A little history: this type of coating was used heavily back in the day of blueprints. The patents show that the companies used it for increased contrast, sharpness, and paper stability. I have no way to guess how many millions of square feet this stuff was used, but some of the largest cyano companies employed this technique. In fact, we are doing some testing on a new paper that seems they might have caught wind and started applying this as well.
Thats interesting, is it possible to view these patents online regarding its use for blueprints and is there any historical evidence of its use for platinum/palladium printing?