IN THE WOOD FINISH
The polished stone looking finish found on high end professionally finished stocks is the result of a process known as an “in the wood finish.”
Before you start: Make very sure that your hands are clean, anytime you handle a stock while it is being finished. Never handle raw wood with oil, grease or water on your hands. In the summer, be careful while leaning over a piece of raw wood and watch for beads of sweat. These things stain wood and the stain must be sanded out.
After you are done with the 220-grit paper on the last dry sanding of your stock, wet down the stock with a clean, moist piece of non-linting cloth. Using a hair dryer or heat gun, quickly and carefully dry the wet stock. Don't scorch the wood. This damp mop and dryer process "whiskers" the wood, leaving filaments of wood fiber sticking up from the surface. These fibers are important and are the material that will form the base of the wood filler that is so important in the method of the stock finish known as “in the wood” finishing. Set the stock aside to dry for 24 hours before applying any oil.
There are a number of good liquid stock finishes on the market. Each seems to produce an excellent and durable “in the wood” finish. I prefer Pro Custom Oil from Brownell's. Pro Custom Oil is a combination of Tung Oil and Polyurethane. I have used other stock finishes with this process, including True Oil, with excellent results.
IMPORTANT! Dilute the finish as it comes from the container. THE RATIO OF ONE PART FINISH TO TWO PARTS MINERAL SPIRITS is required. An empty pill bottle works well for the small amount of liquid needed.
The 1x2 solution is flooded over the stock surface with a small natural bristle brush until the wood will not accept anymore of the solution. The entire surface should be shiny wet. Be sure there are no dull patches, especially at end-grain areas. This first step ensures deep penetration of the liquid into the wood. Hang the stock and let it dry for two days. When dried, the “whiskered” wood fibers are hardened and standing on the surface. Now the “in the wood” finish process can begin.
Using 320 grit wet-or-dry paper backed by a squared rubber eraser (cut paper with scissors into 1 1/2" squares), the stock is wet sanded with the same 1 to 2 solution of the finish liquid. The wet sanding produces a paste filler of fine wood powder and finish oil combined into a slurry. The filler paste is the secret of this process. Fine details like stock fluting, shadow lines, rollovers, etc. are sanded utilizing backing devices such as dowels, pieces of rubber tubing with a dowel inserted, wedge shaped wood blocks, etc.
The very first (and each subsequent) sanding takes a time period of about 30 minutes. Wet sand the stock over every section with scrupulous attention to detail, using plenty of solution. Sand with the grain or in a circular motion, do not sand across the grain.
Now go back over the entire stock, using the two first fingers of your hand, to re-wet the entire surface with solution. Set the stock aside for five to eight minutes, allowing the surface to get a little tacky.
Next, rub the filler material into the pores of the wood. A brown paper towel (the same towel usually found in men's room rollers) is excellent for this. Crumple up 2 or 3 lengths about a foot long and, using a circular motion, rub the surface until the filler material has been rubbed into the pores or off of the stock. Do not polish the surface of the wood.
After the first application, the surface will appear dull. However, after two or three more applications, you should start to see dramatic results, as the wood pores fill in more and more.
After each application, the stock is hung to dry for 24 hours. The surface will not be sticky enough to attract airborne dust.
The third wet sanding with the 320 grit paper may fill the pores. However, each piece of wood has its own characteristics, so if after careful examination under a bright light, there are still unfilled pores, additional sanding with the 320 grit will be required. The sanding process should be continued until all pores are filled, each sanding coat separated by 24 hours' drying time. I have had some stocks require as many as 12 coats to fill properly.
Repeat the process with 400 grit wet and dry paper, allowing 24 hours' drying time. Once the 400 grit process results in a smooth surface, repeat the process using 600 grit paper. When you go to 600 grit paper use a soft cotton cloth instead of paper toweling and instead of rubbing in a circular motion, rub with the grain, until all trace of the filler mix is removed. The stock will now have a fine, hand rubbed sheen.
Subsequent rubs with rottenstone and oil may be required if you prefer a high gloss finish. If you go past the 600-grit finish, apply two coats of oil with your fingers, allow the oil to dry for a week then use rottenstone and paraffin oil on a medium weight felt pad (about 1-½ inches wide x 2 inches long). Smooth the finish with the rottenstone, being very careful not to cut through the finish to the wood. If you do go through to the wood, clean the surface with mineral spirits and start again with the 400 grit wet sanding.
Once the oil finish is done, apply three coats of Deluxing Compound. Deluxing Compound is a combination of fine paste waxes and 800 grit rubbing compound. It gives a durable wax coat to your stock and can be used to increase the sheen if desired.
This sounds like a lot of time and work, which it is. The finish is not meant to be a production finish. However, for custom pieces, the finish is spectacular.