Milkyness in dcg

Dichromated Gelatin.
holomaker
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Joined: Wed Jan 07, 2015 8:01 am

Milkyness in dcg

Post by holomaker » Wed Feb 20, 2013 6:37 pm

MilanKarakas wrote:I have different set of issue: milkiness. And something that is not related with process temperature. No matter cold or warm first bath, holograms appear milky. Recently discover that after baking at 100C for 3 to 4 minutes, hologram is much more clear, but also lacking of diffraction efficiency.

Tried light fixing before exposure, light fixing after exposure, tried light fixing at emulsion side, glass side, both... no matter what I do, it is or milky or there is almost nothing on the plate.

And, my last batch of the plates are with too thick emulsion and too much dichromate in it (100:12:3), so for recording at 450 nm, often I am getting terrible UV shifting (I can't say blue shifting, because laser is already blue). Tried to skip 70% alcohol bath in order to get broadband reflection hologram, but what I got is just whole plate broadband, while object is really not visible. Transmission holograms are somewhat okay, probably because emulsion shrinking does less blue shifting. Not sure.


Best wishes,
milan

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holomaker
Posts: 677
Joined: Wed Jan 07, 2015 8:01 am

Milkyness in dcg

Post by holomaker » Wed Feb 20, 2013 6:43 pm

so your coating using veil coating, it sounds like your enviroment is quite dry and its possible your locking in moisture (as the otuside skins over), try enclosing the wet film in a tent with some water/boiling/evaporating allowing the moisture to excape from the bottom for 20 mins or so ............ its usually that or its the hardness factor with light/heat/fix (or even all three)!

MilanKarakas

Milkyness in dcg

Post by MilanKarakas » Wed Feb 20, 2013 7:35 pm

holomaker wrote:so your coating using veil coating, it sounds like your enviroment is quite dry and its possible your locking in moisture (as the otuside skins over), try enclosing the wet film in a tent with some water/boiling/evaporating allowing the moisture to excape from the bottom for 20 mins or so ............ its usually that or its the hardness factor with light/heat/fix (or even all three)!
Yes, that is I am afraid of: upper layer is too dry, while some amount of water is trapped inside. I will try to do as you suggested; making something that will increase humidity.

Also, noticed one thing (maybe it is related to this issue); when plate is aged (about 4-5 days) at 15C and 60% RH, then when scoring glass and it breaks, emulsion tend to stay there. But this last maybe day or two. After that, emulsion breaks easily as it is dried too quickly. Is that 'elasticity' of the emulsion is sign that it is properly aged, and if so, does this mean that I should then put all plates in refrigerator to keep that elasticity until use?

I am not sure my question is clear, so I will rephrase it: when plates are fresh, and when I cut them, I feel no resistance from the emulsion side. But after few days, it behave like thin plastic foil - resisting tearing apart. Is that sign of properly aged film? And, after additional period, such feeling cease, plates separates without any resistance (too dry?).

Best--
milan

holomaker
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Milkyness in dcg

Post by holomaker » Wed Feb 20, 2013 7:42 pm

I see this when im making film and cutting up the dried plate. Try to cut it as soon as it dry on the surface. i slide my Kim wipe across the dry surface , if it slides like skates on ice i know its reay to be cut, if i feel resistance i now it need more drying time ./

MilanKarakas

Milkyness in dcg

Post by MilanKarakas » Wed Feb 20, 2013 7:58 pm

holomaker wrote:I see this when im making film and cutting up the dried plate. Try to cut it as soon as it dry on the surface. i slide my Kim wipe across the dry surface , if it slides like skates on ice i know its reay to be cut, if i feel resistance i now it need more drying time ./
That is so good idea. I think I have problem with so low humidity here because of winter time. Stove heat all water vapor, and since walls are cold, water condenses onto it, so no much vapor remains in the air.

Spring, summer and fall time - somewhat better situation, sometimes too humid. Your idea about making sort of tent (and adding hot water inside to increase humidity) is excellent!

Thank you for this advice. Once I am thinking about that, but afraid that this will lead to dew condensation on the plates, but now I think that this will not happen if plates are warm too.

When doing veil coat, I pre-heated plates to 38C, but since plates are so thin (2 mm), it cools too rapidly, so don't know exact temperature when applying gelatin/dichromate mix. I feel that this part of balance between temperature, humidity and perhaps something else (time?) is the most important.

Also, curing time, or better said 'aging' is important as well. When too fresh, I got milky plate, but this time it behave completely different; diffraction pattern is somewhat visible onto emulsion side, while plate is completely non-transparent. If plates are aged, but initially dried too quickly, then milky plate has hologram on it, to some extent visible through the plate, but looking like object is inside dense fog.

Here is one example, transmission hologram recorded at 450 nm:

http://www.flickr.com/photos/milan_karakas/8479978990/

This hologram is post-exposure hardened by heat, but seems not sufficiently. If such post-hardening is too hot or too long, then got clear plate, but DE is terribly low.

Best--
milan

holomaker
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Joined: Wed Jan 07, 2015 8:01 am

Milkyness in dcg

Post by holomaker » Wed Feb 20, 2013 8:26 pm

Milan did you view my you tube on the veil coating method? It shows a period of time directly after coating ,where i blow/heat the emulsion’s surface? this helps to even the coating on a cooler plate but the blowing must be very weak and brief ..............
http://www.youtube.com/watch?v=b0Toqidt ... w&index=35
Last edited by Anonymous on Wed Feb 20, 2013 9:00 pm, edited 1 time in total.

MilanKarakas

Milkyness in dcg

Post by MilanKarakas » Wed Feb 20, 2013 8:50 pm

holomaker wrote:Milan did you view my you tube on the veil coating method? It shows a period of time directly after coating ,where i blow/heat the emulsion’s surface? this helps to even the coating on a cooler plate but the blowing must be very weak and brief ..............
http://www.youtube.com/watch?v=b0Toqidt ... w&index=35
Wow! You blow heat onto the emulsion? Does it will lead to even worst drying of the surface, while deeper layers will remain still wet? Or, as you said; for brief period it will not hurt the emulsion?

I will try that too very soon (after flu gone).

Thank you for advices above. I will try many things, actually everything to get rid of that annoying milkiness.

Best--
milan

holomaker
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Joined: Wed Jan 07, 2015 8:01 am

Milkyness in dcg

Post by holomaker » Wed Feb 20, 2013 9:04 pm

the brief heat is only to rewarm emultion to allow the gelatin noodles to lay down nicely and noting to do with drying ...........

MilanKarakas

Milkyness in dcg

Post by MilanKarakas » Wed Feb 20, 2013 9:18 pm

holomaker wrote:the brief heat is only to rewarm emultion to allow the gelatin noodles to lay down nicely and noting to do with drying ...........
Oh, that is something new to me. Thank you again.

Best--
milan

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

Milkyness in dcg

Post by Tony DCG » Thu Feb 21, 2013 11:38 am

milan what gelitan are you using again?
A while ago I tryed some 190 bloom strength hoping for some better broadband results but no matter what I did I would get whitening.
holomaker wrote:And, my last batch of the plates are with too thick emulsion and too much dichromate in it (100:12:3), so for recording at 450 nm, often I am getting terrible UV shifting (I can't say blue shifting, because laser is already blue). Tried to skip 70% alcohol bath in order to get broadband reflection hologram, but what I got is just whole plate broadband, while object is really not visible.
Sounds like you have a lot of issues you need to sort out. IMO I would reccomend a systematic approuch. Examples:
If you are unsure about coating thickness, try a veil coating, apply as normal but allow it to sit vertical for say 1 minute. This will give you a thinner coating on top and thick one the bottom. Cut film into strips horizantally so you can have a good sample of thicknesses. Looking at your ratios 100:12:3 you should be fine. In fact for BB you could go up to 6 AmDi.

You can the mask your laser light and vary your exposure time. Go big something like your nominal time (say 1 minute). Try 30 seconds, 1 minutes, 2 minutes, 3 minutes.

Then with either with light fixing or with chemicals exposure you can vary fix time ie mask a third of the plate, light fix it, the exposure the next third (along with the first third) etc. This will bracket your fix time.

Lastly you can vary your IPA %s as well if you wish.

As far as environment, invest in a cheap humidifier. Try to acheive 40-50% RH and stay around 70-75'F in room temperature. Try to eliminate that variable. This is for coating and shooting.

This can be done with one (maybe 2) large 11"x9"" plate and should get you in the ballpark as far as parameters. It would be great to publish these results to the forum and allow us to verify you are getting expect results.

I think every DCG newie should go though this process. Then make good notes, seal the plates and use it as you change your process.
Just my thoughts :)
Good luck!!

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