Dry Plate Characteristic Curve

Nodda Duma · Dec 23, 2018

I generated some characteristic curves for some of my recent batches. Batches 20, 28, and 29 are "production" batches and the equation on the plot shows a gamma of ~0.8 for those. I'm pretty happy with the batch-to-batch consistency. Batch 30 is a test batch to tweak the speed, but seems more to have increased the contrast.

I go into some detail here: https://www.pictoriographica.com/dry-plate-blog

Cheers,
Jason

NedL · Dec 23, 2018

The consistency is impressive.
I've been wondering about spectral sensitivity, which I guess would be much harder to characterize, but I keep noticing how well your photographs render sky.
I wonder if as much bromide was used in the earliest dry plates, or if by the time dry plates were in common use bromide was also common in emulsions.... I don't really have a good sense of the history....

Nodda Duma · Dec 23, 2018

Thanks, Ned. I’ve consistently focused on consistency (so much pun fun), and I’m happy with the results. It cost money for the necessary equipment needed to control the process, and it was certainly worth it.

Bromide, Iodide, and Chloride were all known to combine to form silver halides and were all used at the time (in the early 1880s), depending on the specific formula of course. One of Eder’s early formulas used bromo-iodide, and he talked about the optimal ratios to use.

Spectral sensitivity is trickier, since the color spectrum has to be separated out in a uniform manner, and then projected in a way that the magnitude of the spectral response can be measured. I know how to do it, having worked with the necessary equipment as an optical engineer, but it’s a bit more expensive and for unsensitized bromo-iodide emulsions like mine the spectral response is well known.

MattKing · Dec 23, 2018

Nodda Duma said:
characterization curves

Do you, perhaps, mean "characteristic curves"?
Pedants want to know.
Thanks for these threads. Even us non-emulsion makers find them fascinating.

Nodda Duma · Dec 23, 2018

Ah yes... right jargon. Wrong field

ic-racer · Dec 23, 2018

Over an eight-stop range and nice and straight, pretty impressive!

Nodda Duma · Dec 23, 2018

It keeps going, too. D-max is closer to 3 or 3.5

Nodda Duma · Dec 23, 2018

Image from Batch 30:

Photo Engineer · Dec 23, 2018

Acutally, batch 30 appears to have the curve of a dupe film. This upsweep is used to straighten the toe of a reversal film.

PE

Dry Plate Characteristic Curve

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