Rich Rallison

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Rich Rallison

by jsfisher » Sun Apr 29, 2012 8:24 pm

jsfisher wrote:I guess I will have to check my local pharmacy's instant cold packs inventory. (I hope they have not all converted to urea.)
If anyone is interested in getting a small quantity of ammonium nitrate for experimentation, try CVS, if you have them in the area. My local CVS has these in stock: http://www.cvs.com/CVSApp/catalog/shop_ ... dtabdetail . I'm in upstate New York, USA.

(I also found two packages of Curad-brand instant cold packs at a grocery store. One was urea-based, and the other, ammonium nitrate. I had to look inside, though, to find out.)

Rich Rallison

by jsfisher » Fri Apr 27, 2012 9:11 pm

Having read the archive version of the ammonium nitrate discussion, I am a bit confused. It looked like the fact ammonium nitrate was an acid salt and would lower the pH of the gelatin/dichromate solution was being created with the increase in sensitivity. However, a concentrated solution of AN has a pH of about 4.5, so in the amounts being used, I'd think its pH effects would be minor.

On the other hand, the final post in the archived thread mentions the addition of a modest quantity of concentrated ammonia hydroxide to the gelatin/dichromate mixture. Ammonia hydroxide is a moderately strong alkaline, not an acid, so it would seem to contradict the rest of the thread's analysis. (Alas, I do not have access to the referenced journal article.)

Many, many questions come to mind. I guess I will have to check my local pharmacy's instant cold packs inventory. (I hope they have not all converted to urea.)

Rich Rallison

by jsfisher » Fri Apr 27, 2012 6:02 pm

A little search of the archives reveals that ammonium nitrate has come up before. http://holoforum.org/oldforum/viewtopic.php?f=2&t=5288. There are only a handful of posts there, but they are interesting.

Rich Rallison

by dannybee » Thu Apr 26, 2012 9:40 am

jsfisher wrote:Amongst the wisdom of Richard Rallison, I found this:
In Control of DCG and non-sliver holographic materials, SPIE volume 1600, International Symposium on Display Holography, 1991, Rallison wrote:7.6. Sensitizer- We normally use ammonium dichromate crystals or for redder reds Potassium dichromate but the most sensitive of the dichromates (up to three times) is Pyridine dichromate. We don't use it because of its shorter life and difficult preparation. The addition of ammonium nitrate can make the dichromate several times more sensitive, but decreases the useful life and blue shifts the image. Approximate ammonium nitrate concentrations are usually in a ratio of 1 to 5 by weight to ammonium dichromate up to a maximum of 1 to 1 . When the additional substance is washed out of the gelatin a net shrinkage occurs which amounts to a blue shift in reflection holograms and lays down Bragg planes in transmission holograms.
It is the part I marked in bold-italic that interests me. Has anyone here experimented with adding ammonium nitrate to their favorite DCG emulsion formulation? Would potassium nitrate likely be a suitable substitute for ammonium nitrate?
This is very interesting....when I read this it started me to think...the 2 reasons I can see that they use (ammonium) nitrate to make it easy to combine with the (ammonium)dichromate and (nitrate) speed up the aging (hyper-sensitizes) the chrome, we know from others that glycerin can also do this when add to the mix. So I'm wondering if potassium nitrate would work with Potassium dichromate and because it shifts to the red, the replay would be green....it a thought :D

Rich Rallison

by Dinesh » Thu Apr 26, 2012 8:34 am

jsfisher wrote: Has anyone here experimented with adding ammonium nitrate to their favorite DCG emulsion formulation? Would potassium nitrate likely be a suitable substitute for ammonium nitrate?
Not the nitrate, but the fumes from the hydroxide. It's a well known sensitiser, though to give credit where it's due, Dave Trainor from Richmond Holographics put me on to using ammonia as a sensitiser sometime around 82. I don't believe that the potassium salt would work, since the NH3 is the active ingredient. Chemists, correct me if I'm wrong. By the way, it ain't easy exposing your plate to ammonia fumes! The stuff makes the room uninhabitable in seconds. We tried to make some sort of closed chamber whereby we could introduce both the plate and the ammonia in a closed environment, but the ammonia leaked anyway. In the end, the increase in sensitivity wasn't worth the ammonia fumes in your face.

Rich Rallison

by jsfisher » Wed Apr 25, 2012 6:28 pm

Amongst the wisdom of Richard Rallison, I found this:
In Control of DCG and non-sliver holographic materials, SPIE volume 1600, International Symposium on Display Holography, 1991, Rallison wrote:7.6. Sensitizer- We normally use ammonium dichromate crystals or for redder reds Potassium dichromate but the most sensitive of the dichromates (up to three times) is Pyridine dichromate. We don't use it because of its shorter life and difficult preparation. The addition of ammonium nitrate can make the dichromate several times more sensitive, but decreases the useful life and blue shifts the image. Approximate ammonium nitrate concentrations are usually in a ratio of 1 to 5 by weight to ammonium dichromate up to a maximum of 1 to 1 . When the additional substance is washed out of the gelatin a net shrinkage occurs which amounts to a blue shift in reflection holograms and lays down Bragg planes in transmission holograms.
It is the part I marked in bold-italic that interests me. Has anyone here experimented with adding ammonium nitrate to their favorite DCG emulsion formulation? Would potassium nitrate likely be a suitable substitute for ammonium nitrate?

Rich Rallison

by a_k » Sat Feb 11, 2012 2:03 pm

Thanks for telling, Joe. I've contacted Wasatch Photonics, they seem to have had a cooperation with R. Rallison. Maybe they have some contact information.

Rich Rallison

by Joe Farina » Sat Feb 11, 2012 12:22 pm

I don't know if Ralcon still exists. Before Rich Rallison passed away, I think the township shut his business down due to zoning violations.

Rich Rallison

by a_k » Sat Feb 11, 2012 11:22 am

Does anybody know how to contact the people at Rallisons lab - Ralcon? The email addresses on the archived website don't seem to work. My mails keep bouncing back to me.

Rich Rallison

by Joe Farina » Thu Feb 02, 2012 9:56 am

That's a great idea, Ahmet, good luck.

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