How to I get my handles to look like this?

Gränsfors Tomahawk

How do I make my handles look like the Gränsfors Tomahawk linked above?

It says the handle is treated with a "Linseed oil stain" wich could be anything from a powder mixed with the oil to some rust or pine tar mixed in. Does anyone have a clue what they use? Or maybe I can mail them and get the recipe.