Emulsion seems to react with nitrile gloves.

[Photo Engineer]

I can't answer that Jason. We got some at GEM that were supposedly SS but they began to corrode. Remember that the AgNO3 is highly corrosive.

PE

 

[Nodda Duma]

Yes. This syringe won't ever see AgNO3, only emulsion.

Cheers,
Jason

 

[Photo Engineer]

Ahh, but the tips might.

PE

 

[Nodda Duma]

Quick update: Found another source of swirls. I wasn't waiting long enough for the chrome alum subbing layer (1L H20, 5g gelatin, 0.5 g Chrome Alum) to harden. Rule of thumb seems to be allow to dry and then harden 24 hours. I'm assuming this is the time required for the thin gelatin layer to harden enough that the melting point is above 104F, the temperature at which the melted emulsion is applied when coating. My question is, how far above 104F is the melting point? I'm curious to discern the melting point vs. time relationship. I've scoured the literature to find data on melting point vs. the time that the layer is allowed to harden, but only found Pouradier's paper "Viscosimetric Study of the Hardening of Gelatin by Chrome Alum" and Crabtree and Russell's study of chrome alum stop baths. Pouradier only plots relative hardening (not providing melting point data). I'm still going through Crabtree and Russell's, but I think the stop bath muddies the waters.

So I guess my question is, where to look for gelatin melting point vs. relative hardening data? I can't find any.

I've seen mention of a pure chrome alum wash, which I'm tempted to try. I could also harden the emulsion itself (I like the idea of dipping the plates in thin chrome alum / gelatin bath after emulsion coating has dried, but unsure about fogging over time).

 

[Photo Engineer]

The melting point of raw gelatin is nominally 70F, thus the normal "old fashioned" temperature for processing B&W.

However, the MP of hardened gelatin essentially vanishes. It either reticulates or sluffs off as pieces and parts based on the general cross linked chain lengths.

PE

 

[Nodda Duma]

The chrome alum layer wasn't causing more swirls. Problem is that the silicone from the plungers got into my emulsion jars and contaminated the whole lot. That stuff is impossible to clean off, and while there wasn't much ... it was enough to contaminate the emulsion and cause weaker but still visible swirls. So now I'm in the process of tossing the jars in the trash (along with the approximately half-gallon of emulsion currently stored in them) and acquiring new jars. $#%@! I really despise silicone lubricant!

I did find that adding a small amount of KBr prior to coating as a stabilizer helped reduce the silicone-induced fogging of the swirl effect. It wouldn't go away, but it would be significantly reduced. Another side benefit: While trying to track down correlations with potential causes and doing all the related testing and research, I learned a helluva lot more about details of emulsion making and adding finals than I would have if I had never had this problem (what can I say, I'm an optimist).

 

[Nodda Duma]

So interestingly, I've finally discovered a dry plate made by someone else exhibiting the strange swirly artifact I was seeing in my earlier batches!

https://whystoptime.wordpress.com/tag/dry-plate/

The scan of the portrait exhibits the artifact in the upper corners. In this case, it's an Agfa plate from the mid-1980s, developed in Rodinal, with a thin resulting plate similar to results that my plates would see. These Agfa plates were used for electron microscopy, so I assume a very fine grain similar to my emulsion. The author indicates a belief that the artifact is due to the age of the plates.

Unfortunately, there's no one at Agfa to contact and ask if they know what would cause it.

Very interesting.

-Jason

 

[Michael W]

So interestingly, I've finally discovered a dry plate made by someone else exhibiting the strange swirly artifact I was seeing in my earlier batches!

https://whystoptime.wordpress.com/tag/dry-plate/

The scan of the portrait exhibits the artifact in the upper corners. In this case, it's an Agfa plate from the mid-1980s, developed in Rodinal, with a thin resulting plate similar to results that my plates would see. These Agfa plates were used for electron microscopy, so I assume a very fine grain similar to my emulsion. The author indicates a belief that the artifact is due to the age of the plates.

Unfortunately, there's no one at Agfa to contact and ask if they know what would cause it.

Very interesting.

-Jason

Funnily enough that is my photo that you linked to. I exposed a lot of those Agfa plates from about 2009 to 2015 and sometimes they were clean and sometimes they had all sorts of marks, including swirls - see attached for an extreme version, which also shows black dots of missing emulsion. I've always assumed it was somehow related to how expired they were - about 30 years past their use by date, but I don't know.

 

[Nodda Duma]

Small world! Thanks for posting.. I'm glad I found them because, in a way, it is encouraging to see the issue elsewhere.

The artifact cropped up in my plates when I naively scaled up to larger volumes without compensating for the change in temperature profile due to the greater mass. I presumed that the gelatin content was not sufficient to hold the larger grains and/or created a lack of stability resulting from the longer unadjusted ripening times. My other theory was that something had changed in how I prep the glass, and residual detergent contaminants were causing the issue. Either way, I found that adding stabilizer helps (that and fixing the temperature profile), and perhaps the stabilizer in Agfa's emulsion staved off the swirlies for years.

 

[RauschenOderKorn]

The pattern on the old Agfa plates reminds me of pictures I have seen when materials have been subject to ecessive stress and the structure of the materials changed.
The pattern on the plates of the op look more like some kind of contaminations / demixing / fallout of something which won´t stay in the emulsion or shouldn´t be there in the first place.

 

[Photo Engineer]

Jason, have you cleaned all of the plates using DW after the detergent or chemical cleaner? Is the top plate always clear of defect, and then you see defective plates? If so, this may be an indication of either a contamination or stress (back to front) effect. Kind of like Newton's rings caused by stacking or drying when humid.

PE

 

[Nodda Duma]

Jason, have you cleaned all of the plates using DW after the detergent or chemical cleaner? Is the top plate always clear of defect, and then you see defective plates? If so, this may be an indication of either a contamination or stress (back to front) effect. Kind of like Newton's rings caused by stacking or drying when humid.

PE

To your first question: Yes ... I did find that, when I started getting my daughters to help, they were pulling the plates out of the sonic bath and not getting them into the rinse quickly enough before the detergent (Alconox Alcojet) water would dry out. This left residue that wouldn't rinse off easily, and it is easy to inspect for in incident light. I fixed that problem, ensuring that the plates are clean before applying the subbing layer.

To your second question: The plates are not stacked until fully dry. After subbing they are held in drying racks with ~1" separation between plates for at least a day to allow the subbing layer to harden. As the gelatin dries I have no doubts at all that there is stressed induced in the glass. However, this would induce a mild surface curvature -- probably a couple waves worth, or ~1.2um surface deflection -- to the glass and thus induce optical power, or deviation from flat. Interference fringe effects wouldn't be created. Newton rings require an airgap or other differential index media gap thickness on the order of a few wavelengths of light, which isn't the case here. Stress fringes would show up when viewing incident sunlight with polarized glasses but not under otherwise visible conditions..unless dried emulsion has a polarizing effect.

 

[Photo Engineer]

Hmmm, interesting. Neither Mark, Nick or I have seen this and we use several different methods. One thing we three have in common is that we don't use a subbing layer.

PE

 

[Nodda Duma]

I looked at that, too...extensively. I coated plates with and without subbing layer. There was no correlation.

The biggest correlation was improper scaling of the batch size. When I went back to my original 1L batch size they went away. From there I scaled back up controlling the temperature profile.

 

[Photo Engineer]

OK then. Did you use thick walled beakers or some sort of insulation around the "kettle" when you made the emulsion above about 500 ml? There is a disproportionate heat loss with thin walled or uninsulated kettles above about this value.

There is also a mixing problem above this approximate value wherein you have to use both paddle and magnetic stirrers to get the right agitation during precipitation.

PE

 

[Nodda Duma]

Waterbath temp controlled with a PID, and I have the temperature change for different sized batches characterized. When it’s time to cool down at end of ripening, I can control the rate of change in temp with a chiller system to cool the waterbath. The chiller temp can be set of course, and the rate of temperature change (up to 60C/hour) can be set. So I can replicate for larger batches the temperature profile of a smaller batch very well, a focus of my engineering efforts once I realized this was a critical aspect. In mimicing the temperature profile of a smaller batch, I only deviate by max 1/2 a degree at any point along the temp vs time curve.

The stirrer I use maintains equivalent temperatures throughout the vessel full of emulsion to the best of my ability to measure.

It’s a pretty cool setup, now that I think of it.

 

[Photo Engineer]

Then it is either the stirring uniformity (mixing) and not the temperature distribution. Or, perhaps, the subbing.

PE

 

[Nodda Duma]

*was. I no longer have these artifacts.