Ferric ammonium oxalate tests

Dichromated Gelatin.
Joe Farina
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Joined: Wed Jan 07, 2015 2:10 pm

Re: Ferric ammonium oxalate tests

Post by Joe Farina » Sat Jun 29, 2019 11:01 am

When the layer has a dense milkiness after processing, that suggests soft gelatin to me.

Unless you control temperature and humidity in your environment, those factors can (and do) change. So a reliable temperature/humidity gauge or meter is essential, preferably two or more, so that accuracy can be checked. The temperatures of processing solutions (water and alcohols) change unless controlled. (Of course, milkiness can also be caused by processing temps which are too high.)

For my MBDCG, I've found that a ~25 micron layer gives the best results.

I have experience with regular 457-exposed DCG and with MBDCG (red and green exposed). I would say that the most important factors are the hardness of the layer before exposure, and the processing method after exposure, including ageing/heating and fixer-like substances -- which cause additional hardening to exposed and unexposed areas. "Hardness" in a DCG layer always means two things, exposed areas and unexposed areas, and it helps to keep that it mind.

Holograms can't reconstruct through a layer of milk, though many times I wished they could :)

Martin
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Joined: Sat Apr 04, 2015 2:36 am

Re: Ferric ammonium oxalate tests

Post by Martin » Sun Jun 30, 2019 2:25 am

vasimv wrote:
Sat Jun 29, 2019 8:13 am
Failed again with same emulsion (non pre-hardened, 2g FAC/12g gelatin) and 2/3 layers of scotch tape as mold. Nothing holographic at all, i see only very bright colors (up to fully mirror coloured surface) with coins reflections in it but no depth.
Did I get it right, you mixed 12g gelatin with 2g FAC (in, I believe, 100ml water) to make the coating?

If so, this would be roughly 10x the quantity of FAC I put into my gelatin. Note also, by removing 1/6 of the total layer volume you'd expect a substantial wavelength shift (by say, ~60nm, which would put your reconstruction wavelength around 340nm).

vasimv
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Joined: Tue Apr 23, 2019 2:16 am

Re: Ferric ammonium oxalate tests

Post by vasimv » Sun Jun 30, 2019 8:40 am

Martin wrote:
Sun Jun 30, 2019 2:25 am
Did I get it right, you mixed 12g gelatin with 2g FAC (in, I believe, 100ml water) to make the coating?

If so, this would be roughly 10x the quantity of FAC I put into my gelatin. Note also, by removing 1/6 of the total layer volume you'd expect a substantial wavelength shift (by say, ~60nm, which would put your reconstruction wavelength around 340nm).
I'm really confused now. :) That is about same amount described for your FAO tests (30g gelatin + 6g FAO + 300ml water).

Anyway, going to return to dipping method, seems my method of mixing FAC+Potassium alum with gelatin makes something do wrong (may be distribution of FAC isn't uniform, kind of "clustering" or something like that prevents getting holograms in that way). I'll try to sensitize+harden emulsion at same time with just one mix FAC+Potassium Alum solution to simplify things.

vasimv
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Joined: Tue Apr 23, 2019 2:16 am

Re: Ferric ammonium oxalate tests

Post by vasimv » Sun Jun 30, 2019 12:06 pm

Joe Farina wrote:
Sat Jun 29, 2019 11:01 am
When the layer has a dense milkiness after processing, that suggests soft gelatin to me.
I use 250 bloom "Pure Beef Gelatin Powder". Ordered also 300 bloom "SuperClear Gelatin", may be it'll do better. I get a lot of milkyness when undexposure also. Seems FEG emulsion has its own "features".
Joe Farina wrote:
Sat Jun 29, 2019 11:01 am
Unless you control temperature and humidity in your environment, those factors can (and do) change. So a reliable temperature/humidity gauge or meter is essential, preferably two or more, so that accuracy can be checked. The temperatures of processing solutions (water and alcohols) change unless controlled. (Of course, milkiness can also be caused by processing temps which are too high.)
Yeah, did install humidity/temperature sensor in the room but seems the DHT-22 sensor is a bit broken, reports too low humidity (always below 75%), have to replace iit.

Martin
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Joined: Sat Apr 04, 2015 2:36 am

Re: Ferric ammonium oxalate tests

Post by Martin » Sun Jun 30, 2019 12:42 pm

vasimv wrote:
Sun Jun 30, 2019 8:40 am
Martin wrote:
Sun Jun 30, 2019 2:25 am
Did I get it right, you mixed 12g gelatin with 2g FAC (in, I believe, 100ml water) to make the coating?

If so, this would be roughly 10x the quantity of FAC I put into my gelatin. Note also, by removing 1/6 of the total layer volume you'd expect a substantial wavelength shift (by say, ~60nm, which would put your reconstruction wavelength around 340nm).
I'm really confused now. :) That is about same amount described for your FAO tests (30g gelatin + 6g FAO + 300ml water).
I think, the only time I used such high amounts of FAO or FAC was related to 532nm exposures. But it never worked.
I guess the thing you're alluding to was Dinesh's post here: https://holographyforum.org/forum/viewt ... ?f=7&t=440
Here's the first set of tests. Plates were made as follows:
30 gms 250 bloom pork gelatin
6 gms FAO
300 mls water
That was somewhat special since Dinesh did expose his plates at 457nm.

Joe Farina
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Joined: Wed Jan 07, 2015 2:10 pm

Re: Ferric ammonium oxalate tests

Post by Joe Farina » Sun Jun 30, 2019 2:19 pm

vasimv wrote:
Sun Jun 30, 2019 12:06 pm
I get a lot of milkyness when undexposure also.
Maybe part of the problem is underexposure, which of course can cause milkiness. On the other hand, I don't understand the ferric mechanism when compared to DCG. I would guess that differential hardening in the layer occurs at some point in the process, because soft gelatin encourages void formation, and hard gelatin discourages it. The high DE described by Dinesh (comparable to DCG) and the alcohol dehydration suggest air void formation to me.

On page 2 of the linked thread provided by Martin, it shows the Wizard hologram made by Dinesh. I would guess that Dinesh's laser was doing around 200mW at 457 (Some Melles-Griot lasers like the one I used, and possibly Dinesh's, are dual-beam lasers putting out a nominal 200mW per beam).

He said that, with his setup, a 4 minute exposure corresponded to 120mJ. The Wizard was a 25 minute exposure, so we're talking some pretty high numbers. Dinesh estimated the ferric system to be about 10 times less sensitive for a reflection holo, compared to DCG, which sounds like a conservative estimate to me.

Of course, you're using a different ferric compound and a 405nm laser, so that could change things.

Just to clarify: when I said "soft gelatin" earlier, I didn't have in mind bloom strength. When I saw milkiness in my MBDCG (which was very often), I believed that the gelatin was too soft (for whatever reason) during one or more points in the process as a whole. I saw a big improvement when a hardening agent was added (very sparingly) to the emulsion before coating.

Martin
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Re: Ferric ammonium oxalate tests

Post by Martin » Mon Jul 01, 2019 2:05 am

Joe Farina wrote:
Sun Jun 30, 2019 2:19 pm

The high DE described by Dinesh (comparable to DCG) and the alcohol dehydration suggest air void formation to me.
Agreed.
He said that, with his setup, a 4 minute exposure corresponded to 120mJ. The Wizard was a 25 minute exposure, so we're talking some pretty high numbers. Dinesh estimated the ferric system to be about 10 times less sensitive for a reflection holo, compared to DCG, which sounds like a conservative estimate to me.
Yes, absolutely. That's why I was deeply frustrated. The data provided by Dinesh didn't even remotely resemble anything Ahmet & I had measured in my lab back then. It's been really disappointing. Even more so, as Dinesh did his tests on the very same type of gelatin.

The whole thing has been a great mystery to me - until this year when I learned about the notorious "unreliability" of FAC (and, I assume FAO as well). This has been mentioned in Mike Ware's article (https://www.mikeware.co.uk/downloads/SimpleCyan.pdf). He there avoids commercially available FAC - and advocates for its in situ generation (mixing ferric nitrate + citric acid + ammonia) instead.

Moreover, you're right, Joe, there's also the wavelength issue. 457nm may be quite a different ball game than 405nm.

When I started my experiments with ferric gelatin, I equally run tests with DCG materials (ammonium dichromate, potassium dichromate and potassium chromate that is) under exactly the same recording conditions - at 405nm. It turned out FEG was at least on par with DCG. Occasionally it would be even considerably faster. It's safe to say that FEG gives you more options in regard to processing. In that respect it resembles more AgX than DCG. For example, the processing allows for extremely broadband holograms (at least 400 - 660nm, possibly from UV-A into the near IR)

vasimv
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Joined: Tue Apr 23, 2019 2:16 am

Re: Ferric ammonium oxalate tests

Post by vasimv » Mon Jul 01, 2019 11:34 am

Joe Farina wrote:
Sun Jun 30, 2019 2:19 pm
Maybe part of the problem is underexposure, which of course can cause milkiness. On the other hand, I don't understand the ferric mechanism when compared to DCG. I would guess that differential hardening in the layer occurs at some point in the process, because soft gelatin encourages void formation, and hard gelatin discourages it. The high DE described by Dinesh (comparable to DCG) and the alcohol dehydration suggest air void formation to me.
Yes, i think so. No exposure -> no Fe(2) -> no crosslinking in H2O2 developer -> water dissolves gelatin and forms voids. That is why i'm playing with potassium alum - to fix whole layer and prevent forming these void gaps. I'd want to get fringes with H2O2-crosslinked and SO4-hardened gelatin, without gaps. To fully simulate DCG's behavior, where as i understand - fringes gets formed between gelatin hardened by laser exposure and hardened during light flooding after exposure. That way i'd want to get fully hardened layer without gaps, strong enough to survive warm water bath, do less blue-shift when ferric salt gets washed out and/or be reprocessed again if needed.
Joe Farina wrote:
Sun Jun 30, 2019 2:19 pm
On page 2 of the linked thread provided by Martin, it shows the Wizard hologram made by Dinesh. I would guess that Dinesh's laser was doing around 200mW at 457 (Some Melles-Griot lasers like the one I used, and possibly Dinesh's, are dual-beam lasers putting out a nominal 200mW per beam).

He said that, with his setup, a 4 minute exposure corresponded to 120mJ. The Wizard was a 25 minute exposure, so we're talking some pretty high numbers. Dinesh estimated the ferric system to be about 10 times less sensitive for a reflection holo, compared to DCG, which sounds like a conservative estimate to me.

Of course, you're using a different ferric compound and a 405nm laser, so that could change things.
Yes, FEG''s sensitivity is a bit confusing question but not real issue for me at this moment as i'm playing with small slides now. I'd want to get stable holograms first. :)
Martin wrote:
Sun Jun 30, 2019 12:42 pm
vasimv wrote:
Sun Jun 30, 2019 8:40 am
I'm really confused now. :) That is about same amount described for your FAO tests (30g gelatin + 6g FAO + 300ml water).
I think, the only time I used such high amounts of FAO or FAC was related to 532nm exposures. But it never worked.
Ugh, ok. I'll try to decrease FAC concetration up to ten times. But wouldn't that really decrease sensitivity? I do exposures up to 15-30 minutes with my low powered laser diodes (few milliwats i think) already, more will be very inconvenient...

Btw, how do you mix FAC and gelatin? It looks like i'm missing some important point here as results are very unpredictable, even with same recipes. Usually i do dissolve FAC in 10 ml water and then add to dissolved gelatin. May be it'll be good idea to just dissolve gelatin in FAC solution, to be sure it'll get distributed uniformly?

Martin
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Joined: Sat Apr 04, 2015 2:36 am

Re: Ferric ammonium oxalate tests

Post by Martin » Tue Jul 02, 2019 3:40 am

vasimv wrote:
Mon Jul 01, 2019 11:34 am
I'll try to decrease FAC concetration up to ten times. But wouldn't that really decrease sensitivity?
Yes, that's possible.
The way I see it now is that speed of FEG essentially depends on the kind of gelatin AND the integrity of FAC. Both are equally important.
I had success with only two brands of gelatin, my standard food grade gelatin (acid treated, pork skin) and an "inert" photo gelatin (bovine skin, type B) from Gelita. Since I wanted to keep the photo gelatin for AgX work, I stayed with the culinary gelatin. Ahmet and I had tested many brands and types of gelatin. None did perform at the level of my food grade gelatin.
I do exposures up to 15-30 minutes with my low powered laser diodes (few milliwats i think) already, more will be very inconvenient...
You might shorten your exposure times by exposing a much smaller area (say, 1-2cm).
Btw, how do you mix FAC and gelatin? It looks like i'm missing some important point here as results are very unpredictable, even with same recipes. Usually i do dissolve FAC in 10 ml water and then add to dissolved gelatin. May be it'll be good idea to just dissolve gelatin in FAC solution, to be sure it'll get distributed uniformly?
In order to avoid mold, I keep a stock of 10% gelatin gel and a10% FAC solution in a a fridge. To prepare my coating solution, I take out some gelatin gel and put it into a microwave oven for a few seconds until it becomes liquid. Under safelight I pour a few drops of FAC into the gelatin solution and make the coating.

vasimv
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Joined: Tue Apr 23, 2019 2:16 am

Re: Ferric ammonium oxalate tests

Post by vasimv » Wed Jul 03, 2019 9:36 am

Couldn't repeat success with dipping method. I've tried dipping in 4% FAC + 1% Potassium alum solution and previous method with Potassium Alum + water + 4% and 1% FAC solutions. All of them gave bad results, i see some small holographic spots with depth or big but very faint holograms, mostly with a lot of milkyness and reflective color surface (almost like mirror). Not sure what is wrong, could be increased vibrations (neighboors AC and water pumps units seems working more actively as overall air temperature have raised 1-2 degree lately) or my bad processing.

Sensitivity at lower concetration of FAC decreased a lot, slides dipped in 1% FAC solution gave 4-6 times less sensitivity than with 4%. And more milkyness it seems, although it could be just underexposure.

Update: did one more batch with fixer+water+4% FAC dipping. Almost same results - weak hologram on whole slide or bright but small holographic spot at corner. It looks like i can't find right exposure and overexposing it is very easy. Environment's humidity got changed lately (less than 80%) and i think i did underexpose most of the batch just. Guess i need experiments in more controllable environment. :(

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