Rules of emulsion making

[Photo Engineer]

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

[richard ide]

Interesting can of worms you seem to own.

In continued appreciation.

Richard

[Kirk Keyes]

5 PA gelatin gives finer grain than photograde gelain.

Any ideas why?

[Ian Grant]

And of course time and temperature of both the first digestion and then the ripening stage are equally critical

Ian

[Ole]

No big surprises there - for one who has previously studied crystal growth and nucleation rates.

[Photo Engineer]

Any ideas why?

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

[Photo Engineer]

And of course time and temperature of both the first digestion and then the ripening stage are equally critical

Ian

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

[Kirk Keyes]

#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?

[Photo Engineer]

#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

[Neanderman]

a more polydisperse emulsion with coarse and fine grains lower(s) the contrast

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