Milkyness in dcg

Dichromated Gelatin.
Joe Farina
Posts: 724
Joined: Wed Jan 07, 2015 2:10 pm

Milkyness in dcg

Post by Joe Farina » Sat Feb 23, 2013 10:06 am

I'm using a post-exposure bath which works well, as follows:

Part 1: Sodium Metabisulfite (1% solution in water)
Part 2: Aluminum Sulfate (0.2% solution in water)

Before use, I mix equal volumes of 1 and 2, and soak the exposed plate for about 2 minutes.

This system has a number of advantages. First, these chemicals are cheap and comparatively pleasant to use. Second, the concentrations can easily be changed to suit your needs. The sulfite appears to promote reduction, and the alum provides some bias hardening. The time in the bath can be changed also, of course.

Thanks to John Pecora and Jeff Blyth for your research.

Note: As I recall, Jeff had mentioned to me that potassium metabisulfite should probably work in a similar way compared to the sodium. There are many types of "alum" but I would suggest trying the Aluminum Sulfate first.

MilanKarakas

Milkyness in dcg

Post by MilanKarakas » Sun Feb 24, 2013 9:10 am

Joe Farina wrote:I'm using a post-exposure bath which works well, as follows:

Part 1: Sodium Metabisulfite (1% solution in water)
Part 2: Aluminum Sulfate (0.2% solution in water)
Thank you Joe for the recipe. I think this will help on my future work.
Joe Farina wrote:Before use, I mix equal volumes of 1 and 2, and soak the exposed plate for about 2 minutes.
I suppose after use, it should be disposed? It can't be stored for late use?
Joe Farina wrote:This system has a number of advantages. First, these chemicals are cheap and comparatively pleasant to use. Second, the concentrations can easily be changed to suit your needs. The sulfite appears to promote reduction, and the alum provides some bias hardening. The time in the bath can be changed also, of course.
That sounds good.
Joe Farina wrote:Thanks to John Pecora and Jeff Blyth for your research.
Yes, thanks to John and Jeff.
Joe Farina wrote:Note: As I recall, Jeff had mentioned to me that potassium metabisulfite should probably work in a similar way compared to the sodium. There are many types of "alum" but I would suggest trying the Aluminum Sulfate first.
[/quote]

Uh, so far I manage to make Sodium Aluminum Sulfate (etched aluminum in H2SO4, then neutralized excess with NaOH, so that final pH is around 3.5). Now, I am about to use different approach: first making aluminum hydroxide by immersing some aluminum foil in 25% ammonia solution, then later will mix it with H2SO4.

That is because I gave up of searching for aluminum sulfate in my town. Did not find anything useful. Only Potassium Aluminum Sulfate, which is similar what I got, but with Sodium instead Potassium.

Best--
milan

Joe Farina
Posts: 724
Joined: Wed Jan 07, 2015 2:10 pm

Milkyness in dcg

Post by Joe Farina » Sun Feb 24, 2013 9:38 am

MilanKarakas wrote:
Joe Farina wrote:Before use, I mix equal volumes of 1 and 2, and soak the exposed plate for about 2 minutes.
I suppose after use, it should be disposed? It can't be stored for late use?
I guess it can be used in the same way as Kodak rapid fixer with hardener. It doesn't need to be disposed right away, I use 200ml of the mixed solution for a full day's work. I don't know its keeping properties exactly. In my case, it clears the dyes in about 1 minute with agitation, and I suppose the small amount of unreduced chromate in the film gets washed into the solution, and this extra bit of chromate (or a lot more dichromate in your case) would help to promote some extra bias hardening (in addition to the hardening taking place due to the alum). I keep the sulfite and alum separate, because the concentrations can be easily adjusted before mixing them together. Also, the Kodak rapid fixer has the hardener separate, and this hardener is mostly aluminum sulfate. I wonder if there is a chemical reason why the hardener is kept separate in the Kodak material, of if it's just because it's easier to adjust hardener concentration that way?

MilanKarakas

Milkyness in dcg

Post by MilanKarakas » Tue Feb 26, 2013 8:34 pm

Hi.

Yesterday tested homemade hardener. It consist potassium metabisulfite (K2S2O5), 1 % water solution, and 0.2% water solution of sodium aluminum sulfate (currently can't find aluminum sulfate alone, so I made my own version).

Seems that thing works, just need to make new batch of the plates, since I did not put old plates in the refrigerator and aside losing sensitivity, emulsion collected various stuff on it (bacteria, mold....).

Even after hardening, some milkiness remains, but much less than after light fixing. Only exception is fixing by heat, where plates are crystal clear, but also with no hologram on it.

Potassium metabisulfite working good, at first it clears yellow tinge in about 15 seconds, but after many plates this time is prolonged to about 30 seconds or so. Not sure how hardener really works, and even not sure whether it is worth to try it on old plates (I wish I can make new batch of the plates right now, but today cut my thumb with axle while splitting wood, so can't wear latex gloves).

Here is some result for comparison:
Comparison light vs chemical hardening.jpg
Light fixed plate on the left, and two chemically fixed plate to the right.
Note that at first hologram nothing is visible, that is because I am trying to record deep scene, which this time failed badly. On the right, two holograms, 4 minutes exposure each, part of the dice stack is not visible. Hologram is illuminated from the side, and both holograms are actually rotated 90 degrees. Stack of the dices shrinking during recording hologram - did not wait long enough so that temperature equalize and linear expansion of the plastic material make it invisible where the cubes move the most.

On next hologram, most of the scene is visible (only part which is deeper is in 'darkness').:
4 minutes exposure plus fixing and hardening.jpg
Relatively good hologram.
But, I tried to make nut more visible and doubled exposure to 8 minutes.:
8 minutes exposure plus fixing and hardening.jpg
Blue shift + stray effects...
Nut is actually at bottom, holding object as close at possible to the emulsion. At certain angle, thread visible, but most of the front is not so visible. (Three transparent spots are due to showing hologram to someone on the rain which just begin to fall, and it is not protected with back plate.)

Aside milkiness, I have additional set of problems with my emulsion: sometimes whole plate is so reflective that resemble golden mirror, but object behind is not visible, or just barely visible:
Mirror like holographic emulsion.jpg
Where light is the most intense, whole emulsion looking like golden mirror, while hologram itself is not visible.
This is another puzzle, and I don't know why this happening. Only i feel that it is somehow related to bad emulsion processing/coating. Or, maybe attempting to get broadband hologram while emulsion is too thick is not possible?

I should play bit more with hardener, seems that it working good, but I am not sure in anything. Next time will separately immerse part of the plates in the fixer and hardener at different duration to see which time of fixing and hardening is the best.

Best wishes,
milan

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MilanKarakas

Milkyness in dcg

Post by MilanKarakas » Wed Feb 27, 2013 4:48 am

Here is some progress. After noticing some difference in heat, light and chemical fixing, decided to try separately fixing and hardening times for the transmission HOE.

And, to my surprise, the highest DE and the clearest part of the hologram is not that fixed too long time, but just 30 seconds. No fixing, very milky hologram. Too long fixing, DE decreases. This time I am not sure whether my formula for the hardening working properly, since somewhat better result got after 60 seconds of the hardening. It will be helpful if someone can tell me the pH of the hardener (component "B").

Sorry for the damage... it is done by using tweezers.:
Fixing and hardening times.jpg
Fixing is obvious, while hardening not so.
At different angle, it is slightly better visible that emulsion become.... different - more relief on the surface and more diffraction efficiency:
Just right fixing time.jpg
Stripe in the middle looking differently.
And, that central part is really bright when light is diffracted through:
It is really really bright.jpg
I am surprised how it is bright.
And, to compare brightness with fluorescent lamp (diffuse light source):
DE vs fluorescent lamp.jpg
Glowing almost brightest than fluorescent lamp. :D
Diffraction efficiency of this HOE is so good, that I wish to make my own rainbow "projector":
Rainbow HOE.jpg
Really nice rainbow on flash lamp.
I am very pleased with this chemical fixing/hardening. Just need to find the right amount of hardener, or right time, or perhaps I do too high pH (around 4) of the hardener (sodium aluminum sulfate, my own messing with the chemistry). Next time will try add drop or two of the sulfuric acid to the hardener to see whether I did make mistake by neutralizing excess of the H2SO4 by NaOH.


Thank you all for your help. I hope my next batch of the plates will look completely different.

Best--
milan

Tony DCG
Posts: 147
Joined: Thu Jan 08, 2015 1:47 pm

Milkyness in dcg

Post by Tony DCG » Thu Feb 28, 2013 10:47 am

MilanKarakas wrote:And, to my surprise, the highest DE and the clearest part of the hologram is not that fixed too long time, but just 30 seconds. No fixing, very milky hologram. Too long fixing, DE decreases. This time I am not sure whether my formula for the hardening working properly, since somewhat better result got after 60 seconds of the hardening. It will be helpful if someone can tell me the pH of the hardener (component "B").
Excellent job milan! This is great work.

I think IMO that you should have gone further in you fix time. You still have not reached a clear state, so you may want to concider 1-3-5 minutes as well. My feeling which I stated earlier is you gelatin is too soft and therefore you may have to undergo great measures in processing to compensate for it. Even if the gelatin is marked as say 220 bloom, it still may not work. In making broadband film, the gelatin undergoes the most stress since you are swelling the film then rapidly shinking it. The gelatin strings or coils snap under the stress which results in whitening.

Many years ago John P saved me from this problem. I brought gelatin that he had used with the same bloom strength, same manufacture, same animal. I tryed tons of things, always white. Then I think he suggested buying some knox gelatin and everything clicked.

Best of luck
Tony

MilanKarakas

Milkyness in dcg

Post by MilanKarakas » Fri Mar 01, 2013 9:58 am

Tony DCG wrote:
MilanKarakas wrote:And, to my surprise, the highest DE and the clearest part of the hologram is not that fixed too long time, but just 30 seconds. No fixing, very milky hologram. Too long fixing, DE decreases. This time I am not sure whether my formula for the hardening working properly, since somewhat better result got after 60 seconds of the hardening. It will be helpful if someone can tell me the pH of the hardener (component "B").
Excellent job milan! This is great work.
Thanks, Tony.
Tony DCG wrote:I think IMO that you should have gone further in you fix time. You still have not reached a clear state, so you may want to concider 1-3-5 minutes as well. My feeling which I stated earlier is you gelatin is too soft and therefore you may have to undergo great measures in processing to compensate for it. Even if the gelatin is marked as say 220 bloom, it still may not work. In making broadband film, the gelatin undergoes the most stress since you are swelling the film then rapidly shinking it. The gelatin strings or coils snap under the stress which results in whitening.
Now, I will try to make another batch of the plates, but this time will use the same gelatin, and different methods. Will leave one plate in humid area, while another one in refrigerator for about 15 hours or so. Just to see the difference.

After this test, I will try photographic gelatin (Thanks to Jean Dufrasne, who provided me this gelatin, 220 Bloom). Before using photographic gelatin, I want to be sure that the process of gelling itself is correct, or at least to see how it behave in different conditions.
Tony DCG wrote:Many years ago John P saved me from this problem. I brought gelatin that he had used with the same bloom strength, same manufacture, same animal. I tryed tons of things, always white. Then I think he suggested buying some knox gelatin and everything clicked.
Yes, seems that I have this problem too. I asked people who manufacturing Dolcela gelatin about Bloom, but got negative answer: "Everything you should to know about this gelatin is already written on the package". Oh, well...

Somewhat different set of problems I have with Dr. Oetker gelatin.

Yesterday tried to make one 'humid box' with hot water tray and fixation for the plates. It is plastic bread box.:
wet box-1.jpg
Bread box with hot water trays and test glass plates.
I just wanted to be sure that there is no condensation on upper surface, while humidity is pretty high (over 85% measured). As temperature goes down, humidity will goes dow slowly as well.

The same box closed:
wet box-2.jpg
Bread box when closed.
It can hold high humidity inside box as long as laminar flow is turned off. Once I want to pull out the plates, but so that humidity goes slowly down, then just run air flow. Condensation on the bottom of the plates will be wiped out somehow. My greatest fear is that plate will accidentally fall into water, as is case in the test (right plate on first photo).

Prior to making real plates, I will do additional test of the temperature and humidity over the longer period. Temperature monitoring is relatively easy, since I have 'remote sensor' for temp. but not for humidity. Only hygrometer which can show me maximum and minimum values _after_ whole process.

Another plate will just put into refrigerator at about 5C for 12-15 hours, and then compare that two ways of the gelling systems.
Tony DCG wrote:Best of luck
Tony
Best wishes,
milan
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Tony DCG
Posts: 147
Joined: Thu Jan 08, 2015 1:47 pm

Milkyness in dcg

Post by Tony DCG » Fri Mar 01, 2013 10:32 am

MilanKarakas wrote:I just wanted to be sure that there is no condensation on upper surface, while humidity is pretty high (over 85% measured). As temperature goes down, humidity will goes dow slowly as well.
I would be surprised if this works. That is some very high humdity. I'm not sure what you wish to accomplish in trying this but it could be interesting.

If you look at the great centers of DCG like Utah, New Mexico (USA) where they mass produce DCG, the humidity is very low. This can be argued of coarse but I think ideally you want low RH to dry film. Now if you wish to have your film more sensitive meaning less exposure time, then you can shoot in high temperature and high humidity. I've have heard theroies as to why that is but basiclly it comes down to control. Film stores longer in a low RH low temp environment. Anyway, no matter. It is great you are trying things out. You will adopt your own ideas based on experiements and in the end you will be better for it.

I'm happy you are trying a different gelatin. That's where my money is. I will again offer some of mine if you would like. I again say this so that you can minimize the amount of variables you have. If you have know good gelatin, you look at other parts of your process if the problem persist.

As always, best of luck and thanks for posting!

Dinesh

Milkyness in dcg

Post by Dinesh » Fri Mar 01, 2013 1:50 pm

Tony DCG wrote:If you look at the great centers of DCG like Utah, New Mexico (USA) where they mass produce DCG, the humidity is very low.
Great centers, huh? You got something against San Diego?! ;) We mass produce DCG too, you know.

Tony DCG
Posts: 147
Joined: Thu Jan 08, 2015 1:47 pm

Milkyness in dcg

Post by Tony DCG » Fri Mar 01, 2013 1:53 pm

Dinesh wrote:Great centers, huh? You got something against San Diego?! We mass produce DCG too, you know.
My error Dinesh :)

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