I started this message as a reply to Ole in the rotary development thread but it is clearly more appropriate here.

In my opinion halation and infectious development are related phenomena in the type of situation described earlier by Aggie.

Halation is light scattering either through the emulsion, or off the base of the film or glass support and back into the emulsion. However, the immediate result of halation is a latent image that is only made visible by the action of a reducer during develoment. For that reason it is correct to veiw these two actions as related since type of develoment can either decrease or increase the effects of halation. So the bottom line is the type of development can actually increase or decrease the effects of halation by limiting the extent of infectious development.

There is some literature which shows that Pyroc developers, which harden the gelatin more than other developers, and thereby establih a barrier to the migratin of silver halides, are more effective than non-hardening developers in redcuing the effects of halation through infectious development. Gordon Hutchings says something about this the his Book of Pyro.

I don't understand why Aggie's friend recommended againt the use of a Pyro developer in the type of situation extreme highlight/shadow situation she described since most of the literature, including Hutchings, suggests that staining/hardening developers actually work better than traditional developers in this type of situation.

Sandy King