Emulsion filtration, large particles

[hchapman]

My first crack at emulsion making for glass plate went pretty well except for large particle formation. I'd like to know if this is normal, or if it appears that this is not normal and some variable(s) in my preparation are at fault.
If it is normal, than my filtration conditions need improvement.
This is a "one in a row" problem and I'm gearing up to try again. But I though a quick weigh in from this forum might help steer me in the right direction to move forward.

The particles show in exposed and developed plates. Developed and fixed plates without exposure show some very slight fog, about 0.03, but that is all. So exposure and development are required for the particles to form.

Exposure of the plates at iso ~0.5 and development in stock Dektol for 8' gives a beautiful image with a density range of about 1.8.
I used the Mark Osterman old style slow plate and lantern slide formula from p. 158 of Mowrey's "Photographic Emulsion Making, Coating and Testing" and followed the instructions closely. I am a retired process chemist with experience using gelatin in preparing my own color separation tissues for tricolor carbon printing as well as in using silver nitrate in albumen printing. I think that there are good odds I screwed something up in this emulsion preparation, but I was at least paying attention to what I was doing and understand the materials.
The emulsion was filtered only through a gold coffee filter immediately prior to pouring. I realize now that the filter is pretty coarse and was only able to remove very large chunks.

Sources:
Silver Nitrate and KI from Bostick and Sullivan
Potassium Bromide from Kodak (old stock)
Gelatin from Gelita, photographic bone gelatin #6387
Everclear
No chrome alum or thymol

After the first plate pour the remaining emulsion went into the refrigerator for a couple of days. It was then re-melted for another pour to do filtration testing. Four plates were made for the test:
-unstirred emulsion sampled from the top of the melt to see if the large particles would settle out
-stirred but unfiltered to demonstrate if the large chunks remain
-filtration through 2 layers of muslin. I know this is vague, but it is how I filtered all my emulsion for carbon tissue pouring
-filtration through #2 filter paper (appx. 8 micron) using an Aeropress coffee filter to push the emulsion through the paper

I have a screen shot attached that shows the results of all four pours exposed through a 21 Step Stouffer step wedge. The step wedge step shown is step 11. The stirred control has a ruler in the image showing 1mm graduations. From this the particles in the emulsion measure, very roughly, 65 microns. The settled, unstirred emulsion is clean. My filtrations through muslin and #2 paper helped some but not enough. The specks show in a contact print from the 5x7 plate, and are very visible with naked-eye viewing of the plate.

So, do I need to do a better job with filtration, or are these particle abnormal and is it likely I screwed up the emulsion preparation?

Thank you,
-Harlan

 

[iandvaag]

Looks like pepper grain. There are two primary methods of mitigation that I am aware of:
1) Increasing the rate of stirring during the precipitation or possibly increasing the "evenness" of addition of AgNO3 by some other method. Slowing down the addition may help.
2) Increasing the amount of precipitation gelatin.

 

[138S]

Adding to previous post.

First, from the fibers depicted, clearly you have dust from air that it can fall in the chem during ingredient preparation, in the addition-processing, in the coating operation, in the drying and in the other drying after development.

If you have fibers then for sure you have also tons of minor dust particles...

I use a Honeywell HAP-16200E HEPA air purifier, not only for the emulsion making but also for anything in the darkroom, scanning and manipulation. The smaller the room and the larger the purifier then the sooner the air is clean enough. Also the kind of clothes you wear are important, wear a cap for the head and don't scratch hair/skin. Dust control is critical in this game.


Beyond air dust, you need a toy microscope to find other contamination sources. All what you use is soluble, what is not air dust are impurities in the ingredients.

> Inspect with the microscope(x100 or 200 total, after objective multiplied by the ocular) your water born particles, from now you need microscope slides and coverslips. A "cheap" ($100) reverse osmosis filter is a nice investment in a darkroom, for many situations, from chem preparation to final rinse.

> Inspect gelatin only with water.

> Inspect every ingredient diluted one by one, some ingredients may bring something. You may make a good filtration of the diluted ingredients.

> Take samples with a pipete in each process stage and throw a drop in a microscope slide, cover it with the coverslip inmediately. You have to check well where you take dust.


That troubleshooting worked for me, another potential source could be some rare impurity in an ingredient that precipitates something I cannot understand, but here you are the chemist, you sure would find it better than me.

You also may want a DIY drying cabinet. You may buy a HEPA filtration spare to inject a very small flow of HEPA purified air in the cabinet, a little computer fan may blow on the HEPA filtration. (search amazon: hepa filter part).

 

[hchapman]

Thank you for your analysis and suggestions. I'll increase my stirring rate first, along with introducing air filtration and inspecting my ingredients.
Fingers crossed!
-Harlan

 

[138S]

hmmm... this is about fun, quite a lot of it !!!!

 

[Peter Schrager]

Curious that maybe I'm missing something here
I make my own emulsion for pop prints and dont have any of these issues. Seems way over the top to have to redo and inspect every part of the making. I take no precautions just making most if the emulsion in my kitchen and finishing up in the darkroom to add the silver nitrite and finishing substances. Only wear protective gear. No air filter etc. I was in Jason lane' s prep area where he makes dry plates and saw no air filtration system or other precautionary measures...I would start and order some gelatin from another source
I get mine from artcraft and no have no issues with it.. secondly the heat can be a huge issue
I reheated some emulsion and let it get too hot
Result was a very COARSE GRAIN ON THE PAPER..WATCH YOUR TEMPS.
honestly you dont a microscope to do this work

 

[Lachlan Young]

Looks like pepper grain. There are two primary methods of mitigation that I am aware of:
1) Increasing the rate of stirring during the precipitation or possibly increasing the "evenness" of addition of AgNO3 by some other method. Slowing down the addition may help.
2) Increasing the amount of precipitation gelatin.

I'd agree that it's probably pepper grain - and not other dust etc contamination. I've seen similar faults on late period Efke/ Fotokemika film as their emulsion plant began to fail.

 

[138S]

No air filter etc. I was in Jason lane' s prep area where he makes dry plates and saw no air filtration system or other precautionary measures...

Having a Plate Drying Box with filtered air injection is a wise recommendation.

See Appendix, Plate Drying Box section in the attached M Osterman's doc. Page 15.

Of course a Wood Plate Drying Rack, with the plates vertical may help to not take dust,



but while emulsion settles with the plate in horizontal position there is quite a lot of risk to take dust.

At the end a basic HEPA purifier may cost $40.

In a dry plate manufaturing facility you may simply not see the dust removal tool. Probably that facility has a ventilation system, if you filter the air input you end having a dust free room. Would you sell plates that may have a fibrer in the middle ?

 

[Peter Schrager]

Perhaps Jason will chime in here...he produces the plates...actually has high school kids coating them
Yes he may have a purification system somewhere...

 

[138S]

Peter, I think you are right, he may have it. Me, personally, as a bare low level enthusiast I felt the need to control well dust for dry plate making, so I guess somebody making some business would ensure plates are flawless the most he can.

If you see the OP's posted images show clear dust from fabric fibers, and anyway we all have a long record fighting dust in many stages of the photo process, imagine a 8x10" velvia sheet with a remarkeble fiber casted in the middle, it could be taken when loading the holder or perhaps it was in the bellows. One may remember that pitfall for ever !

 

[Nodda Duma]

Pour through gold mesh coffee filter to filter out larger particles just prior to coating. Set vertically in a rack to dry (I sell wooden drying racks if you need one).

I just have an air filter running in the coating room in the basement. Helps some but it’s definitely not a clean room. Rob Brazile built me a drying box which pulls filtered air through and that seems to have helped.

but TBH this looks more like peppering. For your next batch try stirring a bit more..magnetic stirrer if you want.

 

[hchapman]

I'm pleased to report success on the second Osterman emulsion batch.
I have yet to pour some unfiltered emulsion to see if it is free of the particles to verify the following, but I suspect the particle problem was possibly the silver nitrate. Although the silver nitrate solution as prepared was colorless, slightly hazy, and looked clean through a toy microscope, on filtering through a 1.2 um syringe filter, it turns the filter black (quickly!) and the resulting filtered silver nitrate solution is water clear. So I used the filtered silver nitrate solution in the second emulsion prep. I'll report back again after testing the unfiltered emulsion form the second batch to see if it has the particles or not.
Also, it is likely that the filtration of the first emulsion batch through #2 paper in an Aeropress coffee filter failed, otherwise the particles would have been removed . It turns out the filter paper I'm using is very delicate when wet and it likely tore during the filtration. Since then, I've filtered the first problem batch of emulsion again through #2 paper successfully and it comes out nice and clean. So the Aeropress filtration method seems to work well when one needs to get the little particles out. Hopefully it won't be needed as a general part of the workflow.
The attached image is from the second batch, but the first emulsion batch re-filtered looks the same. The dreamy/sharp quality I think is wonderful.
Please excuse the scrapes, I'm obviously very low on the learning curve for plate handling.
Thank you all again for your help.

 

[Peter Schrager]

bravo..keep working!

 

[138S]

Yeah... this is ! Bravo !!!

Clearly a true chemist is in command. And what a wonderful plate !