You are making all this unnecessarily complicated, unless that's what you want to do for the fun of it.
Any of the suggestions above, or consider Pilkington's spirit stains (Brownell's).
Forget the linseed and varnish home brew, and try one of the prepared polymerizing oil stock finishes which are really "light varnishes" (personally, I don't like Tru-oil, dries too fast), or use Minwax Antique oil or the similar product from Deft. They dry hard overnight (sandable) and cure completely in a week. They handle well in the process and give a true "oil" finish which is also tough and hard with only as much buildup as you care to allow.
There, the deep dark secret is out. That's a better magic witches brew than you could ever mix up yourself by the light of a full moon with human sacrifices and dinosaur blood. Put it up in a funky old bottle and act secretive about it and you will achieve master status before you know it.