Repairing rosewood and ebony
copyright 2002 Aubrey Spurlock
Here are a couple of tricks that I have learned over the years. First of all, lets look at repairing small cracks. These will sometimes be found on fingerboards that have been in a hostile environment for a while, or between the bridge pin holes of bridges. These will crop up from time to time, even on very good guitars. Put a small drop of thin super-glue on the crack. This will go deep into the crack and find spaces in the wood below. If there is a gap between the bridge and the top, or the fingerboard and the neck, the thin glue will go there. Next put on a drop of medium super-glue and then immediately sand across the crack with 220 grit sandpaper. The wood dust will combine with the glue to form a filler that will seal the crack. Follow that by sanding with 320 and 400 grit sandpaper. If you use a circular motion, you can randomize your sand marks to make them less noticeable. The cracks will almost disappear.
For the string wear dips that sometimes appear on fingerboards of older guitars, there is another trick. During a refret or fret dress, sometimes the repairman will plane the fingerboard flat, removing these dips. However, on an old vintage guitar (especially those with thin fingerboards like old Fender's) you don't want to remove ANY wood if you can help it. I take a piece of similar wood and shave off various sized pieces with a sharp knife. Then I take a shaving that most closely matches the dip. I put a drop of super-glue in the dip (make sure it is clean and free of oils and grit). I place the shaving on the glue and clamp it firmly in place. I use a caul made of Plexiglas with the poly film still on. Super-glue will not stick to the poly film. When the shaving is pressed hard into the dip, it helps flatten it and squeeze out excess glue. After this has set, I use a file to level the shaving. Then I sand with 200 through 400 grit sandpaper. I wrap the sandpaper around a small block to insure that the repair is sanded flat.
To help color match either of the above repairs, I lightly sand the entire fingerboard or bridge with 220 - 320 grit sandpaper. Then I take a rag and rub in clear lacquer that has been thinned by 50 percent. This will darken the wood slightly and help protect it. I prefer this method over lemon-oil because it lasts longer and is more moisture resistant. Lightly rubbing with 0000 steel wool in a circular pattern will remove any marks left from the lacquer rub.
For other small cracks in rosewood and ebony, you can rub the appropriate powdered wood into the crack (collect some dust from sanding scrap wood). Follow that with thin super glue and then sand. You will get better results with ebony, but rosewood will sometimes look very good as well. The rosewood dust tends to get darker than the surrounding wood, but often looks like a natural streak or flaw in the wood. This method will even work to fill in small chips from refretting or other repair damage.