I use Tung Oil (100% Pure or the Hardware store stuff) on Micarta and G10 handles after shaping them. Rub it in, let it sit for a while and then rub off any remainder. It will dry fully in a day or 2 and will help darken the handle. Many of the Micarta are not UV stable and will patina over time. OD Green turns brownish, brown/natural turns darker. Micarta is already stable as has been said, but after shaping a handle, it is lighter looking and the oil helps darken it up evenly. The oils in your hand will do the same thing naturally over time, but I find the Tung Oil (or Tru Oil, BLO, etc, oils that dry) helps keep the handle colors more even, patina evenly and not get stained as much down the road and make the handle more consistent looking than splotchy.
Patina examples in natural canvas, some vintage stuff. I cut scales from a 12x12 piece of micarta. I went across the piece and one scale was much darker all the way through than the other one was as seen in these pictures!
After a quick coat of Tung Oil:
Kinda cool, but not the look I was going for!! So I put the handle aside and over the next few months in my shop, the handle darkened up so the sides looked more even.
So I cut new scales from the middle of the piece:
The whole handle will eventually turn the darker maroonish color over time, but the lighter color is a nice contrast to the patina it will eventually get!
Just remember that Tung Oil/Tru Oil, BLO, etc will give a very slight amber/goldish color to the material as well and it will darken it slightly. I wash my handles down with Dawn soap and water, and then denatured alcohol and let fully dry before applying the oil coat to them to get any dust/oils/gunk off of them. I don't want to "seal" any stuff into the handle under the oil finish.
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