preparation of photosensitive coatings for Lippmann photogra

This is a forum exploring Lippmann photography.
Martin

preparation of photosensitive coatings for Lippmann photogra

Post by Martin »

Hans wrote:That begs the question: How thick is an index matching layer? From experience I know that when mold coating a 10x15cm plate with 60um spacers about 5ml of liquid gelatin is needed. But when index matching only a small drop of liquid is needed. How many ml is a small drop? Perhaps we are talking a fraction of a um with index matching. Has anyone ever tried it?
That's an interesting subject.
I tend to agree that the index matching layer is likely to be extremely thin (most definitely well below 1um). So far this would favor the method involving a reflector.
However, one thing we didn't mention yet is the problem of dust particles. If you've dust particles within that index matching layer (and I assume this is a very serious issue), you'll easily get greatly increased distances between the recording layer and the reflector – at least locally.
Sergio

preparation of photosensitive coatings for Lippmann photogra

Post by Sergio »

Besides the serious dust problem, the index matching itself is also dramatic due irregular space, as Denisyuk demonstrate in your 1962 Soviet papers I agree with Martin about this distance, ideally one could use liquid metal or use water plus detergent index matching BUT with a vapour permeable film base to allow the water evaporate and make the gelatin - mirror reunion. :D
walschuler

preparation of photosensitive coatings for Lippmann photogra

Post by walschuler »

1) To my knowledge Darran Green is the current leader in home preparing Lippmann emulsions from scratch, and making images too. But also see the "ultimate" website of Yves Gentet, who is in France. He makes great holographic emulsions, and was offering Lippmann emulsions which have the same grain structure, but are thinner than the holographic ones (see below), though they are not advertised at present.

2) There are tradeoffs to be made in this game: for simplicity use no reflector, emulsion facing away from the camera lens, as stated in a post above. But then the reflected wave is only about 4% as bright as the incoming wave, and so the interference fringe contrast is cut severely. The result is an image of lower contrast and saturation. That having been said Darran's results and Hans Bjelkhagen's results, at their best are about 80-85% as good as Lippmann's or Neuhauss's from the early 1900s. In part this has to do with careful processing post exposure.

3) Coherence length is a major issue for at least 2 reasons. First, the greater the coherence length the deeper the interference pattern. The deeper the pattern the more layers, and in general the stronger the resulting reflection and image. Secondly, if the reflector you use is farther than the coherence length from the emulsion, due to an air gap or index-matching layer thickness, then no pattern will record in the emulsion, and you will merely get a black and white negative with no color.

Coherence length is given (to a good approximation) by: c.l. = (λ)^2/Δλ = (wavelength squared)/(bandwidth) in consistent length units. Two examples: for the visible spectrum, take the wavelength as 5500 angstroms (550 nanometers) and the bandwidth as from 3500 up to 6500 angstroms= 3000 angstroms. The coherence length is then about 10^-4 cm, or 1 micron. Hence, as stated above, for white or general broadband light an emulsion deeper than about 1-1.5 microns is not needed, and in fact to the extent that photons not in the interference pattern expose the emulsion at greater depths, they constitute noise and decrease the quality of the image. Thus the usual holographic emulsions, which are typically 6-7 microns thick, are not ideal for Lippmanns. A second example, for a typical gas discharge spectrum line the linewidth becomes the bandwidth, and these vary quite a bit, but take the line to be 1 angstrom wide. From the equation above you can see that the coherence length will be about 3000 times longer than in the first example, which was 10^-4cm = 10^-3mm, so the 1 angstrom line will have a coherence length of about 3 mm.

4) In my experiments, using aluminized mylar film of an ordinary sort as a mirror, adhered to Agfa 8E-75 with
with various evaporants, and using as a light source a sodium vapor safelight, which has the 2 bright, fat (several angstroms wide) yellow D lines at about 5900 angstroms, I could see that not only did I get color, but I got a 3-D image of the bumps and crimps in the mylar film, which had occurred due to uneven handling and adherence. I recorded a very shallow Lippmann reflection hologram! A 1 mm deep hologram is not very pleasing for ordinary 3-D, but using a non-laser to make an even quite shallow hologram has interesting possibilities. Without the mylar and using the sodium vapor lamp for illumination of objects in a darkened room you still get quite strong color because the fringe pattern is still quite deep, and it gives interesting images. You also see that a single color source may result in multi-colored images, in a not easily controlled way, due to variations in density (i.e., exposure) in the negative.

It should also be noted, from the equation above that longer wavelengths have longer coherence lengths, as noted in a post above, so you get deeper patterns in the red than in the blue. Further, the interference layers are thinner (λ/2 spacing!) in the blue so that the required resolution of the emulsion is set by the blue if you are doing broad band work and it is the shortest wavelength.

5) I have used Kodak D-19 as a developer, with only modest success; better is one of the older formulas, especially one by the Lumiere brothers, which has storable parts A and B which are mixed at time of use.
Lippmann and others succeeded with many types of developers, tanning and non-tanning, and with both unbleached and bleached (usually mercury based) images. Generally these images are not fixed,as fixing tends to shift the color to shorter wavelengths due to emulsion shrinkage. I also found that bleaching shifted the color of narrow band images, using ferric EDTA bleach as for holograms. For wide band images bleaching tended to destroy the images.

6) Besides a narrow band source such as the sodium safelight, an excellent early trial subject is a spectrum. It is relatively easy because since the colors are spread out, at each point along the spectrum in effect you have only a narrow band width, which means, as above, that the coherence length is deeper than if you had the whole visible spectrum at each location in the image. This will also show you, by way of the intensity variation along the spectrum, just how panchromatic the emulsion sensitivity is. By the way, Lippmann showed, first using Fourier synthesis theory and then in practice, in contrast to his doubters, that he could record a good white color. In that case the interference patterns add up to one thick layer, with a density (intensity) maximum 1/4 wavelength in from or at the surface of the emulsion, depending on whether there was a mirror in perfect contact or just the air interface.

7) You really should look at the Wiki when it comes back up.

8)Finally, where are you Layladies from and who are you?

I hope this all helps, and I am Yours,

Bill Alschuler
San Francisco
walschuler

preparation of photosensitive coatings for Lippmann photogra

Post by walschuler »

Dear Laywomen,

One further note. In the post above I discuss how coherence length is an issue. For broad band work therefore if you use a mirror film as the reflector you need to get one on which the mirror coating is naked. This takes some inquiries as most on the market have some sort of protective coat on both sides. You want a film that is only protected on one side, and apply the unprotected surface to the emulsion. For narrow band work it is not an issue.

Bill Alschuler
walschuler

preparation of photosensitive coatings for Lippmann photogra

Post by walschuler »

Another note to add to my long post above:

I have used a low pressure sodium vapor lamp, found in my school's darkrooms as a safelight. I have the specs somewhere, but I think it was about 150 watts. Eventually I bought my own tube and built a diffuser box and used it first to create a field of pure color, just aiming at the diffuser, and then used it to illuminate objects in a darkened room. I photographed using a 4x5 Speed Graphic with old plate holders or film holders. All this was in aid of my Lippmann research. I started with Agfa 8E-75, then tried a range of other films and plates. Currently I use Slavich PFG-3C (panchromatic) film and plates for the most part. Yves Gentet's products are on my list to try in the near future.
Jeffrey Weil

preparation of photosensitive coatings for Lippmann photogra

Post by Jeffrey Weil »

Hello Everyone,

I'm not a lippman guy so I might be totally off base on this one but I do have an idea. How about metalizing the film itself and then removing that metal before processing.

You could use a silver nitrate solution or electroless nickel. Both can be applied at room pressure with some simple spray equipment thats easily available.

To remove the silver coating you would use a dicro acid solution. If the film has not been processed yet I don't think it would mess with the latent image. If nickel is used that has its own solvent, once again I don't think it would mess with the emulsion.

Has anyone tried this? It would be true intimate contact with the emulsion. No gap at all. Pretty good reflectivity.

Jeffrey Weil
NorthBeach Holography Inc.
Martin

preparation of photosensitive coatings for Lippmann photogra

Post by Martin »

Jeffrey Weil wrote:Hello Everyone,

I'm not a lippman guy so I might be totally off base on this one but I do have an idea. How about metalizing the film itself and then removing that metal before processing.

You could use a silver nitrate solution or electroless nickel. Both can be applied at room pressure with some simple spray equipment thats easily available.

To remove the silver coating you would use a dicro acid solution. If the film has not been processed yet I don't think it would mess with the latent image. If nickel is used that has its own solvent, once again I don't think it would mess with the emulsion.

Has anyone tried this? It would be true intimate contact with the emulsion. No gap at all. Pretty good reflectivity.

Jeffrey Weil
NorthBeach Holography Inc.
That's interesting. I've never heard of nickel in that context. However, I am fairly sure silvering has been done previously (I think Ives did this) – not through spraying though.
After the photographic exposure, how would you get rid of the nickel again? What solvent would you have to use?
Jeffrey Weil

preparation of photosensitive coatings for Lippmann photogra

Post by Jeffrey Weil »

Hey Everyone,

The nickel has it own "cleaner" that comes with the kit. The silver solvent you mix up your self, nickel is another jug you buy with the main chemistry.

The other way to silver is with a vac chamber.

Jeffrey Weil
NorthBeach Holography Inc.
Danny Bee

preparation of photosensitive coatings for Lippmann photogra

Post by Danny Bee »

I know this is probly been thought of before but what about coating a front s mirror? or use a front s mirror index to the plate?
Jeffrey Weil

preparation of photosensitive coatings for Lippmann photogra

Post by Jeffrey Weil »

Hey Danny,

I think that would work but Lippmann folk want to remove the emulsion from the mirror and replace it with a wedge or whatever. Coating a mirror would make that pretty hard if not impossible.

Once again, this is just a guess. I don't do lippmanns.

Jeffrey Weil
NorthBeach Holography Inc.
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