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I have done a great deal of BTZS type testing of Pyro negatives. At this point I use mostly Pyrocat-HD, a pyrocatechin/phenidone formula that I developed several years ago and which is now offered as a kit by Photographer's Formulary.
My interest is almost exclusively alternative printing with carbon, kallitype and palladium so my testing would be of limited use to folks who make silver gelatin prints, with the exception of AZO.
For alternative processing, which are primarily sensitive to UV light, I measure the stained negatives with a special densitometer that has a UV measuring tube with greatest sensitivity at 373 nanometers. The results provide me with a very accurate indication of the actual effective printing density of a stained negative with the alternative processes mentioned above.
A reading through the blue channel provides a fairly accurate indication of actual printing density range for AZO papers since the primary sensitivity of this paper is to blue light. Just how accurate I really don't know since I am not doing any actual printing with AZO. However, the time and temperature recommendations I have provided some AZO printers for Pyrocat-HD suggests that the correlation is pretty close.
Since most people don't own UV reading densitometers I am often asked if there is a constant difference they can apply to the blue reading. Unfortunately this is not the case since the stain if proportional to silver density, and as the amount of stain increases so too does the difference between blue and UV readings.
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