View Full Version : Metrics on Azo type emulsions

Photo Engineer
05-27-2008, 04:58 PM
Well, I have finally had time to measure the sensitometric response of my Azo type emulsions against the real thing.

The curves attached have the correct speed relationships to the Azo type paper, that is, my speed goes up with contrast but the lower contrast levels are either identical to or just slightly faster than the original Azo. This is a normal function of my Azo type paper emulsion. So, the fastest emulsion is about 2 stops faster than Azo and the lowest is identical in speed.

The black curve is the Azo - Grade 3 glossy reference. I have compared it with the published specification by Kodak and they match within a tiny line width.

The red curve is the soft grade that was sent out to several people for testing. (I have backed the formula off for speed in this test so it is close to a grade 2 and at approximately the same speed.)

The cyan and yellow curves are two variations on a higher contrast which I would call Hard grade (about 4 and 5). I can achieve even higher contrast, but at the expense of Dmin.

All of these emulsions are repeatable to within less than 1/2 stop in speed and within experimental error give the same curves. In fact, the emulsions are so close that I am now making 500 gram batches and blending them with no problem. The raw emulsion keeps for over 6 months and the coated paper seems to be like the original Azo for keeping - very stable. I use my own paper up too fast to do all of the necessary tests. There are some glitches yet, but almost everything is worked out now.

I have made essentially all grades in between those in the graph. In fact, the Medium grade which I sent out to some of you for testing lies between the 3 experiments in this test and is not shown.

Exposure was 2", development was 1' in Liquidol 1:9 (with virtually identical results with Dektol 1:3), rinse, Fix (KRLF, TF-4 and Super Universal Fix were used with identical results). One artifact is due to my plotting program running the curves back to zero. The Dmin is actually about 0.10. All coatings were on baryta, coated with a 0.005" undercut at 12 ml / foot square. Coating temperature was 110 F onto a cold plate to prevent wrinkles and hardener was glyoxal. Coatings were done at 2 orientations of paper to check response to the paper fibre direction, and coating sizes were from 4x5 to 11x14. The tests here were from 8x10 sheets cut to size. Drying time was greater than 4 hours.

All chemicals and support came from the Photographers Formulary.

More to come as soon as I can do the rest of this arduous work! It keeps me out of the darkroom. :(


05-27-2008, 08:47 PM
Congratulations, Ron. It sounds like you had a productive and successful time in Montana.

Photo Engineer
05-27-2008, 08:53 PM
Thanks Denise, but it was about 50:50, home and Formulary.


05-28-2008, 08:40 PM
Very impressive! Congratulations.


Daniel Grenier
05-29-2008, 05:55 AM
Impressive.You ought to pass this on to Michael Smith and whoever is attempting to replace AZO for him. Even better, maybe he can hire you.