I initially very lightly sand them when I first get them, then rub several very light coats of linseed oil on them over about a month. After that, I just wipe them with a cloth. Some of them are 40 years old, and still just take a wiping.
I buffed a pair of grips use linseed oil does a great job cleaning them up
Great finish to. Careful around the medallions. That may not be a good thing
for a collectable gun tho. ps
I degreased a set of S&W diamond grips , buffed them lightly with 4-0 steel wool then rubbed them with formbys tung oil and made an excellent looking set of walnut grips for my K32.