FEG (ferric gelatin) holograms

[a_k]

Very impressing result, Martin, congratulations. This alternative to the hard to get Chromates/Dichromates is very welcome.

I was fearing that the sensibility of FEG would be low but apparently this is not the case.

The FEG hologram on your picture looks very clear and has a nice colour. Did it take any special treatment to get this replay color? I remember how my 405nm DCGs were too blue and had a tendency to disappear in the UV.

Just finished coating my first FEG plates with FAC, i'm very curious about the outcome.

There is a simple way of electrolytically synthesizing Ammoniumferriccitrate, i'll put a recipe in a separate thread.

[Sergio]

This is superb, completely amazing..

This is a metal ion crosslinking reaction so it can be sensitized by methylene blue and TMG as electron donor if the mechanism is reduction of ferric, to ferrous ion (it decrosslink the gelatin?).

I found a note by G.OSTER that the analogue mercuric chloride (TOXIC) works nice with a photoreducible dye, at high pH, using eosine proflavine and methylene blue, also a variety of metal ions can be reduced, Fe2+ ,Ti4+, Cu2+ ,Ag+ and MoO4 2-.

[Martin]

Very impressing result, Martin, congratulations. This alternative to the hard to get Chromates/Dichromates is very welcome.

I was fearing that the sensibility of FEG would be low but apparently this is not the case.

The FEG hologram on your picture looks very clear and has a nice colour. Did it take any special treatment to get this replay color? I remember how my 405nm DCGs were too blue and had a tendency to disappear in the UV.

Just finished coating my first FEG plates with FAC, i'm very curious about the outcome.

There is a simple way of electrolytically synthesizing Ammoniumferriccitrate, i'll put a recipe in a separate thread.

Thank you Ahmet.
I also noticed extremely low noise violet reconstructions – unfortunately they are visible with the Bluray diode only. I of course tried a couple of post-processing methods but none proofed to work reliably – as of yet.
To make a broadband reconstruction like the one shown in the picture, I was forced to push the gelatin layer to its limit. The temperature of the swelling bath was close to the maximum the gelatin could take – ~28°C with that kind of gelatin and particular layer thickness.
I then directly applied the “Brennprit” (94% ethanol + 2% MEK) with a small hand pump spray (like this one http://cgi.ebay.co.uk/Water-Spray-Bottl ... otohosting).
The last step consisted in spraying a 50%/50% mixture of the above mentioned “Brennsprit” with acetone before the hot air drying. So no IPA was used in that case.

In connection with SHSG and DCG I've been using these pump sprays with alcohols for quite some time.
One advantage of this method is you won't have to bother about monitoring the concentration of your alcohol baths. Moreover, quite fast processing can be done: for the FEG holograms, it took probably less than two minutes from the swelling bath to the final hologram.
Most likely though, this method will have its limits when it comes to processing larger formats and thicker gelatin layers.

As for your electrolytic synthesis of FAC, it's simply amazing!

[Martin]

This is superb, completely amazing..

This is a metal ion crosslinking reaction so it can be sensitized by methylene blue and TMG as electron donor if the mechanism is reduction of ferric, to ferrous ion (it decrosslink the gelatin?).

I found a note by G.OSTER that the analogue mercuric chloride (TOXIC) works nice with a photoreducible dye, at high pH, using eosine proflavine and methylene blue, also a variety of metal ions can be reduced, Fe2+ ,Ti4+, Cu2+ ,Ag+ and MoO4 2-.

I am not sure the methods used for spectrally sensitized DCG could be applied to FEG. I've to reread Oster. Most (all?) these methods considerably raise the pH value – most notably TMG. It looks though FEG loves low pH ranges.
Having said that, I all the same highly appreciate any attempt to take a look backwards into “classic litterature”. Let's not forget the “new” FEG thing actually goes back almost 200 years! By the way, some time ago there used to be that interesting paper by Eder (The chemical effect of the spectrum) available online. It's not longer there. Luckily, it can be brought back again through the way-back-machine: http://web.archive.org/web/200307142208 ... s/eder.pdf

[salvee]

This is an exciting development in the field of holographic recording materials. From my point of view, the most exciting thing about FEG is that it is the reverse of DCG. DCG has to start off with relatively soft gel, which is hardened by optical radiation to record fringes. The dark reaction also hardens the gel- hence the short shelf life of DCG emulsions.
FEG, on the other hand, starts with hard gel; optical radiation breaks the gel bonds, softening the gel.
One question that springs to mind is- does FEG suffer from a dark reaction too- i.e. over time does the Ferric compound break down gel bonds, softening the gel to a point where it becomes useless? If so, how long does it take in normal storage conditions?
If the dark reaction is much slower than for DCG, it would be possible to store the FEG plates for a long time- maybe long enough to make it viable to produce the plates commercially.

[a_k]

Salvee, i would think FEG does the same as DCG, the regions that receive light get crosslinked (hardened).

Only the mechanism is different. In DCG it is Cr3+ that does the crosslinking, in FEG it is neither Fe3+ nor Fe2+ but the radicals which result from the rection of Fe2+ with the developer substance in the illuminated regions.

According to the Chiba paper there is no dark reaction with FEG, because gelatine does not reduce Fe3+.

Concerning shelf life, i have no idea.