For those curious about this, many papers contain oxidants or traces of oxidants added during the manufacturing process and that are used to bleach the pulp or rag. In addition, clays are added along with other metal salts to act as binders.
Baryta is about 10 g/meter sqare along with gelatin binder, and this offers a thick barrier to prevent transfer of chemistry as Ray says above.
This is why you will find that RC papers (raw stock) tend to keep better than Baryta, and in most cases Baryta would keep better than sized, and sized better than non-sized. The barrier effect is greatest with RC, and least with plain paper.
The whiteness also is improved, as is sharpness. A print on a baryta coat is sharper than one on sized paper which is sharper than on non-sized.
Now, I'm speaking strictly from the standpoint of traditional silver halide emulsion coated papers. The generalizations are too general for all types of alternate printing, I'm sure, but IDK for a fact. I just know how silver halide emulsions tend to behave under these conditions.
Oh, and it has been shown that addenda in baryta coated print materials diffuse slowly out of the emulsion layer into the paper support beneath the baryta. That is why keeping is worse, the less the barrier effect. Chemical exchange begins to become quite significant as path length decreases.
This would probably also be seen in processing these materials. There would be fluctuations introduced by changes in the thickness of the path length and the materials present. I know of no concrete studies on this though, just some vague theories and hypotheses. However, RC and FB do behave differently during processing. This much is known and that is where some of the vague hypotheses and theories have originated regarding unsized papers.
PE