Powdered Food Grade Gum Arabic - Problems!

Discussion in 'Hand Coated Wet Prints' started by mxanderc, Dec 21, 2017.

  1. mxanderc

    mxanderc Member

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    Hi, I've been learning and working with gum printing for a little while now; long enough to get some really good prints, so I feel like I have the basic process down just fine, but I've been having trouble with getting this gum to work. My successful prints were all done using premixed gum from either Photographer's Formulary or this printmaker's supply who's name I can't remember (it's the stuff the university stocks). But, I bought a bag of this powdered food grade gum a few months back, and I have yet to successfully make a print with it. Not sure what I'm doing wrong, or if the fault is in the gum itself.

    Without having any specific instructions on hand at the time, when I first tried mixing it, I started with approximately 500mL of water and added a spoonful of the stuff to see what would happen. After finally getting it all mostly dissolved, I found the water to be extremely thickened by it - more like a thick gel than the thinner gum I was used to with the premixed stuff. So I kept adding water until I got a consistency that seemed about right. I don't have a means to measure the specific gravity, so I can't say if it was the typical 14 baume or not, but it seemed close at least. But when I tried printing with it, I got results similar to what was described in this thread: https://www.photrio.com/forum/threads/gum-quality.152570/ ie; the gum wouldn't come off at all.

    Fast forward several months, and after a few similar experiments and failures, I came to the conclusion that the problem was due to not using nearly enough gum! The "gum" that was refusing to come off the paper wasn't gum at all - I'm convinced this is almost pure paint! I think that by using too little gum in the mix, the overwhelming majority of the fluid was water - which after evaporating away, left a tiny bit of gum, and alot of paint.

    So now I'm trying to determine how exactly to mix this gum and get both the right consistency so it's not too thick, while also having enough gum in the mix to make sure there's something proper for the paint to be bound up with and the dichromate to react to. I haven't been able to find good serious instructions anywhere about using this powder, except for some people saying "mix it 1:1 or 1:2 with water". For my latest experiment, I tried mixing 1:1 with water and the result wasn't enough water to even hydrate all the powder. So I added the same amount of water again to bring it up to 1:2, and after sitting for several days (I found this works much better than stirring it like a madman) the result is a very dense sticky glob that appears to be fully re-hydrated gum, but it would be impossible to try to print with it because it's so thick and viscous. The logical next step to me would be to add water until I get the consistency I want, but I'm afraid that by the time this glob is diluted enough to be usable for printing I will be back in the same old situation of the mix being mostly water without enough gum to be effective. Can anyone give advice about this? Anyone else successfully mixed up and printed with powdered food grade gum?

    Also, about preserving it. I have some sodium benzoate in dry powdered form, but I'm not sure how much needs to be added to prevent fungus growth. I tried it with a couple of my failed batches and mold grew anyway. And if I add too much, would that inhibit its ability to print?
     
  2. adelorenzo

    adelorenzo Subscriber

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    Use a baume hydrometer? The only cost about $40.
     
  3. OP
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    mxanderc

    mxanderc Member

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    Will that tell me if there's enough gum in it? I was having trouble with mixes that were extremely viscous and thick but yet didn't contain enough gum.
     
  4. Herzeleid

    Herzeleid Member

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    I mix 1+3 kordofan gum arabic powder and use it directly for gum print. I use 1+2 mix for grinding powdered pigment and making watercolor paint, it ends up like paste.
    Usually sodium benzoate strength for preserving is between % 0.01 and 0.5. It might be overkill but I use 0.5gr of benzoate per 100ml of gum arabic.
    I have 4 years old gum working properly.

    I have tested different gum arabic powders. I find 1+3 is overall good concentration for printing and mixing with tube water colors.
     
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    mxanderc

    mxanderc Member

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    Thanks for the reply. When you mix it 1+3, do you find it needs to sit for a long time to fully rehydrate? How thick is the resulting mix?
    I've just taken the dense glob that resulted from my 1:2 mix and set that in some more water to see what I get. This water also had more sodium benzoate added to it.
    Just so everyone knows what's happening with this current batch: it started as 1/4cup powdered gum + 1/2cup water + 1Tbs sodium benzoate. After sitting in a covered container for over a week, it is now a heavy dense blob of gum that seems unsuitable for anything. I am certain a fair amount of the water has evaporated out - it seems like a very rubbery consistency. A tiny bit of visible mold has begun to grow on the side of the container. The gum itself doesn't smell sour; still has the sweet gum smell. I've now put this mass in a jar (discarding the moldy bit) and added 1cup of water with about 2Tbs of sodium benzoate dissolved in it. We shall see what it looks like tomorrow...
     
  6. Herzeleid

    Herzeleid Member

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    I often use a blender to mix powder completely, but it makes lots of bubbles. If I don't use a blender I occasionally mix the solution it takes a whole day. So either case I leave the solution for a day. In a covered container.
    I think the viscosity is identical to the ready product which is 14 be.
     
  7. ced

    ced Member

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    Hello! I have no experience with food gum but have mixed a few batches of crystal and lumps of acacia gum. Most info on the web says 300grms to a litre of water +/-1:3.
    I have had lots of problems getting a standard good for me and if you look on the web too the SG is between 12° - 17° Be!! I think the gum used in the printing industry is 14°Be.
    I have tried as low as 11°Be but settled on 12°Be. I think temperature/humidity plays a big roll in getting a smooth coating. Important I think to get yourself a hydrometer to be consistent, look for one that will
    give a reading of 1.000-1.150 SG. mine is only up to 1.120 (good enough for me) it was not so expensive and can be found in places that sell brewing/wine making equipment.
    1Tbs of sodium benzoate is too much. Serdar is probably right with the correct amount at 0.5gr per 100ml.
     
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