Re: Gelatine is also '' a '' gum but not Gum.

Hear hear. The only quibble I might have is with the idea that top-
down hardening is the rule for all these processes; for gum, at
least, the jury is still out on top-down hardening.
Katharine

On Apr 4, 2006, at 8:55 AM, Sandy King wrote:

> A more appropriate generic name than gum would be direct
> dichromate colloid processes. This would included processes we
> commonly call Gum, gloy, PVA, direct carbon, Fresson, Artigue,
> Hochheimer Gum, Paper Noir Gomme, Tempera Print, Cassein, etc. and
> a bunch of others I forget.
>
> In general, although there are some important working differences,
> they all work on the same basic principle, ie. exposure (and
> hardening of the gelatin) is from top to bottom, with no transfer
> of the image (as in carbon and carbro). Also, many of these
> processes involve the use of more than one colloid, as was true of
> Fresson, Artigue and the many commercial gum papers that were once
> produced. You might mix gelatin with gum, or gelatin with fish
> glue, or fish glue with rabbit glue, or cassein with gum arabic,
> and blah, blah, blah for ever.
>
> And each mixture would give a slight variation in terms of working
> procedures and appearance, which would be, at least IMHO, a more
> interesting and useful topic for discussion than what this
> discussion has offered so far.
>
>
>
> Sandy
>
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>> Ha, John, been there, done that.
>>
>> It was an old method to "speed" gum up. What it did was create
>> stability in
>> the highlights, in other words, lotsa staining. The more acid, the
>> more
>> staining. But I can imagine that back in the day when they were
>> believing
>> that gum didn't give halftones and it produced "soot and chalk"
>> images, that
>> it was a good enough technique, especially with the variability in
>> negatives they might have had..
>>
>> I love those old gum recipes, additions of all sorts of stuff. I
>> just had
>> an old book translated for me from the German on the egg white gum
>> print, a
>> combo of the two. My translator has translated 4 such books now,
>> 4 more to
>> go. They are a HOOT, these old books.
>>
>> Do you think it is no longer a gum print, but an acetigum? A
>> gumacete?
>> Chris
>>
>>
>>
>>
>>> Just to complicate the issue further I read in one of my old
>>> photographic
>>> dictionaties that a very useful gum can be made by adding acetic
>>> acid to a
>>> solution of gum arabic.
>>> Have a nice Spring, yo all. John - Photographist - London.
>>>
>
>
Received on Tue Apr 4 10:19:13 2006