Luthiery Laboratories

Minor dings in bare wood can often be popped out by applying a bit of boiling water, which will swell the grain. If water doesn't work, try heated acetone. Place a small container of acetone in a large container of hot water to heat it, away from any ignition source. Steam will also work - to fix up large areas, use an iron on low over a damp towel. I have even gotten the hot water trick to work through a finish, but there is no telling what the result may be, and I don't recommend trying it.

It may take several applications to get the full benefit. The softer the wood, the better this trick works. Poplar, alder, and pine can often be repaired completely. Maple responds less well. Always do this trick before sanding, if you do it after, you'll actually end up with a raised bump where the ding was!