Re: daniel smith gum
I won't go into the relative merits of prepared commercial gums, since I prepare my gum from bulk. However, a couple of points:
1. Kremer is just citing the definition of gum arabic by the Joint Expert Committee on Food Additives (JECFA 1997): "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...". What this means exactly as to contents of the product I don't know, but as recently as 1978 there was a requisite of levorotation in the definition of gum arabic, which later disappeared. Of course, a solution of the sap of A. seyal is dextrorotary (rotates polarized light clockwise) so before 1978 this product was not considered "gum arabic". But today it is.
2. I have a small amount of Acacia seyal gum (called "talha" in Arabic), brought to me by a friend from someplace in southern Algeria. I prepared a gum solution with this talha a year back, but somehow never got to test it. So today, stimulated by this discussion, I put it to the test. The talha gum behaves the same as the more usual hashab (A. senegal) gum, it has more or less the same colour, the same consistency, no differences there. I read that it is more brittle, but once applied to the paper and dry, it looks the same.
The difference came after developing. I left it 30' in cold water, a standard develop time in my workflow, but when I looked at the paper, I was surprised: a very flat image, with all the symptoms of underexposure and tonal inversion in places. I resisted the temptation to throw it away and will make a full three-colour print to see what happens (I only did the yellow coat).
Conclusions? Well, I only made one single test, so there's pretty little I can say, but other tests pending I believe that talha is quite a different beast from the hashab gum we more commonly use. Next I will attempt another test, with longer exposure...
cheers Tom Sobota Madrid, Spain On Tue, Sep 29, 2009 at 9:01 PM, Katharine Thayer <kthayer@pacifier.com> wrote:
I looked up that previous discussion about how some gum arabic is not acacia senegal but acacia seyal. It was a link to a Kremer page supplied by Alberto Novo in January of this year that alerted me to the difference between acacia senegal and acacia seyal, the description of the brittleness of the dried acacia seyal making me wonder if perhaps the Daniel Smith premium gum may be at least partly acacia seyal.. I can't seem to find my way back to the exact Kremer page to link it directly, but here's a post where Alberto copied the relevant paragraph from the page:
http://www.usask.ca/lists/alt-photo-process-l/200901/msg00118.html
The fact that the Kremer price list at that time identified at least one of their gum arabics as a mixture of acacia senegal and acacia seyal, made me wonder even more whether Daniel Smith may also mix these two types of acacia, but was unable to get an answer to my question from Daniel Smith. Now the Kremer price list specifies that their powdered gum arabic is either acacia senegal OR acacia seyal, no way of knowing which one you're going to get.
The Daniel Smith premium gum does print very nicely, don't get me wrong, that's why I've kept with it in spite of my issues with some of its qualities, but it does have these odd qualities. My suspicion that it may be at least partly if not wholly acacia seyal instead of acacia senegal is just a speculation on my part, since I couldn't get an answer from Daniel Smith, but it's definitely not the same material as the other gums I've used. And I don't really know whether the powdered gum will turn out to have the same qualities as the liquid premium gum, but I'm hoping it won't. It would be helpful if they were more fothcoming about what gum(s) they are marketing under the product name "gum arabic."
Katharine
On Sep 27, 2009, at 9:45 PM, Katharine Thayer wrote:
Paul, like all answers in gum, "it depends"....
I don't care for the standard (dark) gum, mostly because I mix pigment/gum mixes by eye and I need the color and darkness of the gum not to obscure the color of the mixture. I also once believed someone's assertion that the dark color of the darker gums sullies the brightness of the colors in the finished print, but when I tested that assertiont, it turned out not to be so. But I did find that the darker gums,including the DS standard gum, tended to print with fewer steps (more contrasty) than the lighter gums.
I've been using the Daniel Smith premium gum exclusively for three-four years now, and I have a couple of issues with it. The pigment/gum mixtures I make with it seem to quickly become more viscous and before long, dry up altogether. This never happened with the old Formulary gum; I have mixtures of little-used colors made with it that I've had mixed for years and years, that are just as fresh as the day I mixed them. Generally my mixes made with this Daniel Smith premium gum are unusable within 6 months or so. This is a problem.
The gum also has a different quality than what I consider quality gum arabic, a brittleness that I saw when I brushed out unpigmented gum on a piece of paper and let it dry. Normal gum arabic, brushedout in a thin coat, dries smooth with a slight gloss; the DS premium gum is brittle when dry, and cracks or flakes (shatters, actually, is a better word to describe what it looks like) into shiny bits like tiny pieces of cellophane that no longer adhere to the paper. I've never seen this happen with the pigment mixed in, only with the plain gum. I don't know what this means, but a description I read somewhere of a slightly different type of gum, (not acacia senegal but a different variety) including that it's more brittle than acacia senegal, for example, sounded so much like the behavior of this gum that I began to suspect that this gum may be at least a mixture of acacia senegal and this other type of gum. I don't remember the particulars, like what variety of acacia this other gum is from, but I do remember that I wrote a post or two about it at the time, which should be found somewhere in the archives. I called Daniel Smith and asked, but no one could (or would) tell me anything. They make their own watercolor paint, and one might suppose that the gum arabic that they sell would be the same as the gum arabic that they use in their watercolor paint, and you would think that the people who make the paint would be able to answer that question, what variety of acacia their gum arabic comes from, but maybe they consider it a trade secret or something. At any rate, I've recently mixed up a batch of the gum they sell as powder, and while I haven't actually printed with it yet, just mixing it and working with it, feeling its character, it *feels* more like "gum" to me. We'll see. I'm really quite tired of having to toss out dried up cannisters of mixed gum/igment; it's a huge waste of pigment.
As to the Formulary, I don't know what they're selling now. I used to love their gum but when they started selling something resembling crankcase oil for their premium gum, I bailed out and haven't bought gum from them since. But since gum, like wine, changes from season to season, an observation made some time back is essentially useless now.
Katharine
On Sep 25, 2009, at 3:36 PM, Paul Viapiano wrote:
Daniel Smith gum...standard or premium light?
Is there a big difference between the two and is it much different than the Formulary gum?
Just curious...
Paul
|