Martin tests 2

Dichromated Gelatin.
Dinesh

Martin tests 2

Post by Dinesh » Fri Mar 16, 2012 11:41 am

Martin
I just coated plates with your gelatin and FAO in the same proportions:
30 gms gelatin
6 gms FAO
300 mls water
3 drops of Kodak Photoflo

Will shoot same as before and see if the gelatin makes any difference. As always, I'll post results here.

Martin

Martin tests 2

Post by Martin » Sat Mar 17, 2012 4:43 am

Dinesh wrote:Martin
I just coated plates with your gelatin and FAO in the same proportions:
30 gms gelatin
6 gms FAO
300 mls water
3 drops of Kodak Photoflo

Will shoot same as before and see if the gelatin makes any difference. As always, I'll post results here.
OK, thanks a lot.
If you illuminate the FAO/gelatin layer with your 457nm laser, do you notice any significant light absorption?

Dinesh

Martin tests 2

Post by Dinesh » Sat Mar 17, 2012 9:11 am

Martin wrote:If you illuminate the FAO/gelatin layer with your 457nm laser, do you notice any significant light absorption?
I'll check for this.

Dinesh

Martin tests 2

Post by Dinesh » Fri Mar 23, 2012 10:36 am

So, 10 plates exposed at 2.2mW. Develop:
10 secs in 1% hydrogen peroxide
5 min in running water
dry in IPA as per standard dcg

Absorption:
Reading before plate (ie the ref) = 1.86
Reading after plate = 1.80
Hence absorption = (1.86 - 1.80)/1.86 ~ 3.2%

No change in sensitivity due to softer gelatin. However, the plates had a white haze, presumably due to the softer gelatin (I did not fix, since I was trying to reproduce the original procedure). Good exposures were attained at roughly 300 mJ. However, I increased the percentage of peroxide to 2% and got significantly better results. The 300mJ exposure was noticeably brighter after processing in the increased peroxide concentration.

Martin

Martin tests 2

Post by Martin » Sat Mar 24, 2012 3:36 am

Dinesh wrote:Absorption:
Reading before plate (ie the ref) = 1.86
Reading after plate = 1.80
Hence absorption = (1.86 - 1.80)/1.86 ~ 3.2%
That doesn't look like huge absorption. I guess at 405nm I may have had 20% or so.
How much light do your standard DCG plates absorb at 457nm?

Assuming you cannot increase FAO concentration much further, switching to another ferric salt might become a serious option. My blue LUMILED - still waiting for a nice blue laser...- indicates far better absorption for FAC (ferric ammonium citrate) than FAO.
No change in sensitivity due to softer gelatin. However, the plates had a white haze, presumably due to the softer gelatin (I did not fix, since I was trying to reproduce the original procedure). Good exposures were attained at roughly 300 mJ. However, I increased the percentage of peroxide to 2% and got significantly better results. The 300mJ exposure was noticeably brighter after processing in the increased peroxide concentration.
So far the good news. I'm not particularly impressed with the 300mJ though (at 405nm I might have exposed the plates at 1 - 5mJ - occasionally 0.5mJ only).

Dinesh

Martin tests 2

Post by Dinesh » Mon Mar 26, 2012 10:48 am

Martin wrote:Assuming you cannot increase FAO concentration much further
Well, I put in 6gms of FAO in 300 mls water, as per the original instructions. I can presumably load more FAO into it. In fact, I was going to try doubling the FAO concentration next. I assume that there will be a point when the FAO will saturate, but 6 gms dissolved very quickly. Also, I forgot to mention that I put in 3 drops of Kodak Photoflo; you mentioned that this was an essential part of the formulation. Yes, 300 mJ is not very good, but it may get better with increased FAO. By the way, what if I mix the FAO with FAC?
Martin wrote:How much light do your standard DCG plates absorb at 457nm?
You know, I never measured this! Anyway, here's an illustration from "Topics in Applied Physics", vol 20 "Holographic Recording Materials" ed H. M. Smith. The illustration itself is taken from papers by Shankoff* and B. O'Brian**
DCGabsorb005.jpg
DCGabsorb005.jpg (14.66 KiB) Viewed 3022 times

*T. A. Shankoff: "Applied Optics" 7, pp 2101 (1968)
**B. O"brian: "J. Opt. Soc. Am. 42, p. 101 (1952)

Martin

Martin tests 2

Post by Martin » Tue Mar 27, 2012 6:21 am

Dinesh wrote:
Martin wrote:Assuming you cannot increase FAO concentration much further
Well, I put in 6gms of FAO in 300 mls water, as per the original instructions. I can presumably load more FAO into it.
Good. Let's see if you'll get some significant absorption from your blue laser. You might simply verify that with a FAO solution without adding any gelatin...
In fact, I was going to try doubling the FAO concentration next. I assume that there will be a point when the FAO will saturate, but 6 gms dissolved very quickly.
Yes, I remember having heard photo people say, gelatin could take much more FAO than dichromate - maybe up to 3x the quantity of dichromates.
Also, I forgot to mention that I put in 3 drops of Kodak Photoflo;
Right - actually my surfactant was Triton-100.
Yes, 300 mJ is not very good, but it may get better with increased FAO. By the way, what if I mix the FAO with FAC?
Yes, that might be worth a try.
On the other hand, I now really wonder if FAC wouldn't be more appropriate to blue recordings. Photographic wisdom used to claim far better speed for FAO than FAC. But then, wasn't that essentially based on broadband UV exposures?
FAC has some benefits: it's much less toxic. Hence it's easier to purchase than FAO (by the way, you'd have to look for the green stuff, not the brown one).


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[quote="Martin"]How much light do your standard DCG plates absorb at 457nm?[/quote]
You know, I never measured this!


I see - thanks for reminding me of Shankoff. So how does your ammonium dichromate solution look like under your blue laser (and how does it compare with FAO or FAC solutions)?

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