In some ways, this is the most difficult part of making a harp. Up until this point, whenever I want to putter around in the garage there would always be something for me to do on the harp. Now I have to wait between coats of polyurethane.
The can of polyurethane says to wait four hours between coats, but that is NEVER enough. Not if you want a mirror smooth surface. My woodworking consultant, Heidi, always waits several days between coats. I've compromised for my own method. I wait 24 hours after the first coat, 72 hours after the second coat, and then three weeks after the third coat before tuning up.
Before each coat I sand the whole harp down with 220 grit sandpaper, then remove all dust and oil using a rag dampened with mineral spirits. Oil from my skin can affect the polyurethane, so it is important that once I start this process I never touch the harp without gloves on.
There are probably as many methods of applying polyurethane as there are woodworkers. This is the one I use: using a one-inch fine bristled paint brush and working one small area at a time, brush the polyurethane on against the grain, then smooth it in with the grain. That way I go over every area twice, ensure a thin coat, and catch any drips that might try to happen.
And there you see the result. Just look at that baby shine!
Once the polyurethane is dry, I can paint a design on the soundboard. First I do a line drawing with my drafting pen and waterproof ink. Then I paint using the same wood stain that I used on the body of the harp. Wood stain is a difficult medium to work with. If you try to paint over an already painted area, the fresh wood stain dissolves the older wood stain and forces all the pigment to the edges of the wet area. So you paint the dark areas first, then lightly brush in the lighter areas around them, trying hard not to bleed the new paint into the old. Of course I do use this interesting property of wood stain to good effect. I can create light colored veins in leaves by painting on a partially dry dark leaf.
For more info on how to build a harp, visit my How to Build a Harp page.