.
>Newer research (Image Permanence Institute, Rochester and J. S.
> Johnsen, Kopenhagen) showed, that selenium and gold toning is much
> less effective than Ansel Adams and subsequently others (including me)
> thought. IPI therefore developed a polysulfide toner (IPI Silverlock),
> which protects the image much better, without turning the image too
> brown.
Someone at some point (possibly in a state of drunkeness;-)) thought of
removing the gold out of the gold toner and realized that the protective
effect was just as good if not better. The protection did not come from
the gold but from the sulfiding part of the toner. Oh well, so much for
125 years of established photochemistry;-)
Other people thought of refining the "gold toning without gold" to
maximize the level of protection while minimizing the effect on the
image color. They had the protection of microfilms in mind possibly
because of the nature of their research funds.
Luis Nadeau
Paris, France