Gelatin coating paper by air spray

[Mantinieri]

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

 

[dwross]

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

 

[Photo Engineer]

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

 

[Hexavalent]

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 Grant]

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

 

[Ray Rogers]

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

 

[Photo Engineer]

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

Then please tell us about it!

PE

 

[Ian Grant]

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

 

[Photo Engineer]

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

 

[Mantinieri]

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

http://www.patentstorm.us/patents/5683717/description.html

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

Mantinieri

www.mantinieri.com

 

[t-royce]

A visit to the Google Patent search on this provides three other related patents:

http://www.google.com/patents?q=5683717&btnG=Search+Patents

 

[Ian Grant]

There have been specific Patents for spraying photographic emulsions, I have some references back in the UK. Unfortunately searching the UK system online is almost impossible.

Ian

 

[dwross]

I kinda figured your idea came from a source like this. What's important to remember is that a silver gelatin photographic emulsion isn't just silver suspended in gelatin. The second a solution of silver nitrate hits a solution of gelatin and bromide or chloride salt, the fundamental nature of the solution changes. Think the difference between vegetable oil and mayonnaise. The solution in the patent, with its plasticizers and 'surface active agents', including lecithin, held at a very high (for most emulsions) temperature, is different enough from a silver gelatin photographic emulsion as to make any comparison essentially meaningless.

 

[Photo Engineer]

I agree totally with what Denise has posted. I would like to add that some of this work cited uses fish gelatins which are totally different than pig or bovine gelatins. Among other things, fish gelatins do not chill set and must have other ingredients added to allow them to solidify, or the water must be removed.

PE

 

[Ian Grant]

Back in the 70's I photocopied a section from a book on emulsion coating, there was a short piece on spray coating, I think it was possibly E.J.Wall. I came across the pages again this Easter, I should be able to find them when I'm back in the UK later this month, along with the Patent references.

Ian

 

[Ray Rogers]

Then please tell us about it!

PE

?

They have been used for example by Lockheed Martin (sort of... companies merge and change names...) They had 30 x 30 ft “camera” room cameras where oversized materials were exposed. The lens was set in the wall between the "camera obscura" and the "stage" room where the original was located and illuminated.

These rooms served the dual purpose of both camera and enlarger; once the negative was ready, the process was reversed and light forced through the negative was sent through the lens and onto large metal sheets or Masonite boards sensitized with their own liquid photographic emulsion. I am pretty sure these were sprayed on, (I could look at the pictures again) but I am sure the emulsion itself could also be applied by other methods; in fact, later on, for smaller scale work, it was.

Ray

 

[Ian Grant]

Emulsions where sprayed for engineering uses, often a photographic template was enlarged on to metals before cutting, the technique was called photo-lofting. One reason why dried powder emulsions were used was they had good long term storage without refrigeration. Any additional base fog was irrelevant.

Ian

 

[Photo Engineer]

Ray;

Do you have a reference?

Kodak had such a setup but it used standard coated materials cut to size for the job as follows:

Full Darkroom | Camera | Studo and Darkroom

The film was inserted on the left and exposed and processed in that room. The film was then reinserted in the camera which then projected the scene back into the studio onto paper which was then processed. I spent some time in this pair of rooms being given a complete tutorial on its use by the designers. It was located in Kodak Office and is now long gone.

PE

 

[Ray Rogers]

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.

May I Speculate?

Every coating method has (or should have!) its strong point.
Unfortunately, they also have their own weak points.

Spraying was good because it was a simple, manual method that could be used to make good coatings on large surfaces using equimpment and skill sets that already existed, while other methods were not, could not or did not.

The assumption that nobody is using it any more might be slightly anemic.
Both I and PE know people who use it successffuly to make good coatings...
Ian has used it, and well there must be others out there....

Perhaps a better question would be:

For what might spray coating be considered the method of choice?

 

[Ian Grant]

Perhaps a better question would be:

For what might spray coating be considered the method of choice?

An object that can't be laid flat, or a 3D object.

Ian

 

[Ray Rogers]

Emulsions where sprayed for engineering uses, often a photographic template was enlarged on to metals before cutting, the technique was called photo-lofting.
Ian

Yes.

PE, I have some material and referances here on "photo-lofting" too.
Ian, I wonder if that term is perhaps a bit more British than American?

 

[Photo Engineer]

Ian is exactly correct. That is about the only application for spraying on emulsions. But, even with non-flat surfaces, I have seen emulsions painted on with a brush. OTOH, with 3D or non-flat surfaces, DOF becomes a critical problem when exposing, depending on the method of exposure.

PE

 

[Ian Grant]

Lofting is the transference of engineering drawings to the materials to cut. It's a nautical and aeronautical term. Photo-lofting was used in the aircraft industry, what the US term was is any-ones guess.

Ian

 

[Photo Engineer]

Our oldest grandson works for a company here that does just that. They "draw" an image on metal and cut it. The front of the building sports a huge sculpture in steel that is quite famous.

However, digital means are now used. The image is drawn on a screen and then a program runs a laser or water cutter to carve out the image on the steel plates.

The photographic method is no longer in use for macro items, however, it is in use for making some microchips though.

PE

 

[John Shriver]

I'd say all microchip production is still based on photo-lithography. The experiments in electron beam exposure of the photo-resist just didn't succeed.

Now, they are currently using liquid immersion of the lens and chip to get the small feature sizes they need. But it's still optical. Best lenses Nikon and Zeiss can make.