[alt-photo] Re: evaporation of gum mixture

[Katharine Thayer]

Hmm, that's interesting.  I know nothing about what Formulary is  
selling for gum now, since I quit buying gum from them when they  
switched from a gum I really loved to a dark gummy gum for their  
premium gum and continued charging a premium price for it.  That was  
some years back, and as I said, I know nothing of their present gum.   
The only gum I've seen this happen with is Daniel Smith premium gum,  
and it's been a continuing problem with DS gum since I started using  
it 3-4 years ago.  Exact same containers  that I've always kept my  
gum-pigment mix in, but with other gums I've never had this  
evaporation problem.  With the Daniel Smith gum it's so pronounced  
that  the mixes have become  more viscous within a short time and  
dried out altogether within a few months, so I've had to throw out  
the mixes, which is very annoying because it's extremely wasteful of  
pigment.  In the beginning,  I thought it was because the workshop in  
which I was doing gum  at the time  I switched to Daniel Smith had a  
bank of west-facing windows that didn't open, and it got very hot in  
there on summer afternoons.  But the problem continued unchanged when  
I moved to my present digs, where the gum workroom is in a cool  
basement, so I'm convinced it's the gum (and besides, mixes made with  
other gums and stored in the same containers survived that hot  
workroom quite well and remain  fresh and nicely pourable to this day).

Whether you can reverse the problem by adding water is  a good  
question;  in my case,  by the time I noticed the increased  
viscosity, it was too late; adding water usually wasn't a  
satisfactory solution because the mix had gotten gummier and the  
water didn't mix in well.   But if you catch it fast enough, as  
you're doing by measuring the loss, it seems as if it should work.

Hope any of that is helpful,
katharine




On Jul 2, 2010, at 1:00 PM, Paul Viapiano wrote:

> Formulary, til present.
>
> Then, will switch to DS.
>
> p
>
> ----- Original Message ----- From: "Katharine Thayer"  
> <kthayer at pacifier.com>
> To: "The alternative photographic processes mailing list" <alt- 
> photo-process-list at lists.altphotolist.org>
> Sent: Friday, July 02, 2010 12:54 PM
> Subject: [alt-photo] Re: evaporation of gum mixture
>
>
>
>> Paul, what gum are you using?
>>
>>
>> On Jul 2, 2010, at 11:51 AM, Paul Viapiano wrote:
>>
>>
>>> Hello all...
>>>
>>> Having traced my pt/pd to a highly alkaline batch of Fabriano ,  
>>> I  have another question on an entirely different subject.
>>>
>>> Sometimes I make these little premixtures of watercolor pigment  
>>> and  gum arabic, nice and handy for printing tricolors in the  
>>> same  pigments. I mix about 1 gram pigment to 9 ml of gum.
>>>
>>> In May, I made a mixture and weighed it at 17.9 grams in its   
>>> plastic snap-cap container. Two months later, it weighs in at  
>>> 17.2  grams. What is it that is evaporating? Gum arabic? I'm  
>>> curious...
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>>>
>>>
>>
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