Double Bass shellac retouching problem

[Matthew Tucker]

I'm trying to touch up some chips in the back of my ply bass.

here's an example of my task:

Its finished with a spirit varnish as far as I can tell. Softens with metho.

I've tried a few techniques to fill in the chips, and the best result so far is to melt some shellac in a bit of tin foil and then melt a bit of the resulting shellac stick into the chip with a hot knife, then sanding the lump back flush with the rest.

Other areas where the finish has been worn away (unnaturally, perhaps overzealous polishing by another owner) I'm trying to build the finish up by brushing on a layer of dissolved shellac. Sometimes this works, but other times the finish crinkles horribly where I paint on the shellac, I have to let it dry and sand it off again. I've tried rubbing on shellac on a french polishing rubber, but I get the same crinkliness.

Any idea what causes this and how i can solve my problem?

 

[arnoldschnitzer]

Shellac sticks won't work. Too thick and full of wax. Get some liquid shellac and colorants, mix a matching color and put on a few thin coats.

 

[Matthew Tucker]

yeah, i'm doing that but in some areas it goes all crinkly. Perhaps I'm putting it on too thick.

The melted shellac seems to work well in small sharp-edged nicks.

What do you do with the edges? feather them off with sandpaper, or try to level the area with shellac first then cut it back?

 

[Jazzdogg]

When I have to make those kinds of repairs I use the "french polishing" technique - applying extremely thin layers with a pad applicator - using either de-waxed shellac, qualisole, or Zinsser's so-called "French Polish."

If you haven't used this method before, it pays to practice on scrap first; I wouldn't try it for the first time on a valuable bass.

Here's a link to a tutorial:

http://www.homesteadfinishing.com/htdocs/padshellac2.htm

Good luck!