Ferric ammonium oxalate tests

[Martin]

Congratulations! That looks very promising. The white color of the dry layer seems to indicate some layer damage. Maybe the water was simply too warm?

I'd skip the potassium aluminium sulfate step.

Without fixer a lot of emulsion gets washed off in water. And wasn't able to get something near that without warm water.

So your water temperature seems to be too high. With my standard FEG gelatin I usually can't go higher than 30C.
Note also that when you insert your plate into the water right after the H2O2 step the gelatin becomes very vulnerable to damage.
To prevent that you might use COLD water (<20C) to remove the H2O2. Only then you'd use a water (swelling) bath at 25-30C. But that temperature depends on your type of gelatin of course. For broadband reconstruction to have to go right to the threshold temperature (the temperature the gelatin can take without damage). You then could directly apply 100% alcohol for dehydration. I didn't notice much of a difference between ethanol and isopropyl alcohol. So I stayed with the much cheaper ethanol.

Failed to get anything useful with my 405nm at bigger depth, must be really bad laser - only few millimeters deep and nothing visible after.

I'm familiar with that problem. I never had a 405nm laser with more than 2mm coherence length. I keep looking for a 405nm laser with reasonable coherence length and a reasonable price (the Ondax lasers seem a bit over the top in that regard).

A bit confused. Couldn't get a reflective hologram but did copy a transmission one with 405nm laser (the master was made with red laser on litiholo film, i just placed the film on FAC emulsion plate under beam to get direct transmission copy).

I also use a transmission grating on top of my recording materials. Usually this comes on top of a coin also. So I can record a reflection and transmission hologram at the same time.

Perhaps i did something wrong as i see only small part of it at weird replay angle (with any laser) but did work still, it has original's depth and reflections from sides when i look from different angles. Not sure why i keep failing with reflective holograms, may be it is layer's thickness or my processing method.

Yes, layer thickness difference may be an issue (e.g. too much FAC or a not entirely dry layer before recording).

[vasimv]

So your water temperature seems to be too high. With my standard FEG gelatin I usually can't go higher than 30C.
Note also that when you insert your plate into the water right after the H2O2 step the gelatin becomes very vulnerable to damage.
To prevent that you might use COLD water (<20C) to remove the H2O2. Only then you'd use a water (swelling) bath at 25-30C.

Will try cold water, thank you. Temperature is about 30C here usually and possible because this i get gelatin layer damaged almost always, especially as i don't dry plates too long time usually to save time.

Btw, i've noticed a lot of small air bubbles sitting on top of layer during 99% IPA bath on very milky areas. Can be these are product of high H2O2 concetration as described in one of papers?

[Martin]

Btw, i've noticed a lot of small air bubbles sitting on top of layer during 99% IPA bath on very milky areas. Can be these are product of high H2O2 concetration as described in one of papers?

I guess you those air bubbles are concentrated on the softest spots (where H2O2/free radical attack or insufficient drying were most pronounced).

[vasimv]

With cold water it is getting weird, gelatin stays even on underexposed areas and no diffraction patterns although i get coins reflections as always. No holograms, even transmission copy did fail.

Also tried speedball diazo emulsion (PVA + diazo sensitizer + something else), it is quite sensitive to 405nm laser (above FAC). But the emulsion itself blocks much of light and obviously isn't possible to get a reflection hologram and transmission ones won't be good. I was able to get small area with diffraction pattern from transmission hologram copy but it was too weak and i couldn't reproduce the effect. Will try the sensitizer with pure PVA later.

[Martin]

With cold water it is getting weird, gelatin stays even on underexposed areas and no diffraction patterns although i get coins reflections as always. No holograms, even transmission copy did fail.

Too bad. It looks like one of the main difficulties with FEG stems from the unreliability of the commercially available chemicals. FAC (= ferric ammonium citrate or ammonium ferric citrate) e.g. is available in various qualities with different iron concentrations. On Mike Ware's homepage (www.mikeware.co.uk/mikeware/main.html) there is a recent paper called "Simple Cyanotype" (www.mikeware.co.uk/downloads/SimpleCyan.pdf). 'Simple Cyanotype' "avoids commercial ferric ammonium citrate altogther but effectively makes it in situ, easily and cheaply, from widely-available pure chemicals." It requires ferric nitrate, citric acid and ammonia. That's a very interesting approach. I plan to give it a try shortly.

Also tried speedball diazo emulsion (PVA + diazo sensitizer + something else), it is quite sensitive to 405nm laser (above FAC). But the emulsion itself blocks much of light and obviously isn't possible to get a reflection hologram and transmission ones won't be good. I was able to get small area with diffraction pattern from transmission hologram copy but it was too weak and i couldn't reproduce the effect. Will try the sensitizer with pure PVA later.

Sounds very promising! Did you notice a color change from the laser exposure?

[vasimv]

I've got an idea why it is so hard with FEG. Not that i really understand what is going on but as i know dichromates do harden the gelatin. FAC/FAO don't harden it so much (or at all), so we get very soft layer of emulsion which is very hard to process to get something useful. I'll try to make emulsions with small amount of potassium alum, may be this will help. Perhaps formaline would be better option as alum will react with some of FAC for sure but don't have found it nearby.

Too bad. It looks like one of the main difficulties with FEG stems from the unreliability of the commercially available chemicals. FAC (= ferric ammonium citrate or ammonium ferric citrate) e.g. is available in various qualities with different iron concentrations.

May be because it gets exposed to light during transportation and storage? I guess, if they keep those salts in white plastic cans - under some violet/blue light it'll degrade a lot.

Sounds very promising! Did you notice a color change from the laser exposure?

Well, so far i got just PVA-free spots where shadows were (from objects lying on top of glass). I've got some unwashed PVA in those areas, it got color changed from gree to blue a bit. Btw, it was a bit surprise as i've thought the PVA will get washed off on exposed areas.

[Martin]

I've got an idea why it is so hard with FEG. Not that i really understand what is going on but as i know dichromates do harden the gelatin. FAC/FAO don't harden it so much (or at all), so we get very soft layer of emulsion which is very hard to process to get something useful.

Yes, you're probably right. One key difference between the two, DCG and FEG (particularly based on FAC) is that ferric agents represent a far lower health risk than dichromates. Hence, FAC is much easier to purchase than dichromate - particularly here in Europe.

Too bad. It looks like one of the main difficulties with FEG stems from the unreliability of the commercially available chemicals. FAC (= ferric ammonium citrate or ammonium ferric citrate) e.g. is available in various qualities with different iron concentrations.

May be because it gets exposed to light during transportation and storage?

I think it's mainly a matter of chemical purity.

Btw, it was a bit surprise as i've thought the PVA will get washed off on exposed areas.

Are you sure it's PVA (PVOH) and not PVAC (polyvinyl acetate)?

[vasimv]

Are you sure it's PVA (PVOH) and not PVAC (polyvinyl acetate)?

Oops, you're right. I was sure about PVA but checked MSDS for the emulsion, it says "vinyl acetate" ( https://www.speedballart.com/wp-content ... ulsion.pdf ). Damn, the sensitizer may not work with PVA.

[Martin]

I was sure about PVA but checked MSDS for the emulsion, it says "vinyl acetate" ( https://www.speedballart.com/wp-content ... ulsion.pdf ). Damn, the sensitizer may not work with PVA.

Probably not (and gelatin neither). But maybe your Speedball thing could be used anyway. The MSDS suggests the vinyl acetate gets polymerized into polyvinyl acetate. I recall there are plenty of diazos generating free radicals.

By the way, the stuff here, "Diazo Sensitizer" (https://www.speedballart.com/wp-content ... 11/398.pdf) might be better adapted for gelatin or PVA. It's said to be water soluble.

[vasimv]

By the way, the stuff here, "Diazo Sensitizer" (https://www.speedballart.com/wp-content ... 11/398.pdf) might be better adapted for gelatin or PVA. It's said to be water soluble.

Yes, it is water solluble for sure, you have to add some water to the sensitizer bottle before use. I've read some controversy report about the speedball sensitizer with gelatin on a forum. It looks like the sensitizer does damage the gelatin in some way. Well, i have feeling that PVA will be much easier than gelatin anyway.

Yesterday did test with FAC (2g per 100ml of emulsion) + potassium aluminium sulfate (0.5g), cold (about 10C temperature) 0.5% H2O2 developer (to prevent gelatin dissolve by water in the developer before it gets polymerized) and 40..45C water bath after. Results are quite strange, i see bright colors are all over emulsion during 91% IPA bath (green and red mostly) and 99% IPA (shifting to blue) but after i try to dry slides with hair dryer - it turns to white mostly. I can repeat the process by dipping it into water and going through IPA baths again (31+75+91+99 at 29..30C) but after drying it gets just milky again. Annoying. Possible because i didn't dried emulsion before exposure good (just few minutes with hair dryer), will try with good dried emulsion today and test with normal temperature H2O2.