Like Kerik said, it depends on the paper. I use it for some papers and not for others 1 drop for 8x10 for palladium prints. BUT - also use 1 drop of Everclear (190 prf - which is not available everywhere) and must say for smoothing out my coating it made a big difference. I use both with Fabriano Artistico Extra White (that is pre treated ahead of time with Oxalic acid).
When using tween be sure to notice if it starts to grow anything - which it will sooner or later. Think the last bottle lasted me about 4-5 years before it became some strange blob. As with most of what we do with alt process find what works for you - what works for some does not seem to work for others (and darn if I know how or why?)