[alt-photo] Re: Gum solution help needed

[Katharine Thayer]

On Aug 8, 2010, at 6:57 AM, Philippe Berger wrote:

> Attention: The old solution of Gum is very better of a new solution  
> of Gum
> Why ???? because a old solution of Gum is more acid and it is very  
> better for the picture
> For me the best gum solution is after 3 month of prepare
> For my self, i use my best gum with old solution of Gum of 1 year  
> ago, i certifie it is very very best
>
> Sorry for my englis but
> A old solution of gum (3 month) is the best because the acidity is  
> important
> The French Photograph Demachy use only old solution of gum

Phillipe, do you have a reference for this assertion that Demachy  
used only old gum?  In Maskell & Demachy, 1898, which as far as I  
know is the most comprehensive summary of Demachy's methods,  he  
certainly doesn't suggest that he uses old gum, in fact quite the  
contrary; he recommends mixing up fresh gum every time you coat  
paper.   He stresses that freshly made gum gives the maximum  
solubility, a quality which he values highly  since he suspects  that  
gum's mellowness and softness is probably a result of its "superior  
solubity, which allows the insolated coating of colour to melt and  
run down, as it were, and form a kind of pate."  I don't know if  
there's any scientific basis for that belief, but that's what he  
believed.  He went on to say, "A solution of gum rapidly becomes  
sour, and it is important for us to know the degree of solubility it  
possess.  Although, therefore, the addition of a preservative (such  
as a few drops of choloroform water) may arrest the tendency to  
acidity, the safest plan is to use fresh-made solution for every  
batch of papers to be coated, and thus be in possession of a standard  
quality which will save us much trouble in exposure or development."

Do you have a later source where he changes his mind about that?

Katharine