Ammonium Dichromate in the UK

dcgman · Post by **dcgman** » Mon Dec 05, 2011 2:38 pm

Does anyone in this forum know where I can buy Ammonium Dichromate in the UK. 'Silverprint' used to sell it, but it's no longer in their catalogue. Has it been banned from general sale? if so, it's yet another nail in the coffin for amateur holographers!

Jem · Post by **Jem** » Mon Dec 05, 2011 11:29 pm

Hi

Have you tried Camlab?

http://www.camlab.co.uk/ammonium-dichro ... 14915.aspx

Or here

http://www.timstar.co.uk/Item/Chemicals ... 1246/.html

Not sure how you'll get on as a private individual though as a lot of these companies will now only sell to other companies or educational establishments where a full audit trial can be implemented.

Failing that, there's some for sale in the USA Ebay site: http://www.ebay.co.uk/itm/Vintage-Malli ... 4ab16eb959

Cheers

Jem

Martin · Post by **Martin** » Tue Dec 06, 2011 4:11 am

dcgman wrote:Does anyone in this forum know where I can buy Ammonium Dichromate in the UK. 'Silverprint' used to sell it, but it's no longer in their catalogue. Has it been banned from general sale? if so, it's yet another nail in the coffin for amateur holographers!

What's the wavelength you're shooting at? I ask because in case exposures were done below 480nm, maybe 470nm, you might consider ferric sensitized gelatin (FEG). Having had no access to a blue laser as of yet, I've been unable to verify myself if FEG could be successfully used at other wavelengths than 405nm.

As an aside, I keep looking into alternatives for DCG. Currently, I got a dichromate-free thing working nicely for red exposures. Speed is pretty good, not that far from AgX. It could be easily turned into an RGB sensitized recording material. I actually call this system "MSG" (= monomer sensitized gelatin). Unlike most of nowadays holographic photopolymers, this one does require wet processing à la DCG. But then, it allows to achieve results very similar to DCG. Currently, I'm searching for monomer mixtures that are less toxic since I figure it wouldn't make much sense replacing the dichromate with some other "nasty" ingredient...

dannybee · Post by **dannybee** » Tue Dec 06, 2011 10:56 am

Martin wrote:As an aside, I keep looking into alternatives for DCG. Currently, I got a dichromate-free thing working nicely for red exposures. Speed is pretty good, not that far from AgX. It could be easily turned into an RGB sensitized recording material. I actually call this system "MSG" (= monomer sensitized gelatin). Unlike most of nowadays holographic photopolymers, this one does require wet processing à la DCG. But then, it allows to achieve results very similar to DCG. Currently, I'm searching for monomer mixtures that are less toxic since I figure it wouldn't make much sense replacing the dichromate with some other "nasty" ingredient...

what monomer are you using?

Dinesh · Post by **Dinesh** » Tue Dec 06, 2011 3:28 pm

Martin wrote: I ask because in case exposures were done below 480nm, maybe 470nm, you might consider ferric sensitized gelatin (FEG). Having had no access to a blue laser as of yet, I've been unable to verify myself if FEG could be successfully used at other wavelengths than 405nm.

If you give me the formula for FEG, I can try it at blue wavelengths. I have a laser at 457.

Martin · Post by **Martin** » Wed Dec 07, 2011 3:11 am

dannybee wrote:what monomer are you using?

Acrylamide and various other monomers.

Martin · Post by **Martin** » Wed Dec 07, 2011 3:12 am

Dinesh wrote:If you give me the formula for FEG, I can try it at blue wavelengths. I have a laser at 457.

That sounds exciting, thanks for trying, Dinesh!

Due to better keeping properties/photo speed I'd opt for ferric ammonium oxalate (FAO) rather than ferric ammonium citrate (FAC). I suspect FAC may show higher light absorption around 458nm though.
A safe start for a 458nm recording would probably involve some 0.2g FAO per gram gelatin (culinary pig gelatin). I used to handle 10% ferric stock solutions.
For coating I did apply 5 - 10% gelatin (+FAO) solutions. Layer thickness may be something to experiment with, since it does require some fine tuning to get optimum results (in that respect FEG is definitely not as "tolerant" as DCG). One key thing I came to realize much later was the importance of adding a surfactant. This seems to be directly linked to photo speed. Both Triton-100 and Tween 20 worked nicely. 1-2 drops from a 1% stock solution were added to 10ml coating solution.

After exposure, the layers have to be "developed" in a 1% hydrogen peroxide solution for up to 10s. They're then washed in cold water and put into a water swelling bath at 20-30°C (with this particular kind of gelatin) before they're deyhdrated in alcohol à la DCG.

Dinesh · Post by **Dinesh** » Wed Dec 07, 2011 6:46 pm

So, let me get this right:
5 - 10 gms of gelatin per 100 mls of water and 0.2 gms FAO/gram gelatin. If I use 300 mls of water, I add 30 gms gelatin and 6 gms FAO?

Martin · Post by **Martin** » Wed Dec 07, 2011 11:39 pm

Dinesh wrote:So, let me get this right:
5 - 10 gms of gelatin per 100 mls of water and 0.2 gms FAO/gram gelatin. If I use 300 mls of water, I add 30 gms gelatin and 6 gms FAO?

Correct.