don't
>>>work" started
>>>at the beginning of time...and since we don't have certain of
>>>these anymore,
>>>it is a moot point. Blanc d'argent is lead white or flake
>>>white...I can't
>>>seem to find it in a watercolor paint.
>>>Christina Z. Anderson
>>>Assistant Professor
>>>Photo Option Coordinator
>>>Montana State University
>>>Visual Communications Building Room 220
>>>Box 173350
>>>Bozeman Montana 59718

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