A real Azo type formula

Discussion in 'Silver Gelatin Based Emulsion Making & Coating' started by Photo Engineer, Aug 25, 2007.

  1. Photo Engineer

    Photo Engineer Subscriber

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    This formula is similar to the Agfa Lupex and Kodak Azo papers when they used the old active gelatins. This would be about 1940.

    Part A:

    Gelatin (medium ripening) 3.5g
    Water 152.5 ml
    Egg White 7.5 ml (albumen - to add gloss)
    Sodium Chloride 2.5 g
    Sulfuric acid 0.5 ml (H2SO4 diluted to a density of 1.18)
    Rhodium chloride (0.1 g/ L) 0.1 ml

    Bring to 45 deg C.

    Part B:

    Silver Nitrate 5.0 g
    Water 80.0 ml

    Bring to 45 deg C.

    Add B -> A over 20 minutes at 45 degrees C.

    Add to this emulsion:

    Gelatin (hard ripening) 15 g
    Gelatin (medium ripening) 5 g

    Bring to 60 deg C and hold for 25 minutes so that these gelatins will melt fully.

    (NOTE: these two iodide steps can be combined in my experience)

    Add 1 cc of 0.65% KI and hold for 10 minutes

    Add 1.5 cc of 0.65% KI and hold for 10 minutes.

    (NOTE: this antifoggant/stabilzer below is very subject to crystallization in the emulsion causing problems. I have demonstrated it to my students. I have found better substitutes than this ancient compound, but hope to learn how to use it properly as it is good because it is very very inexpensive.)

    Add 0.5 ml of 1% Mercaptobenzothiazole in alcohol

    Stir 2 hours while slowly chilling and then wash.

    This yields a grade 2 Azo type paper.

    Now, the problems are these:

    1. We no longer have the 3 kinds of active gelatins avaialble to us.

    2. Silver Chloride emulsions were sensitive to these active gelatins and would keep poorly if not made correctly.

    Today, with inactive gelatins, this formula must be finshed with sulfur (from hypo as I described elsewhere on APUG) and even though this will be a useful substitute, the time and temperature must be carefully determined, and the emulsion is subject to poor keeping. Usually it turns out to be high in speed and contrast and will vary from batch to batch.

    The solution is to find the condition of precipitation in the absence of a sulfur finish which gives the right speed and contrast right from the outset with inactive gelatin and then it will keep very very well. This is what Kodak did with the 'ultimate' Azo paper, and what I have tried to do. Therefore, my formula and Kodak's do not resemble this older version of an Azo type paper.

    They both have good keeping and good speed and contrast from the time they are coated.

    But, this formula is a good starting point. At some future time, I will describe all of the reasons for the things that go on in the above formula and all of the things that can be done to improve on it.

    Have fun.

    Oh, and BTW, this shows that the early contact papers were AgClI emulsions, not pure AgCl emulsions.

    PE
     
  2. Bill Mitchell

    Bill Mitchell Member

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    Even when it was new, AZO was an ugly, green paper. I don't understand why anyone would want to reinvent it. Good ridance that it's gone, i say.
     
  3. nworth

    nworth Subscriber

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    What is the purpose of the rhodium chloride? The quantity is minuscule, but probably significant. A good thing, considering the price.
     
  4. Ian Grant

    Ian Grant Subscriber

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    Ron, this is almost exactly the Agfa Lupex "type" formula, Normal Grade, scaled down by a factor of 200 :smile:

    Except in the Agfa Formulae the Rhodium Chloride is in Part C (3) rather than in Part A (1) and the gelatin in Part D (4) has KI added, and is dissolved in water.

    In addition for the Normal grade paper both ripening times are 10mins at 60°C.

    Ian
     
  5. Photo Engineer

    Photo Engineer Subscriber

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    nworth;

    The Rhodium Chloride sharpens the toe of the paper.

    Ian;

    I'm aware of what you say and that is why I said that it is similar to both Azo and Lupex, as this formula is a workable hybrid of both and by either using sulfur sensitization and oxidized gelatin or adjusting addition times and temperatures, the 'correct' result will be gotten. So, based on the above formula, I have seen Azo type results from 4 distinct formulas. Three of them keep less well and are harder to control for speed and contrast than the one I have chosen.

    I have seen comments about the Rhodium Chloride being added just before pptn starts and others that state it should be run in partway into the pptn. This is another difference that I find in various formulas.

    This can be simplified considerably (as we did at Kodak). My own version is quick and simple.

    Bill;

    You may be right but everyone asks me about Azo type contact papers even though I can make many other types. And a lot of money is riding on M&Ps efforts.

    PE
     
  6. User Removed

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    Post any examples?
     
  7. Photo Engineer

    Photo Engineer Subscriber

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    Ryan;

    I have posted lots of them with my formula right here. It is a tweak and a simplification of the one above. The prints Alex Hawley did and his review used a very similar emulsion to this. It was altered using time and temperature as noted above to give the desired results with modern gelatin.

    PE
     
  8. Lachlan Young

    Lachlan Young Member

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    Just out of interest, why were active gelatins phased out?

    Thanks,

    Lachlan
     
  9. Photo Engineer

    Photo Engineer Subscriber

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    They were too variable and uncontrollable. In fact, EK was almost ruined by the famous (infamous) story of cattle eating mustard which made the gelatin extremely active and fogged the film. It was only then that Mees et. al. discovered that it was the allyl thiourea in the gelatin that caused the actual sensitivity increase in emulsions during making.

    The use of sulfur compounds and inactive (intert oxidized) gelatins are what ushered in the modern range of photo products.

    PE
     
  10. Donald Miller

    Donald Miller Member

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    Ron, With all of your knowledge of Azo, why are you not offering your formulas and your services to Michael Smith?
     
  11. Photo Engineer

    Photo Engineer Subscriber

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    Donald;

    You should ask Michael this question, not me. He is fully aware of my work and has seen my results.

    PE
     
  12. Michael A. Smith

    Michael A. Smith Subscriber

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    Quite some time ago, at the time we met with Ron Mowrey, and we had a very good meeting (for which we paid him at a fairly high rate, considering our means, though maybe not by some consulting standards), he said that his formula was not adequate to make a big production run. I do not know if the formula in this thread is the same one that he was working with when we met him. But, bless him, he did tell us where we might find a formula for a whole run of paper. And find it we did.

    We are pleased that he is now willing to generously share his formula with others--for free!

    We have seen results on paper coated with Ron's formula. We saw one beautiful print. Truly beautiful. Exquisite. So his formula definitely works. But when we were told by the person who made the print that he had to coat about 10 sheets of paper to get a perfect coating--and there was no guarantee that on that piece of paper the exposure and amount of dodging and burning would be perfect, we realized that making your own silver chloride emulsion was for those who truly enjoyed, and got their deepest pleasure from, working in the darkroom and who only made a few prints a year. It clearly was not for those whose primary concern is making photographs--lots of photographs, as Paula and I do.
     
  13. Photo Engineer

    Photo Engineer Subscriber

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    I think that some points need to be commented on or clarified.

    Michael did indeed consult with me and pay me for making a run of my emulsion and a set of prints for him. I did indeed tell him that the reciprocity failure, latent image keeping and raw stock keeping were untested with my emulsion at that time, and would need to be tested. That was about 2 years ago in the early stages of my work. I have now run those tests.

    I have not posted my formula in this thread. My formula is quite a bit simpler and quite different as noted earlier.

    The fact is that I am getting about 95% yield on my coatings, and the speed does vary with small batches, but this has no relationship to what could be done with the proper plant facilities. With a good coating machine and the proper scaling, my formula could be coated quite as easily as any other production emulsion formula.

    The advice I gave them was that there were several places that could make what they wanted, better than I could alone. I named facilities that might help them as far as I knew them. I warned them that a small machine run would not necessarily make possible a large scale run and that duplicating Azo paper would not be an easy task. It took me a year to get to the point I showed them nearly 2 years ago.

    I think that the scaling problem is being seen right now in the results that Michael has described of his sample coatings. It is similar to the growing pains that I have had over the 3 years making this emulsion in several locations.

    If you wish more information from an outside review, you might wish to re-read Alex Hawleys comments here in this forum.

    PE
     
  14. Donald Miller

    Donald Miller Member

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    Good point. I do know that Michael is pretty critical of what an Azo (like) emulsion should and would evidence. In fact I imagine that he would be the final determiner of those characteristics considering the breadth of the experience he has had with that particular material.
     
  15. Alex Hawley

    Alex Hawley Member

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    Hi Ryan,

    I posted three scans in this thread. I also posted Azo prints made from the same negatives on the same day that I was printing on the Mowrey paper. And for a third example, there's the original Azo scan of the Cola Sign in my gallery that I made nearly two years prior to the others.

    Of course, one can't make any accurate assessment of these prints from low jpegs on the internet. However, as I said before, Ron's emulsion works. Yes, it differs in some characteristics from Azo as I explain in the thread, but that is the nature of emulsion making. Its fully capable of very fine results.

    Cheers,
    Alex