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Rules of emulsion making

Photo Engineer

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APUGGERs interested;

I am still getting comments and questions about emulsion making so here are some rules.

1. Up in temperature, coarser in grain and higher in speed.

2. Down in gelatin, coarser in grain and higher in speed.

3. Up in addition rate, slower in speed and higher in contrast.

4. Down in addition rate, higher in speed and lower in contrast.

5 PA gelatin gives finer grain than photograde gelain.

6. Larger grain or higher iodide gives higher speed.

I hope this helps answer the load of questions I've gotten.

PE
 
Interesting can of worms you seem to own.

In continued appreciation.

Richard
 
No big surprises there - for one who has previously studied crystal growth and nucleation rates.
 
Kirk Keyes said:
Any ideas why?
Click to expand...

Kirk;

I really don't know. I know it as a 'fact' but never asked and since I didn't use it routinely, it was never a prominent 'fixture' in my thoughts. Just the fact that this took place meant that an emulsion made in PA gel required an adjustment in temperature to compensate, and that was evidence enough.

PE
 
Ian Grant said:
And of course time and temperature of both the first digestion and then the ripening stage are equally critical

Ian
Click to expand...

Ian;

Yes, and you might also include the addition rate of the ingredients during the growth stage and what type of rate you are using, linear or quadratic. You would also have to add the type of agent used for soluabilization in the digest etc. etc. So, I went for the KISS principle.

I should add that we distinguish ripening and digestion as follows:

Ripening is a change in crystal size, shape or habit with no added chemistry and basically relies on the soluability of the crystals already formed, and the halide salts present.

Digestion is just as above, but relies on an externally added silver halide solvent such as ammonia.

Both can go on at the same time, but only Ripening is an integral part of a precipitation. Digestion is initiated by an external addition.

As given then, the OP applies to simple SR (single run) or RS (run salt and silver) emulsions, and to their initial condition. To add all of the other factors that I began listing above in this post would further compound the confusion.

Suffice it to say, if all else is held constant and you apply that list to a given emulsion's initial condition, you will see the effects I have stated.

PE
 
Last edited by a moderator:
#1 and #2 both relate to coarser grain which results in higher speed. #4, slower addition rate, results in higher speed as well, this is due to more time to form larger, more perfect crystals?

With my peristaltic pump, I can go from addition rates of about 3 ml/min (with my current tubing size) on down to about any excruciatingly slow addition rate you can stand to wait for. Is there a practical limit as to how slow the addition rate can be made?
 


Kirk;

You can run the rates as high or low as needed by the formula or as needed related to concentration of the reactants.

A faster emulsion with slower addition is also related to lower contrast. This is due usually to the formation of a more polydisperse emulsion with coarse and fine grains lowering the contrast, but the coarse grained emulsions increase the threshold speed. Of course, digestion and ripening both change this but if all else were constant, this is one way to alter speed and contrast at the same time.

PE
 
Photo Engineer said:
a more polydisperse emulsion with coarse and fine grains lower(s) the contrast
Click to expand...

IOW, given that the characteristic curve is essentially a distribution curve, the wider the range of sizes, the lower the contrast and the shorter the range, the higher the contrast. Or, stated more simply, if all of the crystals were of the same size, you would have an extremely high contrast emulsion that would essentially be a straight, vertical line.

Correct?

Ed
 
Old vs Early new, vs New

Old emulsion technology dumped Silver Nitrate or Silver Nitrate + Ammonia into a pot of active gelatin + a salt mixture. This was heated from 1 hour to 2 days at temperatures from 40 - 90 deg C (the 2 day 90 deg emulsions were called BOILED emulsions). The gelatin was active gelatin and the sulfur sensitization came from the gelatin. There were as many as 3 grades of gelatin for this type of treatment. The wash was essentially the last step.

In the 40s - 60s, the gelatin was inactive, and the addition rate was timed at a given speed. Temperatures were 40 - 60 deg C, and sulfur sensititization or sulfur + gold took place after the wash was complete.

After the 60s, emulsions used inactive gelatin, precise flow rates, measured vAg, and precise steps for digestion, ripening, and other addition steps. I have given the steps elsewhere but I include them below:

1. Nuceation - the preparation of the small seeds on which the emulsion is built.

2. Ripening and dilution - the step at which an emulsion is diluted to the optimum gelatin content and vAg. It is held to adjust grain size and composition. *

3. Digestion - the step at which a silver halide solvent is added to modify crystal shape and size. It is held to allow this to take place. *

4. Growth - the step at which more silver and salt are added in a linear or quadratic fashion. Any modifiers may be added here.

5. Hmmm, IDK what to call this, but here the vAg is adjusted by adding silver and salt to the optimum point for grain size, halide content and vAg.

6. Wash

7. Sulfur or sulfur + gold sensitization.

* = optional step.

I hope this clarifies how complex things can be (as if adding complexity can clarify anything )

PE
 
When was the technique of controlling pAg introduced?

Ed
 
Well Ed, that is difficult to say.

When Kodak began making dual run (salt + silver), those were in the 40s and they were controlled by hand to give identical (or nearly so) flow rates. Later a conductivity meter was added and the salt flow was adjusted to keep the needle centered. Then they found that it was a property of the halide, and they worked with pAg, but it was not accurate enough and finally they went to full control and used vAg. This process took place over 30 years, and involved designing several versions of lab and production equipment, each one better than the last.

It was a slow gradual evolution that slowed down in the 90s with the final EK models and automation. I am given to understand that Agfa never completed their automation, and IDK about Fuji or Ilford.

PE
 
Photo Engineer said:
Well Ed, that is difficult to say.
Click to expand...

Thanks. I understand. I'm always interested in those 'ah ha!' moments. Like sitting under an apple tree watching an apple fall or standing on a London street corner and suddenly realizing one could make a fission bomb...
 
emulsion making and gold leaf

have anyone used hand-applied emulsion on gold leaf? I'm looking for suggestions and guidance.
 
Jill - I can't help with your quesiton, but posting it in a thread of it's own may help others find your question. There's a "New Thread" button near the top of this page:
(there was a url link here which no longer exists)

Kirk
 
jill metcoff said:
have anyone used hand-applied emulsion on gold leaf? I'm looking for suggestions and guidance.
Click to expand...

You may want to contact my wife, she works with Gold Leaf all the time. You can send questions to me and she can respond. If you do, it would be best to send you email address and she can respond directly to you.

Her website is www.ReverseGlassPainting.com

Note! You cannot reach her via the Toll Free number. Best to email.

Jim
 
So does the concentration of silver added to the salt+gelatin have an effect? In otherwords, If I add 1mol at 10Ml per minute, is that the same as 2 mole at 5ml per minute? or would this change the crystal structure?

It would seem that less concentrated solutions, added at a higher (and probably more controlable rate) would result in a more monodisperse solution.

Is it advisable to "dump" part of the ag at the start of the proccess, to nucleate tiny crystals in solution, then slowly add the remainder to grow the nucleated crystals?
 
The concentration of reactants change the nature of the precipitated silver halide.

The absolute vAg (or pAg depending on equipment) determines the crystal habit (see a previous post with chart for this) and the control of flow rate of Silver + Salt to maintain that starting vAg will control dispersity.

Addition rate determines overall size and crystal dispersity as well. Shorter addition times give more monodispersity and smaller cyrstals, on average. But, it depends.

Older emulsions used initial dumps of silver. In fact, early German translations use the word "gekipped" (tipped or dumped) to describe the initial step of silver addition.

PE
 
So on the chart that shows crystal shape vs. pAg, it states that this is at 70 C, does the temperature also effect grain shape, As in if we do the addition at 40C, do we need to raise or lower pAg for the given crystal shape.
 
As noted elsewhere, temperature affects the size of the crystal and the rate of digestion/ripening.

Salt affects pAg and therefore the crystal habit. The chart is for Bromide.

PE
 
From the Nernst and Debye Huckle equations one can get to the vAg. Here is the pKsp calculation for Bromide ion as a function of Temperature.

brpksp = -12.1258 + 5868.64 / (T + 273.15) + .015953 * (T + 273.15)

The patent is very early work, but useful. The latest was published in the 90s IIRC.

PE
 
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