I don't wish to derail the thread by any means, but this talk of fumed silica has been very interesting and has started me wondering if it might be useful for something else; namely dye-imbibition.

Because fumed silica is used in micro-porous inkjet papers to accept pigment inks (which I realize are fundamentally different than dyes), I wonder if the same high surface area property that makes it suitable for this might act as a sponge/trap for dye solutions; thus reducing diffusion in non-mordanted receiving papers.

Just a thought... wanted to mention it. It's exciting to apply new materials to old processes.