Ferric ammonium oxalate tests

Dichromated Gelatin.
vasimv
Posts: 58
Joined: Tue Apr 23, 2019 2:16 am

Re: Ferric ammonium oxalate tests

Post by vasimv » Tue Jun 25, 2019 9:28 am

A little success again, with mold gelatin coating + dipping method. The method was a bit complicated and gave not really good results (emulsion's surface got damaged from condenstate after fridge and stains from pre-hardening/sensitizing) but uniform thickness did help and i've managed to get holograms on all plates, although most of them got faded out and/or shifted into UV overnight. Got one stabilized after multiple reprocessing and baking for 2 hours at 85C, but it lost contrast and went a bit milky. I guess, i'll need more thick emulsion. Interesting, they all were very deep red in 99% IPA bath but went green/blue after drying.
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Coating was done with 3 layers of scotch #500 tape and 12% gelatin, i think it is something like 110 microns wet thickness total. Then i've dried for 6 hours and dipped for 1 minutes into 2.4% potassium alum solution, then 30 seconds in water and 1 minute in 4% FAC solution, then dried again for 8 hours at 50..60% humidity. I've included one more bath in potassium alum after developing (as i wasn't able to re-process first hologram in the batch again without damaging it), but not sure if that was really neccessary.
For hardening gelatin, my preferred method is using chrome alum. I don't know if this is compatible with your ferric system, though. For example, one of my batches was mixed as follows: 0.5ml of a 5% chrome alum solution added to 47ml (room temperature) water, then 6 grams gelatin mixed into this and allowed to soak a while, then temperature raised to 44C.
Well, i don't want to mess with chromium stuff and potassium alum does quite good, so i'll try to decrease its concetration in emulsion just. Anyway, i've found that i can mix both H2O2 developer and potassium alum solution (and both chemicals keeps their properties in the mix - i've got hologram fully developed in that), so the emulsion gets hardened right during developing, much like dichromated gelatin does during exposure. Perhaps i won't need pre-hardening even.

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

Re: Ferric ammonium oxalate tests

Post by Joe Farina » Tue Jun 25, 2019 11:37 am

Nice result. After suggesting chrome alum, I realized that the reason you're using the ferric system is probably because you want to stay away from chromium compounds :)

Regarding blue-shifting (shrinkage) of DCG during and after processing, I've had these issues also (possibly due to the TMG content of my MBDCG). One thing I've found to be important is the rapidity of drying after leaving the last alcohol bath. It must be as fast as possible, every second counts.

vasimv
Posts: 58
Joined: Tue Apr 23, 2019 2:16 am

Re: Ferric ammonium oxalate tests

Post by vasimv » Tue Jun 25, 2019 6:13 pm

Joe Farina wrote:
Tue Jun 25, 2019 11:37 am
One thing I've found to be important is the rapidity of drying after leaving the last alcohol bath. It must be as fast as possible, every second counts.
Thanks, did reprocess one of those with full heat blast from hair dryer in one second after last IPA. Seems less shift to blue (or more to red actually, as it was shoot with 405nm): https://www.youtube.com/watch?v=IbGwfn3rOQ4

Grayham
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Joined: Wed Feb 11, 2015 12:56 pm
Location: Hampshire, UK

Re: Ferric ammonium oxalate tests

Post by Grayham » Wed Jun 26, 2019 7:24 am

That is a good result. Your method is starting to look really promising.

Martin
Posts: 92
Joined: Sat Apr 04, 2015 2:36 am

Re: Ferric ammonium oxalate tests

Post by Martin » Wed Jun 26, 2019 9:09 am

Quite impressive progress!

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

Re: Ferric ammonium oxalate tests

Post by Joe Farina » Wed Jun 26, 2019 9:57 am

Wow, that's an amazing ferrogram! Congratulations Vasimv and Martin. If you recorded at 405 it looks like you're getting over 100nm red-shift and a nice green narrowband hologram.

If you dry this hologram by heating in an oven, I think there is little doubt there will be a big blue shift. The heat will cause the matrix of planes to gradually get more and more compact, and the layer will shrink. This also happens during the initial drying (after the last alcohol) but during oven drying the shrinkage rate seems much slower. A hair dryer after the last alcohol bath appears to work for you, but I think a heat gun will be better. For the final drying (instead of using an oven) I would suggest looking into a food dehydrator. This dries material very effectively with forced air, and can apply the minimum amount of heat (the amount of heat is adjustable). I use one like this: https://www.walmart.com/ip/Excalibur-5- ... gKe7fD_BwE

vasimv
Posts: 58
Joined: Tue Apr 23, 2019 2:16 am

Re: Ferric ammonium oxalate tests

Post by vasimv » Wed Jun 26, 2019 10:22 am

Thank you, guys, couldn't do without your help and advices. I hope to get better ones soon (just did mold coating with a bit thicker emulsion and managed to get very clear and smooth surface, so it shouldn't be so misty and foggy).

But one thing bothers me really. I'm getting this hologram replay at very strange replay angle (very different from recording, literally at opposite of that), with some geometric distortions (as you may see, shadows are going in opposite directions, like when hologram was recording, background looks a bit far from coins than it is in reality). If i do replay at same angle - the image doesn't seem to have distortions but color is violet/near UV (same as laser's color) and barely visible. Looks like i didn't get red-shift actually, but kind of strange replay effect. When i did reflection holograms with litiholo films - i didn't observe such effect, they were visible only under same angle.
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Update: Failed test with mold coating and 4 layers of scotch tape (140..160 microns wet emulsion, about 45..60 microns dry thickness), just nice colored coins reflections, more red and a lot milkyness at low exposures and green with some milkyness at higher. Got few very small holographic spots where depth is visible and nothing else. Emulsion wasn't pre-hardened (standard mix with 12g gelatin + 2g FAC for 100ml emulsion), developed in mix of 0.5% H2O2 and 2.4% Potassium aluminium sulfate for 2 minutes (to be sure, did one slide in separate H2O2 and hardener solutions - same). Reprocessing with more water bathes didn't help in any way. Some small bubbles visible on whole emulsion layer (problem with developer getting inside or gases coming out during development, i guess). Will do next test with same emulsion and 2 or 3 layers of tape, then switch to pre-hardened again.

Martin
Posts: 92
Joined: Sat Apr 04, 2015 2:36 am

Re: Ferric ammonium oxalate tests

Post by Martin » Thu Jun 27, 2019 3:10 am

vasimv wrote:
Wed Jun 26, 2019 10:22 am


But one thing bothers me really. I'm getting this hologram replay at very strange replay angle (very different from recording, literally at opposite of that), with some geometric distortions (as you may see, shadows are going in opposite directions, like when hologram was recording, background looks a bit far from coins than it is in reality). If i do replay at same angle - the image doesn't seem to have distortions but color is violet/near UV (same as laser's color) and barely visible. Looks like i didn't get red-shift actually, but kind of strange replay effect. When i did reflection holograms with litiholo films - i didn't observe such effect, they were visible only under same angle.

Sounds like some harmonics effect, maybe through over-modulation. I've had that too.

Referring to your barely visible violet image, did you ever try to reconstruct it with your 405nm laser at approx. the recording angle? I remember having seen extremely high quality (and close to 100% DE probably) low noise images at 405nm.

vasimv
Posts: 58
Joined: Tue Apr 23, 2019 2:16 am

Re: Ferric ammonium oxalate tests

Post by vasimv » Thu Jun 27, 2019 10:00 pm

Martin wrote:
Thu Jun 27, 2019 3:10 am
Referring to your barely visible violet image, did you ever try to reconstruct it with your 405nm laser at approx. the recording angle? I remember having seen extremely high quality (and close to 100% DE probably) low noise images at 405nm.
One of two remained slides doesn't replay with UV laser at all (but does with UV-A flashlight), second does. I can't tell if it is really better or worse than green image from opposite angle, very hard to compare. Contrast looks same or may be slightly better in UV.

Update: They actually replay from backside too, with quite small loss of quality and some geometric distortion. I've made video to show it (it is same from previous video, just got few test reprocessings): https://www.youtube.com/watch?v=3HrxZoA7neg

vasimv
Posts: 58
Joined: Tue Apr 23, 2019 2:16 am

Re: Ferric ammonium oxalate tests

Post by vasimv » 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.
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So, it is one of possibilities:

1. Something changed in the environment (temperature, humidity, quality of tap water i've used for bath) - not really possible as we have quite same conditions here whole year.
2. 2% FAC emulsion has very different properties than sensitized by dipping in 4% FAC solution (sensitivity, possible crystallization or different distribution through layer) - possible, but i doubt that. The sensitivity did look quite same, btw.
3. Emulsion gets damaged by cold in fridge (sure above 3C) - very low chances i think.
4. Too thin still (with 4 layers and same emulsion/processing i've got very small spots with hologram but nothing at all with 2 or 3 layers). Although with pre-hardened emulsion it was done with 3 layers just, so low chances too.
5. Without pre-hardening - the emulsion does record some diffraction patterns but recording a reflective hologram is nearly impossible.

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