BLO would be my guess, check with Hugh Clark, he can tell you what it does to the shade/color/tint versus tung oil which i think he uses a lot and I believe Tung oil is darker. I love the light color they are now. BLO when applied will soak partially into the wood but you dont want to leave excess in the checkering as it will harden into crystals. When I apply it on the grips, I usually let them set for about 5 minutes then blot out the excess. Hugh's email is
hhclark@wildblue.net