U of S | Mailing List Archive | alt-photo-process-l | Re: gum arabic

Re: gum arabic

Sorry, I should have all of the thread before I asked the question.

On Thu, Jan 29, 2009 at 7:57 AM, Keith Gerling <keith.gerling@gmail.com> wrote:
> Can anyone explain what a user might notice if she was using a poorer
> quality gum?  In the experience of the users, how does the pedigree pf
> the gum affect the print or the process of printing?
> On Sat, Jan 17, 2009 at 11:56 AM, Katharine Thayer <kthayer@pacifier.com> wrote:
>> P.S. The term "gum arabic" is used rather loosely, sometimes to refer to
>> acacia senegal, sometimes to gum acacia of any variety, and sometimes even
>> to other species, so I wouldn't put too much faith in the term "gum arabic"
>>  as being synonymous with acacia senegal.
>> kt
>> On Jan 17, 2009, at 9:18 AM, Alberto Novo wrote:
>>>> Also, sort is important;  the kordofan, labeled (1)  will be a higher
>>>> (finer) sort than the other, at sort 3.  Hope that's  helpful,
>>>> Katharine
>>> As for Kremer's gum arabic, their pdf on their gum details is the same for
>>> the three qualities, though their prices are different, so I am wondering
>>> what they really are. I am not buying from Kremer, because I have about 1 kg
>>> of gum arabic of unknown origin since a long time (though it works well).
>>> About Acacia senegal (cited from Kremer pdf):
>>> "Gum Arabic is a dried exudate obtained from the stems and branches of
>>> Acacia senegal (L.) Willdenow or closely related species of Acacia (fam.
>>> Leguminosae). A. seyal is a closely related species. Gum arabic consists
>>> mainly of high-molecular weight polysaccharides and their calcium,
>>> magnesium, and potassium salts, which on hydrolysis yield arabinose,
>>> galactose, rhamnose, and glucuronic acid. Items of commerce may contain
>>> extraneous materials such as sand and pieces of bark which must be removed
>>> before use in food. Gum arabic from A. seyal is sometimes referred to as gum
>>> talha."
>>> "Gum Arabic from A. senegal is a pale white to orange-brown solid, which
>>> breaks with a glassy fracture. The best grades are in the form of whole,
>>> spheroidal tears of varying size with a matte surface texture. When ground,
>>> the pieces are paler and have a glassy appearance. Gum from other acacia
>>> species may not have the characteristic tear shape and are often darker in
>>> colour. Gum from A. seyal is more brittle than the hard tears of A.
>>> senegal."
>>> One among the differencies (not easily testable at home) is their optical
>>> properties: water solutions from A. senegal are levorotatory, from A. are
>>> dextrorotatory.
>>> Alberto

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