Shel wrote:
> A few times
> recently the term "hold time" has been used to describe the
> ability of a film to hold a good image after exposure. This
> time, I'm sure, varies with the emulsion and the conditions in
> which it's stored. So, my questions are these:
There are really two issues here. One is called "ripening" and one is called
"hold time." Ripening is actually a bit of a misnomer, since technically it
pertains to a stage in emulsion-making. What it refers to colloquially is
that films change characteristics as they age; color films change their
color balance, and B&W films lose contrast slightly and get slightly
grainier. All films may fog somewhat with age. Generally we're only
concerned about these effects with chrome films, since the color is going to
be inherent in the material and may not be subjected to a secondary
correction. The only difference between "pro" and "amateur" emulsions of the
same chrome film is that amateur versions are released earlier in the
ripening process and left to complete their aging on the store shelves,
whereas pro films are held until just before they reach specification and
then refigerated to retard further ripening until use.
"Hold time" is one of several terms for the length of time between the
moment of exposure and the chemical reduction treatment (development). At
issue is the ability of the emulsion to retain the coherence of its latent
image over time. Exposed silver halides "migrate" and clump together in the
emulsion after exposure, some more so, some less so, and if the hold time is
long enough, the image may be visibly degraded in terms of edge sharpness,
subtlety of tonal gradation, graininess, and fog (it's one of the effects we
see with old "forgotten" films that come to light in old cameras and are
developed after many years like time capsules).
Refrigeration retards the ripening of the emulsion but it has no effect on
the stability of the latent image, although it might affect color balance.
Different films respond differently to hold times, and latent image
deterioration takes place in more or less distinct stages. Much of the
deterioration takes place in the first hour; I can't recall the other stages
but I seem to remember that a slower process of deterioration begins at
about six hours and continues thereafter.
Since you like to experiment yourself, try this: step outside your front
door with a camera with a motor drive on it and expose three films of the
same daylit scene. Be prepared to come inside and develop the last film you
shoot immediately, within minutes of the time it was shot---the shorter the
better. I've been able to start the developer as little as three minutes
after the film is shot. For the second of the three rolls, wait three days
and then process it identically to the first roll. For the third roll, wait
till, say, August. Don't give it any special storage--let it sit out in the
heat and the air.
The differences may be subtle, but I think you'll see them with most B&W
films. As to whether this is going to make you paranoid about hold times or
reassure you that it doesn't matter is probably a function of what film you
test; either way, the information can be useful. If you want to see
differences that are pretty pronounced, run this same test with Agfa 400 or
P3200, the two films I've found respond least well to long hold times. I
compared two rolls of P3200, one processed immediately and one processed a
year later, and the difference was very pronounced.
There is no quantified data about hold times published that I know of.
Various manufacturers will incorporate it into their recommendations, but
this is usually in generalized language ("process promptly," etc.).
Another reason I like Tri-X is that it shows almost no image deterioration
whether it's developed after six hours or six months. It does look a little
better if processed immediately than if processed after a few days, but the
difference isn't very noticeable.
--Mike
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