You rarely ever hear about Japan drier anymore. Im not sure why either…to me its almost required if your using a linseed or tung based finish.
I always add a few drops of Japan Drier when making up a new batch of oil. It really does help the finish dry out.
Back in the day when I used tru-oil….I thought it helped to thin it out a bit using gum turpentine or mineral spirits. I prefer the gum turpentine because I like the smell.