What chemical reaction occurs during "pre-sulphiding" / "presulphiding"?

[Michael Wesik]

I was asked this question the other day and I can't find the answer to it anywhere...

Assuming you have an archivally processed silver gelatin print, what chemical reaction occurs when you put it in a sodium sulphide bath before bleaching and further toning? Tim Rudman refers to it as "pre-sulphide."

Is there a conversion to silver sulphide happening?

Thanks in advance!

 

[koraks]

Is there a conversion to silver sulphide happening?

Yes, and the silver sulfide will resist bleaching.

 

[Raghu Kuvempunagar]

What exactly does this accomplish? Is it a kind of split toning where you first do a light sepia toning with sulphide and follow it up with some other toning?

 

[koraks]

Yes, I think that's exactly the purpose. The initial sulfide toning will be only partial leaving the majority of the silver receptive to subsequent toning.