My approach with 60-80 y/o Garand wood has been to saturate the wood with a mixture of odorless mineral spirits and isopropyl alcohol. All metal caps and liners, etc., should be removed beforehand. The solvent ratio is not critical as long as one or the other constitutes at least 1/3 of the mix, purer alcohols (90% vs 70%, 99% is usable but dries out hands unmercifully) can reduce grain welling from the included water. I do this in several passes, keeping the wood saturated by rewiping it with paper toweling saturated in the mix, and working over the surface with fine textured 3M Scotch Brite to remove old finish residue. Avoid rounding off any edges or decorative carving. Checkering can be scrubbed out with a moderately stiff brush (no metal).
Staining, as observed above on the shotgun forend, originating with metal contact, has a good chance of being at least partially due to iron oxidation staining. A mild acid, like lemon juice, can neutralize and also bleach out some of that; but you may have to live with some of it. I use unsweetened lemonade mix. Be very careful, acids/alkalines can ruin bluing. The acid itself may be neutralized with a mild solution of sodium bicarbonate. Finish it all up with another pass using the spirits/alcohol mix.
Eventually, give it a good chance to deep dry. Be certain it's bone dry.
Assuming an oil finish is the goal; use the chosen oil finish material oil, heavily diluted with the spirit/alcohol mix, to saturate the new cork-dry wood. Do it at least twice to drive that finish deep into the wood grain.
Again, give it a good chance to deep dry. Deep cracks get filed with a combination of the chosen finish material, very fine sandpaper, and elbow grease. Wet sand atop the cracks with this, using large circles to pick off surface wood evenly, building up a muddy slurry of very fine wood dust and the finishing material. Work the mud into the blemish, leaving it a tiny bit mounded.
This is a furniture refinisher's trick. It makes up a filler that's identical in solid and finish resin components to the overall wood and finish itself. It's indistinguishable from the natural wood. Allow it t dry/harden (this minimizes cracking), then cut it back down to the wood surface with the fine sandpaper.
This filling step should be repeated, with ample time for curing between passes, until very fine sandpaper shows only a sheen where the blemish once was.
This may take weeks, almost all of it spent waiting for things to dry/harden.
At this point apply the finish as you normally would. A thinner finish, rather than a thicker one, is my own personal goal. We use oil because it can be easily repaired.
Greg
