Troubleshooting emulsion flaking off during development

[Nodda Duma]

Much to my dismay, my latest batch of dry plates have consistently failed in preventing the emulsion from peeling or flaking off the glass during development. The only one that did make it was a picture of my daughter (which I posted in the media section), but even it was failing miserably.

Prior to this batch, I thought I had solved this problem by controlling temperature, using hardening fixer, and scrubbing the heck out of the glass plates with rottenstone prior to coating. Now I could very well have gotten sloppy or careless with this set, but I'd like to think that I didn't. So I'm confused as to what might be causing the problem.

During development (Dil A HC-110 -- what I've used for all dry plates), the emulsion "flakes" away in ~2-3 mm sized flakes. It continues to flake away during water stop bath and during hardening. In the photo below, I tested in 68F water (same temp as the plate) to verify it wasn't a developer issue and also photograph the phenomena. Note that there is thin layer of emulsion retained on the glass (swiped with my fingerprint).

When I had adherence issues in the past, the emulsion would peel away in large sections. This is the first time I've seen it exhibited in this manner (it's been consistent on every plate), and it's throwing me off.

From what I've learned during my dive into making my own emulsion, the usual suspects for reticulation are:

Temperature
-- All chemicals and water verified at 68C
Not-clean glass
-- I scrub the glass with rottenstone until the water sheets off. Then I coat. This has worked fine in the past.

More pertinent information:

- I mixed this emulsion in November 2015 using the unblinkingeye.com recipe. So a very basic recipe but the emulsion is getting long in the tooth (~5 months stored in the refrigerator). Examples of photographs using this emulsion are posted in the media section, so it has worked fine in the past.

- I divided that emulsion into three containers for storage in the fridge.

- This coating session was from the final container, and was the first time I reheated the emulsion from this container to coat glass. Does age of the emulsion before coating come into play? Does the gelatin not hold up as well under stress of development?

- During this coating session, I sped up the drying time from what I had done prior by aiming a fan at the plates on their drying racks, rather than just let them air dry without circulation. Could this have "stressed" the gelatin excessively, which showed up as cracking after it was softened in the developer / water?



So the obvious answer might be I got lazy when prepping the glass, but assuming I was very careful (and a thin layer of emulsion seems to remain adhered to the glass), and knowing that I control temperature very tightly during development ... is there something else that would cause this problem?

Thanks,
Jason

 

[dwross]

Jason,
I've never seen or heard of this problem, and since I thought I'd experienced just about everything that can go awry, I think your idea that the age of the emulsion is the culprit is probably correct. I've also never let an emulsion get more than two weeks old. Gelatin is a protein. Proteins break down over time. It's easy to imagine that's what happened to your emulsion. Looks broken to me!

Make a new emulsion and coat it soon after making. The coated and dried plates will last a very long time. Time and effort are every bit as valuable as a few grams of silver .

As an aside, here's a link to some useful old documents. "Faults in Negatives" might be an interesting read to you. http://www.thelightfarm.com/Map/Booklets/BookletsPart1.htm

 

[Photo Engineer]

The fact that you have discrete flecks of emulsion indicates some degree of hardening in order that the flakes remain coherent. It could be age or it could be mold or bacteria growing in the emulsion.

Try using a prehardener of 5% Chrome Alum, followed by a 5 minute wash before development.

I do not have any other suggestions for old emulsion but I do recommend that you change from HC110 to D76. HC110 is not very good on poorly hardened emulsions due to the organics and polymers present that allow it to be a concentrated liquid.

 

[Nodda Duma]

Thanks for the replies. My other hypothesis is that I dried the plates too quickly causing stress in the dried emulsion.


Denise: I was limited by the number of glass plates available for coating. Or conversely I made about a quart of emulsion. I can probably just make less next time. My wife would probably disown me if I ordered enough glass plates to completely use a full batch.

Ron I'll try the chrome alum pre-hardener and wash and if that doesn't work then I'll just have to toss this batch and make a new one. I have very old D-76 so I will try that as well.

 

[Nodda Duma]

Tested Chrome alum pre-hardener suggestion:


It didn't hold the emulsion together. I have a 5% chrome alum solution with a bunch of emulsion flakes swirling around.

I'll reheat and carefully recoat one or two plates just to verify that the emulsion is "spoiled", but I'll probably assume that refrigerated not-dried basic emulsion mixed to the recipe I use only lasts between 4 & 5 months (time between now and prepping last set of plates).

I'll have to adjust the batch size to ensure I use it in that timeframe. I actually used about 3/4 of the batch before this go-around, so it shouldn't be difficult to avoid age-induced wastage.


Good data point. At least I got one good photo out of this set (see my media post).

 

[dwross]

Best of luck with your future emulsions. I hope you post your progress (and pics!) here. Hope springs eternal that APUG can become again the go-to place to learn both emulsion making and making art with your emulsions .
d
(p.s. If glass ever seems too expensive or cumbersome, I'm having great luck and fun making paper negatives. Couldn't be easier or cheaper, and limited only by the max size of puddle pushers, i.e., 11" x 14": not a problem.)

 

[Nodda Duma]

Update on my troubleshooting.

Based on info from PE, my emulsion is very thin (as in low gelatin content). With this in mind, I used the last of the emulsion to prep some more plates last night and paid close attention to how it sets up.

My emulsion sets up on a chilled slab of glass (2" thick by 18" diameter mirror blank that I kept in the fridge), the temperature of which ranged from about 40-55 during the time frame. I'm assuming approximate gelatin percentage could be determined by setting temperature. However, once I took the plates off the emulsion liquified again (66 degrees ambient). Ultimately, for my mixture this means some of the water content must evaporate while the plates are racked (laying flat) for drying, and the gelatin eventually sets up overnight. This particular sub-batch was the only one which behaved like this, indicating additional water may have been introduced into the container at some point.

I also acquired a bottle of Liquid Light as a control to understand "how it's supposed to work". I like how it's supposed to work much better.

So for my next batch I'll pay closer attention to the gelatin content. I just need to acquire some more silver nitrate before I do so.

While doing research I did come across a formula for predicting melted emulsion density based on % of gelatin and emulsion temperature. This was from an old Kodak white paper. I'll post a link when I get back to my desk.

 

[Photo Engineer]

It should not remelt so easily. After all, chill set emulsion can "turn a corner" in a coating machine and go into a warm drying cabinet and not run. (It does sometimes, but that is another sorry story ) You see, if there is the right amount of gelatin and hardener, it should set up and "skin" on both surfaces. The top surface "skins" due to evaporation and the bottom stays cold due to the coating surface.

Do you have a good pycnometer?

PE

 

[Nodda Duma]

No. I used to have a good Baume hydrometer but lost it to the kids by attrition last year.

I have an accurate mass scale, so I could get a reasonable estimate I believe.

 

[Nodda Duma]

I exposed two plates which I had coated last night. They survived development, with really nice contrast that I could see under the safe light. However, by the time (about 5-10 minutes) it took to clear and fix, the emulsion had mostly dissolved away into the fixing bath.

So I think maybe due to age and the lower concentration of gelatin, the emulsion no longer retains its desirable cohesion properties. The "flaking" failure mode may have simply been a precursor to total failure.

The liquid light emulsion plates - which went through the same developing and fixing process - came out perfect, albeit less contrasty due to what looks like overexposure.

When those are dry, I'll scan and share.

 

[Photo Engineer]

You might try a mix of chrome alum and glyoxal.

PE