Re: Dichromated Gelatin Emulsions

The use of sugar as one of the ingredients of carbon tissue dates all the
way back to the beginning of the carbon process. The first mention to it I
know is in Swan's original patent of the carbon process from the 1860s. He
wrote: "In producing the photographic tissue refererred to, I form a
solution of gelatin, and for the purpose of imparting pliancy to the
resultant tissue, I have found it advisable to add to the gelatin solution
sugar or other saccharine matter, or glycerine."

In many formulas for carbon tissue from the 19th and early 20th centuries
sugar and/or various kinds of soap are substituted for sugar or glycerine,
without specifying the justification for such substances.

As far as I can determine from my own work with the carbon prpcess the only
benefit gained from the addition of sugar and/or glycerine is an increase
in pliancy. The addition of these substances does not appear to have any
affect on the working qualities of the tissue, i.e. they do not "help the
portions of the emulsion that weren't hardened dissolve or 'develop' more
readily." as Judy suggests, nor do they impact in any appreciable way the
sensitivity and contrast of the tissue. I can't say the same for soap since
I have never added it to tissue.

Sandy King

>On Wed, 6 Dec 2000, Art Kerbs wrote:
>
>> Good morning everybody, Need some help... researching dichromated
>> gelatin emulsions. I understand the reasons one add glycerin, but in
>> some of the formulas, of days gone past, sugar was also added. does
>> sugar do something that glycerin doesn't?? Why was sugar added? Many
>> thanks for your valued feed back Art
>
>As far as I know the sugar was supposed to help the portions of the
>emulsion that weren't hardened dissolve or "develop" more readily. The
>only formulas with sugar I've tried were with gum arabic, not gelatin, and
>in those the sugar in fact had no effect. This may be (another) one of
>those cases where the theory & the reality live separate lives. You'd
>have to test.
>
>There are also emulsions designed to remain sticky for dusting-on
>processes. Some of those have sugar of various kinds (I've seen rock
>candy called for) and/or honey.
>
>Good luck with the dichromated gelatin -- the world awaits !
>
>Judy
>
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>| World Journal of Post-Factory Photography > "HOW-TO and WHY"
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Received on Thu Dec 7 06:36:54 2000