Diazo works by hardening and becoming insoluble to the action of a
developer. In many cases, the developer is water. Diazo can be soluble or
insoluble, but not both. Therefore, it is difficult to obtain gradation. A
half tone is made up of small dots that are either black or white,
gradation coming from dot spacing or pitch to use a familiar term. So it is
reasonable to assume that the material works better to create halftones.
Diazo is capable of resolving to extremely fine limits. that is why it was
once used for the production of Integrated circuits where it takes a
microscope to see the details.
RM