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  1. #1

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    Using CMC as sizing or gum substitute

    Hi folks,
    As a production potter for 20+ years I use CMC (carboxymethylcellulose) in my glazes and slips as a defloculant and hardener/binder. Gum Arabic substitutes well in these applications. I have pounds of the CMC powder and was wondering if any of the chemistry minded folks on the forum would know if it can be used in place of gum arabic for gum prints or perhaps used as a sizing agent with some kind of hardener if needed (glyoxal etc) for any papers that require sizing for any of the various alternative processes? Maybe in a salt print substituting cmc for gelatin?

    I tried a gum print today with cmc instead of gum and I barely got an image but the stuff was very durable with holding onto the paper and wouldn't wash off the paper like gum does. Is it worth experimenting or am I wasting my time? Just looking for another use for this stuff if it's applicable.
    thanks for any opinions given!
    regards
    Erik

  2. #2

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    Erik-Sounds like the crosslinking is interfering with the pigment adsorption into the matrix. Two ideas-1)try a different pigment brand. Some pigment cariers will react with the dichromate and some will not. You can test this easily. Just mix a drop of dichromate solution directly with pure pigment concentrate from the tube. Let it dry. expose half of it and wash.
    2) an absorption carier, like arrowroot starch, mixed with the CMC/pigment/ dicromate mix.
    I could be off base here. It may be incompatability of the pigment or carrier with CMC. Then a different brand of pigment may help.
    Bill

  3. #3

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    Quote Originally Posted by wildbillbugman View Post
    Erik-Sounds like the crosslinking is interfering with the pigment adsorption into the matrix. Two ideas-1)try a different pigment brand. Some pigment cariers will react with the dichromate and some will not. You can test this easily. Just mix a drop of dichromate solution directly with pure pigment concentrate from the tube. Let it dry. expose half of it and wash.
    2) an absorption carier, like arrowroot starch, mixed with the CMC/pigment/ dicromate mix.
    I could be off base here. It may be incompatability of the pigment or carrier with CMC. Then a different brand of pigment may help.
    Bill
    Thanks Bill for the suggestions. I was using a Senellier blue pigment. I'll try another and see what happens.

    Do you know if cmc will harden sufficiently to perform as a size or will perform adequately for example a salt print coating? I'm not a chemist but am willing to learn
    regards
    Erik

  4. #4
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    I think that CMC "hardens" by a different method than most materials. It has 1 or 2 free organic acid groups per repeating unit, that can form a salt with some divalent ions or trivalent ions. So, Ca ++ or Mg ++ (Calcium or Magnesium) or Al +++ (Aluminum) can appear to crosslink CMS.

    PE

  5. #5

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    Quote Originally Posted by Photo Engineer View Post
    I think that CMC "hardens" by a different method than most materials. It has 1 or 2 free organic acid groups per repeating unit, that can form a salt with some divalent ions or trivalent ions. So, Ca ++ or Mg ++ (Calcium or Magnesium) or Al +++ (Aluminum) can appear to crosslink CMS.

    PE
    Thanks PE, even though I don't understand a thing you wrote Are you saying I cannot easily use it for sizing or coating are you saying it will work just fine as long as I use CA, MG, or AL of some sort? I really wish I had payed more attention to Mr. Marek back in my high school chemistry class!
    regards
    Erik

  6. #6
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    Erik,

    I'd really like to know the answer to this question also. I tried to use CMC gum as a transparent/inert binding for two sheets of film but I found that it was too strong and didn't dissolve very well, which was a problem because it was meant to be a temporary adhesive.

    For instance, if you let a drop dry on your counter, it dries very hard and is difficult to get off. This would suggest that it might be an excellent substrate/sizing though.

    Why don't you coat some different concenctrations on a piece of tissue paper, let it dry and see if it dissolves as is? I suspect that even this might be difficult.

    Last thing I'll say is that I know of one patent wherein a very dilute solution of CMC gum is coated over a gelatin layer to produce an overcoat that inhibits the migration of mordants from the gelatin layer. This is for a dye-imbibition paper. So, it must be pervious to the dyes, but not this particular mordant.

    It's an interesting substance, I'd like to know more about it.
    If you are the big tree, we are the small axe

  7. #7
    Photo Engineer's Avatar
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    I'm sorry that I can not give a definitive answer to this as I have not tried it myself. I've used CMC as a thickener in "goo" for instant products, and for spreadable process solutions. I've also used it in gelatin as a thickener. In all of this, I've found, under my conditions, that the CMC redissolves when wetted if it dries down. So, all I can give you is theory here.

    If you have (as you do in CMC) R - COOH (this is the symbol for an organic acid) and it meets with a Ca++ ion (or other ion with multiple plus charges), you can get R-COO Ca OOC-R + 2H+ which is a cross linked (hardened) molecule where R = the rest of the CMC molecule or molecules.

    At present, I have no CMC in the lab so I can't test things and give a better answer.

    PE

  8. #8
    holmburgers's Avatar
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    Haven't really read it yet, but this might be a very good read.

    Methylcellulose & Sodium Carboxymethylcellulose: Uses in Paper Conservation
    - http://cool.conservation-us.org/cool...1/bp01-04.html
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  9. #9
    holmburgers's Avatar
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    This is curious, "The adhesive dries to a very thin even layer and is easily reversible with cold water. It is non-staining and does not become brittle upon ageing. Other applications in this section might include temporary facings, mends or backings. If you can use hot water for a wash bath, you might like to use MC as the temporary adhesive as it will not dissolve in hot water but is easily reversed in cold water. "

    This specifically applies to methylcellulose, whereas sodium carboxy methylcellulose (CMC gum) is soluble in either hot or cold water.
    Last edited by holmburgers; 08-29-2011 at 01:48 PM. Click to view previous post history.
    If you are the big tree, we are the small axe

  10. #10

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    PE, in theory can i add a little whiting to a 1% cmc solution to make the cmc "harden" and become insoluble in water similar to adding glyoxal to gelatin? it would be nice to not have to use glyoxal or heat up gelatin to size papers with. It coats very nice and dries relatively fast and would be a nice substitute. I know you can't answer definitively because you can't test it yourself but is the "theory" sound?

    Holmburgers, I know what you mean about it making a nice glue. Sometimes at work I have to use a pipe wrench to open the screw top lid that I store the cmc solution in for my glazes
    I did read that paper conservation article you referenced while I was googling cmc. It seems to have many uses but doesn't seem to have many practitioners in the alt photo world - there must be a reason...

    regards
    Erik

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