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  1. #1

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    Gelatin coating paper by air spray

    I would like to improve my paper coating technique and start researching on the possibility to spray the emulsion with an hot air gun. In some old threads (and n other forums), I found that someone either used or, at least, experimented already with such technique. I would appreciate if some of the exports could elaborate on the topics and explain why essentially nobody is using it any more.

    Thanks,

    Mantinieri

    www.mantinieri.com

  2. #2
    dwross's Avatar
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    Hi Mantinieri,

    It sounds like it should be a really great idea, but it turns out not so much. If you are talking about silver gelatin emulsions (and not a plain gelatin subbing for another, non-gelatin based process), it's basically way more trouble than it's worth. Coating paper is very simple and straightforward. There are a few preparatory steps, and there are a couple of tools that make things easier, but nothing compared to setting up the precisely heated well and lines necessary to keep silver gelatin emulsion spraying out consistently. Also, spraying would very likely introduce small air bubbles into your coating.

    Regarding previous posts: it may be that you ran across the topic of 'air knife'. There are some good articles on the internet about that technology. It's used in some commercial emulsion coating operations, but it's an industrial scale solution that's probably not (and I never say 'certainly' about any technology) useful for our purposes.

    Good luck and fun. Hope to hear more from you.
    d

  3. #3
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    I have a friend that uses a spray gun for emulsions. He uses dilute unhardened emulsion and sprays on several layers to prevent running of the dilute emulsion. It can be done, but with great difficulty in terms of experimentation and then repeated applications. It is not recommended unless you wish to invest time and money into getting the best combination of variables that give you what you want.

    AFAIK, there are very few people doing this, and it has never found commercial application in photography.

    PE

  4. #4
    Hexavalent's Avatar
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    I've tried spray coating, but only for sizing and carbon-transfer 'glop'. Temperature, concentration, humidity, flow rate etc., are all significant variables. For the time and effort, I wouldn't recommend it unless you are prepared to invest a lot of time, effort and money into a rather finicky process.
    - Ian

  5. #5
    Ian Grant's Avatar
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    We used spray coated emulsions commercially for over 10 years, however it was quite specialist and also tricky, the emulsions had been designed for use that way. For a few months (early 80's) we trialled Ilfospeed Gd3 emulsion which worked equally as well once we found the right dilution.

    It also needs very good fume extraction and you need to wear goggles and an airline respirator otherwise it's hazardous.

    It's not the ideal way to coat paper or similar we were coating painted surfaces, as Dennise has said coating paper is relatively easy with less wasteful techniques.

    Ian

  6. #6

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    Some MAJOR industrial use has actually been known, but most of this was not for pictorial work.

  7. #7
    Photo Engineer's Avatar
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    Quote Originally Posted by Ray Rogers View Post
    Some MAJOR industrial use has actually been known, but most of this was not for pictorial work.
    Then please tell us about it!

    PE

  8. #8
    Ian Grant's Avatar
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    Johnsons of Hendon sold dried powdered photographic emulsion which was used industrially and I think often sprayed. The company still exists as Johnsons-Photopia but this side had nothing to do with the chemistry division which was closed in the 70's.

    Johnsons are the oldest Photographic company still trading, as well as being the first They supplied Fox Talbot.

    There was a degree of inter trading between Johnsons & Ilford, Johnsons made chemicals used and re-sold by Ilford, and Ilford sold some chemicals to Johnsons. I have some Ilford Amidol which has the Johnsons name on it, I've seen Johnsons chemicals with Ilford's name. The point being maybe the Johnsons Granulated Emulsion may well have been made by Ilford. (It's my Ulford Amidol shown on the site).

    I came across examples of emulsions being sprayed for specialist applications back in the 70's while doing research, but all written no visual examples or evidence.

    Ian

  9. #9
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    If dried emulsions were that "good" and if spraying were that useful, it would have been more widespread IMO. Today, we have liquid emulsions that go bad on store's shelves, but dried emulsions would presumably keep better. So, why not sell them once you are set up to dry them? I would think that there were hidden problems.

    I have been told that drying an emulsion and then working with it after reconstitution often resulted in problems with denaturing of gelatin and emulsion fog. IDK how prevalent this was but I know that EK and most other companies stayed away from it. In fact, Kodak had a whole line of industrial emulsions that were sold as liquids for coating. None were dried even though they had the capability. Ilford currently sells liquid emulsions and yet do not dry any.

    Maybe that is why Johnsons quit selling them, problems!

    I have seen some excellent examples of sprayed emulsion coatings, but they were very difficult to do, as I noted above.

    PE

  10. #10

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    Thanks to all the respondent. What drove my attention into the methodology is the following patent:

    http://www.patentstorm.us/patents/56...scription.html

    It gives very precise instructions and, apparently, there is not even the necessity to heat the lines.

    Mantinieri

    www.mantinieri.com

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