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  1. #1
    holmburgers's Avatar
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    AZIDE Carbon Printing Sensitizer - Amazing Dichromate Alternative!

    If you're not familiar with 4,4'-Diazidostilbene-2,2'-disulfonic acid, disodium salt, tetrahydrate, it's much easier to call it DAS, or the amazing azide sensitizer that was used in the UltraStable process and which is currently being used by the world's leading color-carbon printer, Tod Gangler.

    This sensitizer is a non-carcinogenic and non-toxic alternative to the dichromates historically used in carbon printing (potassium, ammonium, etc.) and similar processes (gum, PVA, probably more). In addition to being environmentally friendly and safe to work with, it has no "dark reaction" like the dichromates. What this means it that tissues can be made with incorporated sensitizer (pre-sensitized) and they will keep for long periods of time. UltraStable tissues from the mid-90's will still make prints today.

    Although I can't give any hard facts or guarantees at the moment, all the information we've been seeing tells us that pre-sensitized tissues should keep on the scale of years, depending on humidity and temperature. Refrigerated tissues should keep well for several years and frozen tissues... who knows.

    Differences in working technique with DAS are minimal. The manner in which the sensitizer is incorporated into pigmented gelatin or "glop" is elucidated here, and there is a simple clearing bath (here) which uses a minute amount of potassium permanganate. Also, the sensitizer powder should be refrigerated and kept away from light. With refrigeration it will keep well, even better with freezing (the manufacturer has kept this stock frozen since 2006 and its properties have not changed). Detailed information about the sensitizer will be included with all orders.

    As an incorporated sensitizer it's recommended to use DAS at 0.6% as a starting point. For 500mL of pigmented gelatin, that's only 3 grams of sensitizer. Contrast is affected by changes in sensitizer concentration, just like dichromates. I believe that printing times are generally a bit longer however. DAS is sensitive to UV light just like the dichromates (its sensitivity peak is 335nm).

    Tod Gangler personally tested this batch of sensitizer and gave it his approval. A great debt is owed to Tod and Charles Berger for sharing their experience with this sensitizer amongst the carbon community. Many others here on APUG have done a lot of digging, reading and experimenting to pave the way for this group buy; many thanks to them too! (you know who you are ) This thread has been the clearing house for most of this information.

    ------------------------------------------------------------------------------------------------------

    The price is 20¢/gram, or $200/kg, plus shipping & packaging (email me for an estimate). International shipping is welcome! This chemical is not considered hazardous by any international transit authority and should not cause troubles. However, I recommend that you attempt to confirm that this is the case in your country if at all possible, just as a precaution. The CAS# is 2718-90-3.

    The minimum quantity is 100 grams and international orders are limited to 1kg. I would prefer check or money order on domestic orders, but Paypal is OK with a little bit extra to cover the fees.

    The DEADLINE for this order is January 27th at 11PM EST. This is when I will be placing the final order with the supplier and also for the packaging supplies. This means that orders won't be shipped until a couple of weeks into February. I apologize for this long delay, but it's the nature of this wholesale buy and the fact that I have to repackage it.

    This is a rare opportunity to get in on the ground floor of a revolution in alternative processes! There will of course be a learning curve, but the beauty of this group buy is that it will put the sensitizer in the hands of many people for the first time at once, and as a community we can all learn collectively how best to approach this new way of working.

    Please do not PM me if you can help it; email is a much more reliable method of communication for me these days - holmburgers(at)yahoo(dot)com

    2% of classifieds sales go to APUG.

    Thank you!

    Chris H.
    If you are the big tree, we are the small axe

  2. #2
    mdm
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    I am still waiting for a reply from you about shipping to here, as soon as I get one you will get paid but not until then.

    Ok i see you have answered my question.
    Last edited by mdm; 01-14-2013 at 11:24 PM. Click to view previous post history.

  3. #3
    holmburgers's Avatar
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    Although it's taken a while to get back to everyone involved since the beginning of this, I've gotten caught up now. If you send me an email I will respond quickly.

    Thanks mdm,
    If you are the big tree, we are the small axe

  4. #4
    holmburgers's Avatar
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    APUG member keesbran has reported trouble using gum; so please, if you're interested in its use for gum, please be ready to experiment, it may not be a drop in replacement. I apologize for giving conflicting statements in the first post.

    Kees also shared a note about refrigeration. From the freezer, DAS should be acclimated first in the refrigerator for 24 hours, and then at room temperature for "several" hours before opening. Condensation will harm it.

    I learned from the supplier that DAS is prepared for industry with 3% water content. This compound is flammable if completely dessicated, but because of its 3% moisture content it is completely safe for normal handling. Basically, just don't expose DAS to open flames or hot surfaces.
    If you are the big tree, we are the small axe

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    Stability in alkaline environment?

    I found that the speedball diazo sensitizer looses all of its sensitivity in less than a 1/2 hour in an alkaline casein emulsion but I don't have specifics on pH, only that this alkaline environment has this effect. From what I understand, the pH reducing phosphoric acid in this particular speedball sensitizer is necessary for stability but this is not compatible with casein.

    The question then is: Does DAS have an "acidic environment" requirement? Does anyone know of its stable working pH range?

    Also, can a working solution of DAS in water be stored in the fridge for later use?

    Peter Friedrichsen
    Last edited by PGum; 01-23-2013 at 06:32 AM. Click to view previous post history.

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    Quote Originally Posted by PGum View Post

    The question then is: Does DAS have an "acidic environment" requirement?

    Peter Friedrichsen
    Hi Peter,

    Short answer: as far as my tests go, no it doesn't. I have used it with casein in the same way as I do with dichromates: mix the sensitizer just before use. I have not yet incorporated it directly. But sensitized sheets keep very well. After 3 days I see no difference in sensitivity or any stain. The speedball stuff is probably a diazo and this is not the same as DAS.
    DAS does not work with gum arabic.

    I keep my DAS 3% solution in a brown bottle in the dark, but outside the fridge. It keeps very well in my observation.

    kees

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    Peter, I can now answer your question with a more firm no! I made a sensitizer by mixing 2 parts of a casein/pigment mix with 1 part of a 3% DAS solution. With this mix I prepared 1 sheet of paper and dried it for 30 min in the dark at 45% RH. After this it was exposed with a step wedge for 1 minute under a bank of UV TL. It is 'developed' in water at 20° C for 30 minutes.

    The rest of the mix I kept in the dark at room temperature for 1 hour. After 1 hour I prepared another sheet and also dried it for 30 minutes at the same conditions as the first sheet. Exposure time and wash time were the same as for the first print.

    No visible difference can be seen between the two prints! I will examine them with the densitometer when dry, but I think we can safely say the alkaline environment makes no differnce. You may also note that an exposure time of 1 minute is about 4x faster than casein with dichromates. Currently I am also testing synthetic colloïds. With one colloïd I came in the 5s (!) range for a maximum black.

    My casein mix was made by soaking 4 gram of casein powder (kremerpigmente.de) in 35ml water for one hour. After this soaking time 1 gram of ammoniumcarbonate is mixed in and the mix is slightly heated until all carbondioxide is evaporated. I mixed in 2 gr. of lampblack watercolor paint.

    -kees

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    Quote Originally Posted by PGum View Post
    Also, can a working solution of DAS in water be stored in the fridge for later use?
    Possibly not. DAS has a low solubility (3% or 3g / 100ml of water at room temperature). Refrigerating the solution will drive some of that out of solution. You'll have to make sure that it comes back up to room temperature and that everything is re-dissolved before use. That's hard to do while mnimizing exposure to light, IMO.

    It is probably best to plan on storing this as a dry powder.

    --Greg

  9. #9

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    Quote Originally Posted by gmikol View Post
    Possibly not. DAS has a low solubility (3% or 3g / 100ml of water at room temperature). Refrigerating the solution will drive some of that out of solution. You'll have to make sure that it comes back up to room temperature and that everything is re-dissolved before use. That's hard to do while mnimizing exposure to light, IMO.

    It is probably best to plan on storing this as a dry powder.

    --Greg

    Keeping a working solution at room temperature for several months , in a brown glass bottle in a cupboard that is most of the time closed, showed no adverse effects for me. Nor any sensitivity change or crystallization.

    -k

  10. #10

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    DAS alcohol solubility?

    The free acid salt of DAS (sodium free) seems only to be soluble in some alcohols such as ethanol but not water, so I guess it is possible that DAS may also be soluble in alcohol. If so, one could make an alcoholic solution and if soluble enough, store it in the fridge. Of course this may be unnecessary if the shelf-life reported by Kees is repeatable.

    If a rich alcoholic solution is possible, then adding drops of this (with quick stirring) to a much larger emulsion volume may be a convenient way to incorporate higher amounts.

    Peter Friedrichsen

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