> Does anyone have some guidelines on when to use Japan drier in
> varnish?

Never!!

As far as I am concerned there is no need to speed up the drying of normal good varnish. Interlux formulate their varnish to allow drying within 24 hrs total. If you are below 10deg C then I would heat rather than add dryer.

Dust has been made out to be more of a problem than it realy is. In a good varnish job the sanding between coats is 220grit. Then the final coat is finished to 1200 grit then polished with #1 and # 3 automotive burnishing compound to a gloss finish. any dust particle smaller than 220g in the initial stages and 1200 in the final stages is gone with the sanding.

What I do about two hours before the final coat is spray my workshop with a mist of water and soak the floor. Solves the problem and I live in a desert where dust is a fact of life!!

Rob