Ferric ammonium oxalate tests

Dichromated Gelatin.
vasimv
Posts: 47
Joined: Tue Apr 23, 2019 2:16 am

Re: Ferric ammonium oxalate tests

Post by vasimv » Sat Jul 13, 2019 1:57 pm

Still can't figure out what's wrong with my dipping method, just getting weak spots with reflective and transmission holograms but can't repeat. Well, at least found out that my 405nm "ndv4313" diode has few centimeters coherence at 60ma and 120ma (latter should be 50mw or so) - got spot on transmission hologram with at least two centimeters depth distance.

I think, may be dipping emulsion in potassium alum creates unpredictable results because fixer restricts water and solutions from getting deep into layer, so it messes with developing and swelling bathes?

Joe Farina
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Re: Ferric ammonium oxalate tests

Post by Joe Farina » Sat Jul 13, 2019 5:49 pm

I would like to see a brief summary of your emulsion preparation technique (including type and quantity of materials used). I know this has been described before, but I would like to see it again, to help clarify things.

Personally, I don't like anything involving dipping, during emulsion preparation. It suggests non-uniformity of results. I've had good results incorporating all emulsion components prior to coating.

I can only guess about the necessity of pre-hardening the gelatin (in my case, with MBDCG, this was done with a small amount of chrome alum). I would personally opt to do this in the liquid emulsion (prior to coating). With regular blue exposed DCG, I only had good results when the coated plates (with the ammonium dichromate/gelatin mixture) aged for a certain period of time, to obtain some bias hardness as a whole. I have a feeling that a plain ferric compound/gelatin emulsion would likewise need some bias hardening. I don't know how this material ages (if it dark-reacts at all like DCG). The dark reaction was definitely helpful to me with regular DCG to get some bias hardness. So I would take a closer look at the hardening issue, and if your current hardening agent isn't working (are you sure about the potassium alum?), then I would look for another.

You've mentioned relative humidity numbers in the 75 to 80% range. These are huge numbers. They may affect the speed of the FAC system (DCG and MBDCG are most sensitive in warm and moist environments). But personally, I wouldn't want to do the processing in such a damp environment, especially if it's fluctuating. In my area, humidity is usually high in the morning, then drops way down in the afternoon. Also, DCG will absorb moisture from the air over 80% and vanish. In the DCG literature, processing in a stable and reasonably low-humidity environment has been recommended. I would think that up to maybe 70% might work (60% and even 50% or lower would likely be better). In my opinion, 75% would be pushing it, and 80% is definitely too high. The stability of the humidity is very important, if you're trying to get consistent results during either exposure or processing. Separating the exposure (high RH) from the processing (low RH) would be fine. But one needs to get a handle on what the RH and temperature are doing first, take the necessary steps, then document them for each exposure and processing session.

Yes, it is tedious at first, but if you're serious about getting improvements, then I think it's essential.

It's good your 405nm laser has some coherence. I think some people have had a lot of frustration by finding a 405nm diode that happens to work, frying it by applying too much current, etc., then being unable to find another one which had decent coherence length. If you want to make visible reflection holograms, you could try to make it as broadband as possible, as Martin suggested earlier. I personally don't have much experience with that, but in the wiki section it shows the very broadband Angel hologram made by John Pecora, and he used a plain water soak at the beginning of the process (this is described somewhere in the wiki). So that might be worth looking into. For narrow-band red-shifting, I think the hydrolyzed collagen would be promising, since a fairly long red-shift might be possible with long soak times (a spinner could probably be used to remove the collagen uniformly from the layer).

vasimv
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Re: Ferric ammonium oxalate tests

Post by vasimv » Sat Jul 13, 2019 9:15 pm

Joe Farina wrote:
Sat Jul 13, 2019 5:49 pm
I would like to see a brief summary of your emulsion preparation technique (including type and quantity of materials used). I know this has been described before, but I would like to see it again, to help clarify things.
If don't count alchemy experiments, i've tried (with 11..12g 250 bloom gelatin per 100ml water):

1. 1% FAC emulsion with veil coating
2. 2% FAC emulsion with veil and mold coating
3. 2% FAC + 0.5% potassium alum emulsion (it had very high viscosity, didn't manage to make good coating but got small holographic spots)
4. Pure gelatin with mold coating + drying + dipping (2.4% potassium alum, water, 4% and 1% FAC)
5. Pure gelatin with mold coating + dipping right after getting out of mold (2.4% potassium alum, water, 4% and 1% FAC)

Processing methods were:

6. 0.5% and 1.5% H2O2 (developing), water/swelling, then 33-75-91-99 IPA
7. 0.5%, 1% H2O2 (developing), quick water to remove H2O2, 2.4% potassium alum (fixing), water/swelling, then 33-75-91-99 IPA
8. 0.5% H2O2 + 1.2% Potassium alum (developing + fixing in one bath), water/swelling, then IPA bathes

Shooting and processing goes at 28..31C temperature (looks a bit hot but can't really control that, electricity bills would be too big). I've tried to use cold and warm water, even tried to warm or cold developer. Seems water above 40-45C damages emulsion - becomes milky and/or mirror-like reflective color during drying. Cold water or skipping 33/75% IPA as Martin suggested makes a lot of milkyness too somewhy.

So far, my best results were with 4+7 (dipping and processing in H2O2, then fixer) or 4+8 (dipping and processing in H2O2+fixer) with 4% FAC. But i've got these results only for one full batch, failed to repeat that (only small holographic spots with depth in following attempts). Subsequent reprocessing did help to improve quality (looks like after drying with hairdryer it changes some properties).

I've got visible holograms also with 2(both veil and mold coating)+7 also but it did require one-two additional reprocessing to get best quality and it still wasn't really good. Also very big shift to UV usually.
Joe Farina wrote:
Sat Jul 13, 2019 5:49 pm
Personally, I don't like anything involving dipping, during emulsion preparation. It suggests non-uniformity of results. I've had good results incorporating all emulsion components prior to coating.
It could work for me too, but hard to coat pre-hardened emulsion as it is almost gum-like substance. Need something like mayer rod or heating plates i guess. :(
Joe Farina wrote:
Sat Jul 13, 2019 5:49 pm
I can only guess about the necessity of pre-hardening the gelatin (in my case, with MBDCG, this was done with a small amount of chrome alum). I would personally opt to do this in the liquid emulsion (prior to coating). With regular blue exposed DCG, I only had good results when the coated plates (with the ammonium dichromate/gelatin mixture) aged for a certain period of time, to obtain some bias hardness as a whole. I have a feeling that a plain ferric compound/gelatin emulsion would likewise need some bias hardening. I don't know how this material ages (if it dark-reacts at all like DCG). The dark reaction was definitely helpful to me with regular DCG to get some bias hardness. So I would take a closer look at the hardening issue, and if your current hardening agent isn't working (are you sure about the potassium alum?), then I would look for another.
Well, i do have only potassium aluminium sulfate for hardening (well, have can with ammonium dichromate but don't want to open it yet), couldn't find any information on better ones (non-poisonous). It works to some degree, but seems not so good. For example, in my expirements with TEA+dye emulsions - it did more hardening in the end of processing, up to literally strong thin plastic film (although it does peels off glass often). But i don't know how to use this for FAC emulsions, seems TEA isn't compatible with FAC because different chemistry and high pH. Also, i have to process slide one-two times more often to get better results, seems it does better after hot air hardening during drying.

I have an idea to try multi-stage developing to harden it more after developing with dipping into FAC solution, UV-light flooding and into H2O2 again (DCG-processing simulation) but it may damage fringes a lot and very hard to control.
Joe Farina wrote:
Sat Jul 13, 2019 5:49 pm
You've mentioned relative humidity numbers in the 75 to 80% range. These are huge numbers. They may affect the speed of the FAC system (DCG and MBDCG are most sensitive in warm and moist environments). But personally, I wouldn't want to do the processing in such a damp environment, especially if it's fluctuating. In my area, humidity is usually high in the morning, then drops way down in the afternoon. Also, DCG will absorb moisture from the air over 80% and vanish. In the DCG literature, processing in a stable and reasonably low-humidity environment has been recommended. I would think that up to maybe 70% might work (60% and even 50% or lower would likely be better). In my opinion, 75% would be pushing it, and 80% is definitely too high. The stability of the humidity is very important, if you're trying to get consistent results during either exposure or processing. Separating the exposure (high RH) from the processing (low RH) would be fine. But one needs to get a handle on what the RH and temperature are doing first, take the necessary steps, then document them for each exposure and processing session.
Yes, i do shooting in room with 75..95% humidity but do processing (last IPA bathes and drying with hairdryer) at 40..50% humidity. Perhaps i have to shoot at low humidity too, worse sensitivity but less variables at least.
Joe Farina wrote:
Sat Jul 13, 2019 5:49 pm
Yes, it is tedious at first, but if you're serious about getting improvements, then I think it's essential.

It's good your 405nm laser has some coherence. I think some people have had a lot of frustration by finding a 405nm diode that happens to work, frying it by applying too much current, etc., then being unable to find another one which had decent coherence length. If you want to make visible reflection holograms, you could try to make it as broadband as possible, as Martin suggested earlier. I personally don't have much experience with that, but in the wiki section it shows the very broadband Angel hologram made by John Pecora, and he used a plain water soak at the beginning of the process (this is described somewhere in the wiki). So that might be worth looking into. For narrow-band red-shifting, I think the hydrolyzed collagen would be promising, since a fairly long red-shift might be possible with long soak times (a spinner could probably be used to remove the collagen uniformly from the layer).
Yep, got the collagen but failing to get suitable holograms to shift with it now. :(

holomaker
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Re: Ferric ammonium oxalate tests

Post by holomaker » Sun Jul 14, 2019 7:33 am

Not to be a bummer on this thread, but my experience using the 407 nm laser, the dcg holograms are dim looking due to our eyes not being sensitive to this deep blue/purple range. It’s difficult enough to try and get a good DCG hologram w a 530nm or 488 nm laser. You might try and find a more suitable color ......?

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

Re: Ferric ammonium oxalate tests

Post by vasimv » Sun Jul 14, 2019 8:05 am

holomaker wrote:
Sun Jul 14, 2019 7:33 am
Not to be a bummer on this thread, but my experience using the 407 nm laser, the dcg holograms are dim looking due to our eyes not being sensitive to this deep blue/purple range. It’s difficult enough to try and get a good DCG hologram w a 530nm or 488 nm laser. You might try and find a more suitable color ......?
I have 445nm laser which does have at least few millimeters coherence length at 10-20mw and seems suitable for FAC. But FEG's sensitivity is not really good at the wavelength, exposure time is quite big (30 minutes or so for 2% FAC emulsion with 2"x3" slide). :(

Joe Farina
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Re: Ferric ammonium oxalate tests

Post by Joe Farina » Sun Jul 14, 2019 8:42 am

Thanks for the detailed info on your technique. Those temperatures are really high, but maybe you can use that to your advantage, combined with the very high humidity (Wow!) during exposure only. My lab doesn't have air conditioning, and I try not to make holograms in July or August, because everything seems to go haywire due to the elevated temps. If I can't have complete control over both temperature and humidity, I get spooked. Usually, I only expose and process at 18C and 50 to 60% RH for MBDCG. The important thing is control, stability, and monitoring. Ambient temperature and humidity have big effects on DCG.

If you have a special interest in FEG/FAC then by all means continue. Probably many things will be learned that could be applied to traditional DCG, if you choose to go in that direction. But, I have to agree with Dave. 405nm is a difficult wavelength to implement, due to shrinkage issues and the difficulty in red-shifting. But it would be interesting to experiment in this area, if that is your objective. On the other hand, if you want some high-quality holograms in the near future, then I would obtain a proven holographic laser in the green (530-532nm). These are available at decent power levels at reasonably low cost. If you're concerned about dichromate (I don't like the stuff either), then I would take a look at Jeff Blyth's methods for dye-sensitized DCG (I posted a lot of these papers on this forum somewhere, if they're still available). This method requires very little chromate (a very tiny amount). I would guess that you could obtain a suitable dye for green light exposure. The real problem here is obtaining the TMG. On the other hand, there was a fair amount of work done (and formulas published, if I recall correctly) for green-sensitive dye-sensitized DCG without TMG. It might be worthwhile to look at some of these formulas. Some of these appeared to have decent sensitivity, and didn't use the hard-to-find TMG.

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

Re: Ferric ammonium oxalate tests

Post by vasimv » Sun Jul 14, 2019 9:57 am

Joe Farina wrote:
Sun Jul 14, 2019 8:42 am
Thanks for the detailed info on your technique. Those temperatures are really high, but maybe you can use that to your advantage, combined with the very high humidity (Wow!) during exposure only. My lab doesn't have air conditioning, and I try not to make holograms in July or August, because everything seems to go haywire due to the elevated temps. If I can't have complete control over both temperature and humidity, I get spooked. Usually, I only expose and process at 18C and 50 to 60% RH for MBDCG. The important thing is control, stability, and monitoring. Ambient temperature and humidity have big effects on DCG.
Going to try to spend some electricity and freeze room for shooting and processing to 25C or lower. Conditioning temperature to that level will lower humidity a lot too but seems no other options, waiting for winter with its 25..27C temperature wil ltake too much time. :) Unhardened gelatin almost melts at my ambient room temperatures, i guess this ruins resolution a lot - perhaps that is why i'm getting bright colored mirror-like surfaces instead holograms.

Martin
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Re: Ferric ammonium oxalate tests

Post by Martin » Mon Jul 15, 2019 2:00 am

holomaker wrote:
Sun Jul 14, 2019 7:33 am
Not to be a bummer on this thread, but my experience using the 407 nm laser, the dcg holograms are dim looking due to our eyes not being sensitive to this deep blue/purple range. It’s difficult enough to try and get a good DCG hologram w a 530nm or 488 nm laser. You might try and find a more suitable color ......?
Yes absolutely, the violet holograms look pretty dim. That's why I opted for broadband processing. By the way, at 405nm I could easily make broadband DCG - simply developed in tepid water, followed by 94% ethanol. Additional hardening was unnecessary. I believe 405nm hardening is different in nature from say, 532nm. It's probably not just a matter of speed. I don't remember exactly the kind of laser diode I had at my fingertips back then (perhaps a 100mW diode???. it might have run around 50mW). I could easily expose an almost 8x10" area under one minute. That's been the case for ammonium dichromate, potassium dichromate and surprisingly, potassium chromate. FEG, based on FAO was even faster, FAC a bit slower.

I start thinking there's something very special about my standard gelatin. So I'd recommend to look for different kinds/brands of gelatin. Incidentally, some gelatin manufacturers used to hand out free samples. Moreover, chemical integrity of the ferric chemicals is key. Mike Ware's method mentioned earlier, might be definitely worth a try.

As for the point Joe made about RH control during recording, that's undoubtedly of great importance. Just had an idea - not sure if it will work though. You could dry your plates over some saturated salt solution (providing 50-70% RH) in a closed container. When your plate is dry, you'd index match it to a second glass plate by means of white spirit or some other non-hydrophilic, easily removable liquid. That should preserve an RH value within the gelatin layer well below your 75-95% RH environment - at least for a couple of minutes.

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

Re: Ferric ammonium oxalate tests

Post by vasimv » Tue Jul 16, 2019 4:48 pm

Looks like i've ran into combination of three different problems:

1. RainX's leftovers (from mold coating) on emulsion - on last run i've noticed that water comes off plate very quickly on most of area. Washing in IPA does remove that effect, i think it can affect developing/hardening/swelling.
2. Bad drying in new box which i've made for bigger number of plates. Plates didn't dried fully even after 24 hours, they've had even condensate on them.
3. Big shift to UV. Reprocessed some plates and got something visible at least (but still no good holograms, small spots at best). Collagen does cause a lot of milkyness (still practicing with it), citric acid does less red-shift and peels emulsion off even in small concetration but seems less milkyness than with collagen.

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

Re: Ferric ammonium oxalate tests

Post by Joe Farina » Wed Jul 17, 2019 1:16 pm

It's hard to compare my experience to yours, because of your elevated humidity and temps.

So far, I haven't seen milkyness due to collagen. One thing I didn't mention about my milkyness problems involved the alcohol. In some cases, ethyl alcohol produced less milkyness (or what I call "branching" or crystallization) compared to IPA. Sometimes, I've found mixtures of EA/IPA to have better overall performance, compared to either EA or IPA alone.

I've used mold-coating with Rain-x, and in the long run, I settled on Mayer bar coating. With my current gelatin concentration, a #48 bar produces about a 25 micron dry layer. The Mayer bar is used under a homemade laminar flow box. If you don't need to exclude every last speck of dust, it may be possible to just push air through an open box (with some form of filter at the back end of the 4-sided box). I use a window fan mounted on the back of the filter to push air through the filter and rest of the open-end box, where I do the coating with the Mayer bar. If more dust exclusion is needed, some type of "screen" can be added to the air coming off the filter, to make a laminar flow of air. (I use a huge number of drinking straws.) A Mayer bar could probably be made from winding wire (stainless steel) around a rod of some kind, and I've heard that a very large spring can also be used (a large tightly-coiled spring). My Mayer bars were bought from RD Specialties.

Regarding drying after coating (I noted your drying difficulties), I believe it's fairly standard practice to keep the gelatin surface under a gentle air flow (a fan) for a while after coating, overnight is good (around 60% ambient humidity is all I have experience with, though). I use one of my laminar-flow boxes for this purpose also. (I'm not sure if your "drying" problems occurred during molding, or after the cover plate was removed.) For me, Mayer bar coating is faster, and it's easier to make more plates (large plates can also be coated and later cut into smaller ones with a glass-cutter).

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