After sanding your wood piece with a final sand of P220 grit paper, remove the dust using either a vacuum or a tack cloth. Apply a coat of orange shellac and let it dry for 30-45 minutes. Now apply your first coat of varnish and let it dry for 12-24 hours.
If you apply the second coat the next day, there shouldn’t be any need to sand the first coat because the second will bond chemically to the first. If, however, more than a day has gone by since the first coat, the second coat will no longer chemically bond to the first, so you will need to scuff sand the first coat with P220-P320 grit sandpaper to give that second coat a physical bond.
Now it’s time to level the first two coats. After the second coat has dried for at least 24 hours, sand it with P220 grit sandpaper. Sand with the grain, using a rubber or cork sanding block on flat surfaces to keep the pressure uniform. Use your fingers only when you can find nothing else that will work as a sanding block—and switch to P320 grit so that you don’t cut through on edges or details!
As you level the surface, you should reveal a pattern of dull and shiny areas…the dull areas are the high spots being planed down by the abrasive and the shiny areas are the low spots that haven’t been touched. Don’t try to remove all the shiny areas completely, because you may accidently cut through on the edges.
After removing the sanding dust, apply a third coat of varnish. Let it dry for 12 to 24 hours. Now you’ll need to make a judgment call—do you have an unfilled pore pattern showing or do you feel that your first three coats were fairly thin? If so, now is the time to apply a fourth coat directly over the third. Let the fourth coat dry for 48 hours.
Sand this third or fourth coat with P400 grit SC Waterproof sandpaper, again using a sanding block. Lubricate the paper with water, adding a drop or two of dishwashing detergent to prevent clogging. Frequently wipe away the slurry to check your progress. If the varnish is making little balls on the sandpaper, that is an indication that your varnish needs to dry longer—even several days! Look for the same dull/gloss pattern as before, but aim for having fewer shiny areas and a flatter surface. Wipe down the piece with mineral spirits to remove any dried slurry.
For the final coat, thin your varnish with about 15% mineral spirits so that it flows on with virtually no brush marks, filling any hollows. Now let this final coat dry for at least 48 hours—but even longer is better. The harder the finish, the smoother the final result will be!
Now it’s time for your finish sanding. Begin with a light wet sanding in P1000 grit SC Waterproof sandpaper to remove the dust nibs and any small brush marks. If the sandpaper starts clogging, stop sanding and wait another day or two for additional drying of the varnish. Once you are in this final sanding stage, regularly check your progress until 80-90% of the surface is dull. Go light on the edges and small details.
Next, wipe down the piece with a damp sponge and clean water. Repeat the sanding process with sandpaper in P2000 & P3000, being careful to always clean the surface entirely before moving onto the next grit. You should only have a light sprinkling of low, shiny freckles left behind on the flat surfaces. You can continue this process all the way up to a P 5000 grit sandpaper finish if you would like! Finish by rubbing out to the desired sheen with a wax.
You can find all of the sandpaper mentioned in this blog post on Abrasive Resource's Online Store.