During a Tillman Crane workshop in pt/pd printing we suddenly got strange fogging. The problem seemed to be the combination of pt and Na2. Here's a quote from a post in another forum written by Tillman after he's done some testing.

"My conclusions are these:
Although I used the PT/PD/and NA2 combinations for a long time with
little to no problems I would not suggest using traditional PT and NA2
in the same emulsion. I was using NA2 at 5% and in very small
quantities. i think that the amount of NA2 effects the staining we saw
on the prints at the workshop. In essence I was using such a small
amount of NA2 in my emulsions the problem did not show up. But using
even one drop of NA2 in 12 drop of emulsion created the fogging effect.
So my suggestions are
1. Use the traditional contrast methods FO#1 and FO#2 and PT/ PD for
negs that are pretty contrasty.
2. Use the NA2 method for any negatives that require more then 3-3 -3-3
3. If you want to only use the NA2 method, dilute the NA2 to a 5% or a
10% solution and use 6-0-6-0 and what ever NA2 is called for."

I don't know if this fogging is a problem with just some papers or all. We used Arches plantin and Cranes kid finish at the work shop.
FWIW Dick Arentz does not have any pt in his solutions at where he describes the Na2 method.