[Mark Layne]

And yet..the "look" of the prints are radically different between Portriga and Brovira of the same period..also the keeping and ageing qualities are different. The unexposed Portriga keeps better over the years. I have boxes of Portriga and Brovira purchased together, kept together, probably late 1970's, and the Portriga is just fine (a little Liquid Orthazite in the developer to minimize age fog), but the Brovira does not seem to be generally salvagable.

Strangely enough I have 30 year old Brovira with no fog, my Portriga is mostly a bit newer but I suspect Ron is correct and if Portriga was compared with the same surface in Brovira they would be very similar other than the colour.
I don't worry too much about fog these days, I just use it up for lith prints where the fog often just doesn't show up or else as a lovely pink.
Mark