The rod float lightly on the surface of the paper. Several passes can be made over a sturdy paper like Bergger COT 320 with no buckling or abrasion (lifting up of the paper fibers). For a paper like Weston Diploma Parchment, the paper will start to buckle on the fourth pass when working quickly. I probably tend to make one or two too many passes with the rod on this paper. COT 320 is a easier experience.
Beth Moon does beautiful platinum and palladium work using Mike Ware's method. She makes prints as large as 16 inch by 20 inch. She surprised Mark Nelson and I when she said she rod coated even the large prints. I was always thinking I had to switch to a brush to coat the larger prints beyond say 11 inch by 14 inch.
Kim Weston taught me platinum/palladium printing with a rod and the ratio method, this was my first foray into alternative printing processes. Mark Nelson is uses a "magic brush" to brush coat his palladium prints. When I worked with him that first time he kep saying "magic brush" and I was getting worried about being alone with him in his house. He finally explained that this is the term used by platinum/palladium printers for the Richeson 9010 brush. Laying a similar amount of sensitizer as in rod coating - or perhaps a bit more - you pour the sensitizer from your shot glass used to mix it onto the paper and brush smoothly and rapidly to cover the area to print spreading the emulsion uniformly. It is with a brush that people go to the "artistic brush stroke" aesthetic of alternative printing. To show the hand coating of the paper. The "artistic" part takes some practice, as the result without forethought simply looks sloppy. There is one image that I routinely brush coat paper for to echo with the overbrushing strokes the lines in the image.
Take care to avoid getting emulsion into the metal part of the handle as it can contaminate your coating. Keep your brushes clean, rinse in distilled water, shake out firmly and hang to dry. Don't leave in a jar as this will eventually screw up your brush shape.
I've used Japanese Hake brushes with some success. They are gentle on the paper and the ones I have the bristles are sewn to the wooden handle so metal contamination is impossible.
There is not much artistry in the emulsion areas of a rod coated paper beyond the exposed image area. Many people cut a sheet of rubylith to mask the area against exposure when using a film negative, or create a digital negative with a dark border to print it white.
Judy Seigel and John Dugdale are fans of the black foam, wood handled brushes you can pick up at the Home Depot or other hardware stores. I struggle with this brush. With the Weston Diploma parchment, the foam brush raises the paper fibers. Perhaps I am too rough? John swears by them, they are cheap, and you won't get depressed when you dispose of them.
I played with coating large sheets of paper with a dense white foam roller I picked up at Home Depot. Inexpensive, washable. It is easy to doubly coat nicely with the foam roller. Lays an even coat down, seems to get the sensitizer into the paper mechanically without abrading the surface as I experienced with the black foam brush.
I've never soaked paper in sensitizer - thought I came close recently with cyanotype and Arches Platine (never could eliminate the mottling in the midtones with that paper).
I'm curious about commercial coating methods for cyanotype and platinum paper. Been scouting around for some historical descriptions - nothing has leapt out at me yet.