Longevity of latent image

[Compaq]

Has anyone here done systematic testing of how the "strength" of the latent image reduces with time? I just read the following passage in "Radiochemistry and Nuclear Chemistry" (3rd ed, Choppin et al), which explains in short how film works and how long-lived a "nuclear latent image" is:

......"Nuclear emulsions are similar to optical photographic emulsions. They contain AgBr crystals embedded in gelatine to which small amounts of sensitizing agents have been added. The AgBr content is as much as four times (i.e. 80% AgBr) greater than in optical film. Also the crystals are much smaller (developed grain 0.1 - 0.6 um) and well separated. The emulsions come in thicknesses from a few um up to 1 mm. Nuclear radiation passing through the emulsion causes ionization and excitation which activates the AgBr crystals, producing a latent image of the particle path. Upon development the activated crystals serve as centers for further reduction of silver, leading to visible grains. It is assumed that at least 3 silver atoms must be activated to produce visible grain, while about 30 atoms are needed for normal blackening. Each activated grain seems to require about 2.5 eV to be absorbed on the average.
......While the memory effect of the developed film is almost infinite, this is not the case for the latent image which slowly fades, depending on the number of originally activated silver atoms, the film type and external conditions like temperature, humidity, etc. When stored under ambient conditions, about 80 % of the latent image disappears in half a year."
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So, if photographic latent image shows the same degree of degradation over time, then I really need to start develop my films faster. Has anyone ever done some testing of this? With standardized exposure and development procedures, and equipment to estimate silver density on the negative, it should be possible to see a degradation trend by plotting Ag density as a function of storage time.

 

[tirediron]

I've never done any testing, but I know from experience that I have developed film that was years old (10+) which produced negatives with no apparent degradation (other than that which my lack of skill introduced).

 

[Compaq]

Did you compensate for the long storage by over-developing it, or did you follow the basic instructions as if newly exposed?

 

[tirediron]

I don't seem to recall doing anything special, but I may have had an extra sandwhich during development (FP 4 was normally a 1 1/2 sandwhich process, so I might have gone to two...)

 

[Ysarex]

No controlled testing but I have empirical observations from many years of practice.

As tirediron notes a B&W negative latent image is going to remain present and useable for many years.

My experience tells me that the film develops an overall fog as the latent image degrades but it's a very slow process. I've had people bring me old cameras with 20 year old rolls of B&W film still in the camera and we successfully processed the film to usable results albeit fogged and requiring a corrective contrast boost.

Color film is a different matter in that visible shifts in the color response can be apparent in as little as 3 or 4 weeks if the film is left unprocessed. Still a usable image will be there even years after exposure.

Joe

 

[Derrel]

"about 80 % of the latent image disappears in half a year."

UTTER B.S.!!! I developed a 30 year-old B&W film this May. It has almost no fogging, and the images were very strong. It has been stored in drawers at room temperature since 1984.

 

[Ysarex]

"about 80 % of the latent image disappears in half a year."

UTTER B.S.!!! I developed a 30 year-old B&W film this May. It has almost no fogging, and the images were very strong. It has been stored in drawers at room temperature since 1984.

Isn't somebody out there still finishing up processing Gary Winogrand's undeveloped film?

Joe

 

[compur]

I recently sold some B&W film exposed in the 1950s but unprocessed. I never saw the buyers' processed images from the film but I know they were very pleased with it so I presume they got usable images at least.

 

[PWhite214]

"about 80 % of the latent image disappears in half a year."

UTTER B.S.!!! I developed a 30 year-old B&W film this May. It has almost no fogging, and the images were very strong. It has been stored in drawers at room temperature since 1984.

Please note the image decay rate is for a specialty Nuclear emulsion, not for 'run of the mill' photographic films. It is like comparing oranges and apples. Ilford makes Nuclear emulsions, interesting reading, but a completely different type of film. http://www.ilfordphoto.com/Webfiles/2006214150271441.pdf

I concur with Derrel on standard photo film. It is much more stable

Phil

 

[Josh66]

The general rule is one stop of developing compensation per decade past the expiration date. That really isn't much.
(If it was originally exposed at an ISO of 400 and it is 10 years past the expiration date, you should develop it as if it were exposed at 200 ISO.)

 

[Derrel]

As I recall, some of Admiral Peary's plates from a polar expedition were found, exposed but undeveloped, in the 1980's, having been buried in permafrost for about 80 years, and they developed fine. Not too long ago, I believe in this decade, additional long-term, cold-stored plates were discovered, and modern-day images have been released: I saw some earlier this summer. They looked pretty good. I think some of the newer plates might have been from Frank Hurley Shackleton's cameras.The photographs of Frank Hurley: Shackleton's Antarctic expedition gone wrong.

 

[Josh66]

I don't think the stop-per-decade rule applies to permafrost stored plates, lol. I have developed some ~20 year old film, and that "rule" worked well.