Squeeze all of the juice out of a medium-sized lemon into a bowl.
Pour 1 cup of olive oil into the bowl.
Dip a soft cloth into the bowl and wring it out.
Rub the cloth onto the scratched area. Repeat buffing the area until the scratch disappears. The acids in the lemon aid in fusing the scratch’s edges back together.
Dust the area with a clean soft cloth before filling the crack.
Select a filling material that has the same color as the tabletop. Common materials are walnut meat, shoe polish, crayons or a felt-tipped pen.
Rub the material onto the crack and allow it to dry, if needed. Walnut meat can be used directly out of a walnut. The meat acts as a filler and coloring agent in the crack.
Select the kind of finish on the tabletop. Original works prior to 1920 will have a shellac finish, while most others will be either a varnish or lacquer.
Clean the area with a soft cloth and paint thinner.
Dip steel wool into the appropriate solvent. Use denatured alcohol for shellac or lacquer thinner for all other types.
Rub the area until the flakes and other defects disappear.
Place a lump of paste wax into the center of a dry cotton cloth. Twist the cloth to trap the lump securely into the middle, and kneed the lump of paste wax. The heat from your hands will soften the wax. Rub the area with the lumped cloth and allow the wax to seep through. You do not have to rub in the direction of the grain. Continue rubbing until you see a glossy finish.
Heat a grapefruit or putty knife with an alcohol lamp, oil lamp, lighter or candle, and then heat the tip of the shellac stick. If you use a burn-in knife, then you will not need a heat source.
Apply the melted shellac stick to the crack and spread with the grapefruit knife. Continue this process until the crack is filled. If the shellac stick cools, then reheat it as needed.
Allow the compound to cool and shave off excess shellac with a razor blade.
Pour paraffin rubbing oil over the 400 grit waterproof abrasive paper and sand the area to create an even, smooth tabletop.