Perhaps I'm nit-picking here, but don't you mean noticeable, and not measurable? And by noticeable I mean by eye. As far as measurable differences, latent image loss tends to be linear, as opposed to curvilinear. As such, a sensitive-enough densitometer would be able to measure loss before it was apparent to the naked eye. I believe that the slope of the line for density vs time simply differs between films, and not necessarily the curvature. That is, under constant environmental conditions, those films which begin to lose their latent images more quickly will continue to lose them at a similar rate. Perhaps this is something that could be better clarified by the APUG crowd.
Believe it or not I chose my words very carefully - as I try to do with almost all my posts. That is why I italicised 'measurable'. I just don't always manage to get my meaning very clear, espeially when trying to be brief. I have a sensitive densitometer, and was trained in sensitometry, the various methods of testing film, and all that stuff by Kodak. If it is done carefully enough, and with better equipment than I have at hand, you can measure latent image loss after about five minutes. I did make an unwritten assumption that any immediate latent image loss is neglected for my comments on Kodachrome and Tri-X. In a strict sense you are correct that measurable latent image loss is almost immediate, but I'm not sure that that is of practical importance. I was trying to distinguish between those films that showed easily measurable loss, but no noticeable loss; and the films that showed no significant loss whether measurable or noticeable.
As I mentioned, latent image loss tends to hit the latent image sites with the fewest silver atoms first. From what I have observed, the rate of latent image loss appears to decrease with time, so you may be able to measure, or even see, the difference between a film developed within a day or less and one delayed by a month, but there will be little change between one developed after a month and one developed after three months. It varies a lot from film to film.
The clusters of silver atoms that are small enough to be at the limit of developability are not very stable. Many factors affect the stability of the latent image centres, including whether or not the latent image centre is superficial or internal, and whether it was created by an excited dye molecule or not (ie the wavelength has an effect - the presence of a dye molecule with a positive hole tends to be a bad thing, because 'Dye+' can get an electron back from a silver atom). This whole stability issue is also related to reciprocity failure and latensification by low intensity light. I won't mention Tani's proof of Lowe's hypothesis for the behaviour of positive holes in the presence of R centres, because this is a family forum.
I'm happy to explain my comparatively limited understanding of all this (limited in comparison to real emulsion engineers like PE/RM) further, if you or anyone else is interested.
Best,
Helen
![[No title]](/data/xfmg/thumbnail/34/34060-c81fb16d207094738be9b89a70ae1331.jpg?1734164477)
