Getting the Silver out.

[Joe Farina]

This gelatin layer won't come off even if boiled

Wow, that sounds pretty wild. Is that what happens when gelatin gets old and hard?

John, I'm looking forward to hearing about your experiment of sensitizing a silver halide emulsion with dichromate. I'm fairly certain that Danny was referring to some Bulgarian work done in the early 1980's (Mazakova et al.) and published in Optical and Quantum Electronics, Volume 14, (1982), part 1 on pages 311-315. Part 2 on pages 317-320 is by the same authors, and is related to Part 1, but is on essentially another subject. If you get into it in the future, and want this paper, I can email it to you.

I studied these papers years ago, and they are quite interesting, but as I recall, there was something preventing me from looking into it any further, because of something that I read in one or both papers (but I don't remember what it was).

[JohnFP]

Joe, if it has anything to do with silver and DCG in an emulsion, then I would love to read them. Thank you.

I have been thinking about this, yes, my mind is one track holography lately. If I have silver and DCG in the film then I will surely need to be very careful with safe lighting. Or do I? :think:

I may try to sensitize one in the dark and keep it light free till fixing and possibly even silver develop it prior to fixing and I may try one to sensitize and keep it with DCG lighting till fixing (this will be considerable time as sensitizing, drying, settling and exposing will all be done with bug lights, 1/2 hour?).

[Joe Farina]

John, I emailed the paper. Yes, they combined silver halide and dichromate in a single layer. I don't know about the safelight. I get the impression that safelighting was used for the entire process until exposure, but I'm not sure. See page 312: "....the dried layer is exposed to light...."

One thing which came to mind, and which is mentioned in the paper, is that silver halide materials typically scatter blue light. That's the nice thing about DCG as opposed to silver, scattering isn't much of a problem since the DCG emulsion is grainless. The authors point out that (p. 321): "The silver halide crystals must be superfine and in a quantity such as not to deteriorate by scattering the contrast of the recorded interference pattern...."

They did not use commercial plates. They used a diffusion method to get a low concentration of superfine silver halide grains, then they dipped the emulsion in a bath of dichromate (with dye added for the silver halide). Since they added dye, it looks like the action of exposing the virgin silver halide grains is important, so that's why it looks like safelighting is needed.

The fact that the plates will probably be loaded with a heavy amount of silver halide is in contrast to what the authors specify, so that's something to keep in mind. Maybe there could be a way to remove "some" of the silver halide from the emulsion, if that becomes necessary (maybe a "weak" fixer?). Also note the importance they attach to "superfine" grains. I assume the emulsion in question has grains that qualify as superfine. As an added precaution, you might want to expose at a longer blue wavelength, i.e., 488nm, to reduce the effects of scattering, or maybe 514nm if you are more comfortable with that.

Good luck.

[JohnFP]

Thanks Joe, can't wait to read and digest it. Interesting points you point out.

[Martin]

[I studied these papers years ago, and they are quite interesting, but as I recall, there was something preventing me from looking into it any further, because of something that I read in one or both papers (but I don't remember what it was).

I assume it was the relatively moderate (50%) DE this method did produce according to the authors.

I think I already mentioned this: the Mazakova approach seems to be at least inspired by an old patent, Seymour US 1984090, Photographic material for making colored prints).

Seymour points out:

I have found a simple method by which a bichromated gelatin layer may be optically sensitized to the longer wavelengths and at the same time contain a suitable deye for a color print. (...)
My invention is carried out by adding to a bichromated gelatin a quantity of silver iodide having a dye adsorbed to it. In practice the same result may be attained by coating a support with an emulsion containing the dyed silver idodide and then sensitizing this emulsion by bathing in bichromate.

[JohnFP]

First I want to point out that they state that some of the Cr goes directly to CrIII and skips the CrV. But they also state that the process of Cr reduction to CrIII is not fully understood yet. The paper was done in '81, so I would take that with a grain of salt (silver salt).

Seems scatter may really be a problem so I will surely shoot in the Green (514) to try to minimize that. Also, I am not too worried about the loss in sensitivity as more silver is in the emulsion, I am not after that. I am after the ease of fabrication DCG film. How nice to soak a plate and be able to shoot in in 15 minutes or so. Whereas it took a couple of hours to make with a minumum set time of 4 hours and it only lasted a day or two.

Something else I would like to try is to get the film hardeness down, possibly using an alkaline solution of AmDi to sensitize.

Also, when I was doing my research on Gelatin types, I found that Bone (not Bovine) gelatin has a small amount of Silver already naturally occuring in it from the Bones. I always stayed away from Bone gelatin for that reason. Now I wish I had done some testing with that stuff too.

Anyway pretty excited about getting into the lab. Columbus day is one of those few rare days I have off but the kids and wife have school and work. A full day in the lab may be coming.

Who makes their own Silver and what is the best way to make the grains smaller? I remember reading about it in someones post but havent been able to find it yet.

[holo_cyware]

In our case since the plates are pancromatic - silver bromide being the main silver constituent - maybe it can be rehalogenated with a bleach containing potassium iodide, after an exposure to light in order to get rid of the bromine. An alcohol/iodine solution may work better. As about the sensitizing dye, it can be added in a later bath.

Anyway, since iodine is less chemically active then bromine a simple "subtitution" won't work here, and I highly suspect that even silver bromide may have a cathalitic efect for reducing the AmDi.

[JohnFP]

Ok, thanks. I will keep that in mind.

[JohnFP]

Seems like a long wash time under running water, but maybe there's a reason. Don't know why he had to dry them before going into the sensitizing bath (probably that's why he used the Photo-Flo).

Joe, I bet the long wash time is to insure there is no fixer left in the emulsion. AmDi would not like that so much.

As for the drying, I have no idea. Ima not going to dry my first try. Going to go straight from fixer, to wash to AmDi sensitizing. Remember, I am looking for the simplest, easiest and quickest method to make a plate. If I can do this, I am sure I will spend much more time in the lab actually making holograms.

Also, I remember someone (holo_cyware?) mentioning that he was going to try to get some of those plain gelatin coated plates (gosh, I just can't find the thread). I mentioned they never go back to me, but I had a brain fart. I was asking them for some samples to try and if they worked good I would buy some and post my findings on this forum. It is about the samples they never got back to me on, not purchasing some. Sorry I mislead you all.