"Peper grain" from improper mixing?

[Bokaj14]

Images of my plates with peper grain and my emulsion making setup:


I saw a few posts from a long time ago, especially ones mentioned by PE, stating that "pepper grain" can be caused by improper mixing or by too little or poor-quality gelatin. I was using only 500 RPM with a magnetic stirrer, while many recipes mention even 300 RPM…

Also, my peristaltic pump was dropping silver nitrate drop by drop, and the first few drops formed boba-like clumps that quickly dissolved—as far as I could tell (solution got cloudy).

In my case, I suspect the issue was improper mixing rather than the gelatin.

How much stirring should I be using?
And is it okay to add silver nitrate drop by drop, or should I lower the tubing into the solution or use a different method?

 

[brazile]

It's been quiet around here lately, so I'll take a crack at answering this, despite not being an expert, just a somewhat experienced amateur.

1) PE recommended 300rpm for his recipes, both in the book and in person. I was taught the same when I took courses at GEM. I have found in general that that speed is fine while mixing, precipitating, and ripening, but I often go even slower when preparing to coat. Otherwise sometimes I end up with small bubbles, which are a real annoyance in a coated plate.

2) I don't think "drop by drop" is any kind of issue -- the overall rate is important: slower produces larger crystals (effectively grain) and more speed, faster the opposite. And in his book PE recommends a short "seeding" at the beginning, where a tiny bit of silver nitrate is introduced with a brief pause to form seed silver halide crystals, and then the rest of the silver nitrate is introduced, growing those crystals. One of his recipes suggests starting with a highly diluted part of the silver nitrate solution (take some out, dilute with water, precipitate that, then introduce the rest of the full solution; the added water must be accounted for elsewhere in the recipe) as another means to the same end. I have done the former, but not the latter (yet) and while I can't prove it helped, not having done a strict A/B test, the resulting emulsion was a fairly speedy one for an ordinary photographic emulsion. I'd done a longer ripening as well, so not clear which was responsible, or both (most likely). And a steady stream of added silver is supposed to be better for consistency. But PE worked with peristaltic pumps a bit himself and I know Nick Brandreth at GEM did as well, so I don't think that's intrinsically a problem. I've bought some kit to do so myself, but am used to using a syringe for the process so haven't got around to bothering yet.

3) the issue you may have is that it sounds like you're dropping the silver nitrate from above; not clear how far. I was taught to introduce the silver nitrate to the salted gelatin at a point just beneath the surface of the vortex while the stirrer is working. Perhaps adjusting that will help you.

Are you filtering your emulsion before coating? Using a surfactant or at least some ethanol? These may also help.

Best of luck with your experiments.

 

[Bokaj14]

It's been quiet around here lately, so I'll take a crack at answering this, despite not being an expert, just a somewhat experienced amateur.

1) PE recommended 300rpm for his recipes, both in the book and in person. I was taught the same when I took courses at GEM. I have found in general that that speed is fine while mixing, precipitating, and ripening, but I often go even slower when preparing to coat. Otherwise sometimes I end up with small bubbles, which are a real annoyance in a coated plate.

2) I don't think "drop by drop" is any kind of issue -- the overall rate is important: slower produces larger crystals (effectively grain) and more speed, faster the opposite. And in his book PE recommends a short "seeding" at the beginning, where a tiny bit of silver nitrate is introduced with a brief pause to form seed silver halide crystals, and then the rest of the silver nitrate is introduced, growing those crystals. One of his recipes suggests starting with a highly diluted part of the silver nitrate solution (take some out, dilute with water, precipitate that, then introduce the rest of the full solution; the added water must be accounted for elsewhere in the recipe) as another means to the same end. I have done the former, but not the latter (yet) and while I can't prove it helped, not having done a strict A/B test, the resulting emulsion was a fairly speedy one for an ordinary photographic emulsion. I'd done a longer ripening as well, so not clear which was responsible, or both (most likely). And a steady stream of added silver is supposed to be better for consistency. But PE worked with peristaltic pumps a bit himself and I know Nick Brandreth at GEM did as well, so I don't think that's intrinsically a problem. I've bought some kit to do so myself, but am used to using a syringe for the process so haven't got around to bothering yet.

3) the issue you may have is that it sounds like you're dropping the silver nitrate from above; not clear how far. I was taught to introduce the silver nitrate to the salted gelatin at a point just beneath the surface of the vortex while the stirrer is working. Perhaps adjusting that will help you.

Are you filtering your emulsion before coating? Using a surfactant or at least some ethanol? These may also help.

Best of luck with your experiments.

Thank you for this thorough answer.
3) I am droping it from few centimeters (inch or inch and a half) above surface and first few drops i could se cump. Introducing it under surface would probably really help with that as solution would mix with drop before drop would actualy form at all.
2) For seeding what aproximate percentage of silver do you add at the start? And does that look like just shooting it directly in solution in a few seconds?

 

[Lachlan Young]

I am droping it from few centimeters (inch or inch and a half) above surface and first few drops i could se cump. Introducing it under surface would probably really help with that as solution would mix with drop before drop would actualy form at all

Quoting from Ron's emulsion book: "The tip of the syringe must be at or near the bottom but not touching the stirring bar or other mixer". What it sound like is that you are getting intermittent drops rather than a steady flow (you would also get a steady flow if you simply tipped the AgNO3 in one go, as primitive emulsions did) and that is causing problems.

at least some ethanol

Probably best not to use that with a silver bromide emulsion.

 

[Bokaj14]

"The tip of the syringe must be at or near the bottom but not touching the stirring bar or other mixer". What it sound like is that you are getting intermittent drops rather than a steady flow

That is probably my problem yes. Thanks. My peristaltic pump is not making completly steady flow but average is very consistent, I would like to add it slowly and consistent with a pump as I would like to make emulsion of higher speeds. Lovering pumps tube under surface would hopefuly fix pepper grain.

 

[brazile]

Probably best not to use that with a silver bromide emulsion.

I'd appreciate it if you'd elaborate on this a bit. I was taught to do this in my courses, including one that Ron helped Nick and Mark at GEM develop (Ron also visited the second course, which taught his and Nick's bromide-only emulsion) and the instructions explicitly include an addition of about 5ml of 95% ethanol as a surfactant in the finals. I have done hundreds of plates at this point with no obvious (to me) ill effects so long as I let the emulsion stir and incorporate the ethanol long enough -- a few minutes -- but if switching to PhotoFlo would be a real help I'd like to know about it.

I am aware that Ron appeared to prefer Triton X or PhotoFlo 200 as they apparently have some acceleration effects (see p. 66 and Fig 72 and 73), but lists Ethyl Alcohol as one of the surfactants on p. 65 of his book. As I have been using it for both bromide and broom-iodide emulsions (MO1880 and what Mark now calls RM1900) I'd like to understand your point of view.

 

[Lachlan Young]

I'd appreciate it if you'd elaborate on this a bit. I was taught to do this in my courses, including one that Ron helped Nick and Mark at GEM develop (Ron also visited the second course, which taught his and Nick's bromide-only emulsion) and the instructions explicitly include an addition of about 5ml of 95% ethanol as a surfactant in the finals. I have done hundreds of plates at this point with no obvious (to me) ill effects so long as I let the emulsion stir and incorporate the ethanol long enough -- a few minutes -- but if switching to PhotoFlo would be a real help I'd like to know about it.

I am aware that Ron appeared to prefer Triton X or PhotoFlo 200 as they apparently have some acceleration effects (see p. 66 and Fig 72 and 73), but lists Ethyl Alcohol as one of the surfactants on p. 65 of his book. As I have been using it for both bromide and broom-iodide emulsions (MO1880 and what Mark now calls RM1900) I'd like to understand your point of view.

For some reason I recalled it was a specific risk with bromide emulsions and less so with chloride, but here's a link to Ron's comments on it:

Alcohol

I note that many emulsion recipes call for the use of alcohol. Those in the US cheerfully buy "Everclear". In the UK such things are restricted. I have been using isopropyl with commercially available emulsions for coating and have had no problems. Can this be used more generally in the...

www.photrio.com

AKA not worth the risks if safer (and potentially more useful) surfactants are available.

 

[brazile]

For some reason I recalled it was a specific risk with bromide emulsions and less so with chloride, but here's a link to Ron's comments on it:

Alcohol

I note that many emulsion recipes call for the use of alcohol. Those in the US cheerfully buy "Everclear". In the UK such things are restricted. I have been using isopropyl with commercially available emulsions for coating and have had no problems. Can this be used more generally in the...

www.photrio.com

AKA not worth the risks if safer (and potentially more useful) surfactants are available.

Thanks very much! That's fascinating, I must have missed that thread back then (I did my first course in 2014, then a follow-on a few years later). I wonder that he didn't suggest alternatives in the 2nd course that he contributed to, but I can think of reasons why that might be. He certainly was a delight to talk to, and is much missed.

That said, adding small amounts (5ml) of ethanol to an entire batch of emulsion (usually at least 200g or so in my case), seems a small enough risk to me. But I've been meaning to try the Triton and PhotoFlo suggestions anyway to see how they did. If they produce nice effects, I'll likely switch and get both benefits.

 

[Bokaj14]

his book PE recommends a short "seeding" at the beginning

Do you have PEs book? Can you send me PM as I can't as I don't have 20 posts jet?
Also for seeding do you know how much silver do you add and how long I should wait till I continue with the rest?

 

[Bokaj14]

Peper grain on new emulsion:

Now even crazier peper grain, changes that I have maid from last emulsion (while speed is stop or two lower):

- seeding (5% of silver solution for 5 minutes before started addition of other silver)
- different photo gelatin vendor
- perastaltic pumps tube under emulsion surface (so no more droping silver drop by drop)
- a bit more KI (now at 6,5%)
- silver addition now 19 minutes (on top of 5min) compared to previus 9minutes.

I know that making so many changes makes it almost imposible to determine problem.... but what could it be?