Dmax measurements of several papers.

[Photo Engineer]

Agfa Lupex paper was a good example of the use of all of the then-current chemistry to get good black tones using addenda. Brovira was another.

Kodak Azo and Kodabromide were similar in nature to these, but the pure Lupex gave an excellent black tone image with no addenda whatsoever.

PE

 

[sanking]

I was very impressed with the low fog of the 1946 sample. Using the same densitometer and mode the old paper measured only log 0.04 more than the new sample. Frankly I had no idea at the time that any paper that old could have such low B+F so I was pretty shocked when I first did the tests. Since then I have heard from a number of people who have found relatively low B+F levels in very old AZO samples.

Sandy

This is very interesting. Your observation is well in line with the introduction of a very potent and effective antifoggant, 1-phenyl-5-mercaptotetrazole (PMT) for chloride emulsions in late 20s or early 30s. PMT would cool the image hue very much, whether added to the emulsion or developer, so that's why I was curious about the image hue in 1926 version. With that much fog, image fog wouldn't be the same as when the emulsion was fresh, no matter how much BTA or PMT is added to the developer.

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[Ryuji]

What would be also interesting to me is, to strip the emulsion off the 1926 and 1936 emulsions and look at the crystal structures under scanning electron microscopy, and compare that to today's Azo. I don't see much new technology in that area in 1930s but whether today's Azo is made in the same way or not could be argued on a more sound basis.