I wonder... Am I to read this as meaning the flat blotter style (1850) is older than the rocker blotter style (1880-1950)? Will search some more...
Before the rocker blotter, you would purchase a blotting PAGE -- a full sheet of blotting paper. The purpose of blotting paper is to blot the excess ink from a handwritten letter. As such, you would use the blotting paper two ways -- you would lay a full sheet over a completed page of a letter or other document, and blot the entire page in one swoop; or you would lay a piece under your hand or sleeve, to prevent ink from staining as you write or move from paper to inkwell.
The rocker blotter comes into being in the industrial revolution, with the rise of the typewriter -- essentially, when the only thing you need to blot is the signature. Its size made it handy for ladies to write little notes -- invitations, short messages, dinner menus, etc.
Blotting paper was larger than the standard paper of the era. The most famous literary use of blotting paper was by Jane Austen, who -- while working on her novels in the drawing room -- would hide the pages of her works in progress under a sheet of blotting paper, when a visitor came to call.
