[Leica] Tri-X: a technical view

[Erwin Puts <imxputs@knoware.nl>]

The current discussion on the relative or absolute erits ot Tri-X is 
indeed refreshing. So a technical appraisal giving some background 
info might be helpful. Classical emulsions like Tri-X use thicker 
emulsion layers than Tgrain  (modern films). The growth of 
silverhalide in the classical emulsions is less controlled than in 
the tabular controlled grain. Thus the shape of the individual grains 
in the  Tri-X emulsion are more irregular and the size of the grain 
has a wider span. You will find very small sizes and very big ones 
and everything in between. So we have a thicker emulsion and more 
irregularly shaped grain that is distributed over  a larger bandwidth 
of size. If we have larger and smaller grains side by side we 
increase exposure latitude as the small grains are less sensitive 
than the bigger ones. But the shape and size distribution has one 
more effect: it enhances the internal (micro) contrast and promotes 
the recording of subtle tonal differences. Again courtesy by the 
wider latitude in distribution of  grain size and shapes. If we have 
grain clumps in all sizes the chances are quite good that  small 
variations of tonality in small subject areas can be captured more 
easily by this assortment of grain sizes and shapes.
Another point: D76 is a halide solvent type of developer, that 
reduces the grain clumps during development and gives them soft 
edges. This tendency flattens the internal contrast and when used 
with modern (Tgrain) films which inherently are of flatter micro 
contrast, the effect is doubled. That is why the tonal rendition of 
Tmax in D76 is markedly different from that of Tri-X in D76. Another 
often overlooked point is that filmdevelopers function as chemical or 
physical development processes. The difference is a difference in 
grain clumping, but also the silver deposit may be black or sivery. 
Both types of course  reduce the light transmission, but the black 
silver gives a different quality of light than the grey silver.
Of course if you are well versed in the intricacies of these effects 
and the ways of influencing them/compensating them you may use any 
film/developer combination and emulate quite effectively any other 
one. But when you opt for one of two different  strategies/materials 
you end up with intriguing results, which are more predictable if you 
know the basics.


Erwin

Please note: all my articles about technical matters, even when 
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