The methods used during wood finish repair projects will differ depending upon what type of finish was used. If the finish on the wood does not appear to be a lacquer or polyurethane, then it is probably shellac. Shellac is a type of wood finish made from a substance produced by bugs and was very popular before the early 20th century. One of the reasons shellac is still used in some applications today is that it is very easy to repair.
Step 1 – Determine That the Finish Is Shellac
To determine if the wood finish is indeed shellac, wet a rag with some denatured alcohol and dab it onto the wood in a place that is hidden from view (like the backside of a table leg). Because shellac is basically shellac flakes mixed into an alcohol base, alcohol will dissolve shellac. If after a few minutes the alcohol makes the finish sticky, it is likely that the finish is shellac.
Step 2 – Clean the Scratch
Make sure to clean the scratch thoroughly before attempting to repair. This will ensure that the new shellac bonds well with the old shellac and that no dirt or debris gets sealed into the finish.
Step 3 - For Light Scratches Apply a Second Coat
Because alcohol will dissolve shellac and shellac itself is alcohol based, simply applying another coat will fix light scratches. The new coat will dissolve a thin layer of the original shellac and blend the two together for a smooth polished surface.
Step 4 – For Medium Scratches Be Precise
For scratches that are too deep to simply re-coat, a little precision is required. Apply a thin bead of shellac into the scratch with a #1 or #2 sized artist’s brush. This will ensure that the shellac is dissolved and blended all the way down to the bottom of the scratch. Painting a second coat of shellac over a scratch too deep may only dissolve and blend the top layer of the finish. This would leave the scratch basically sealed below the finish where it would remain visible even though the top-most surface is perfectly smooth. The ideal consistency of shellac to use for this operation is a 1 pound cut (1 pound of shellac flakes mixed into 1 gallon of alcohol). This consistency is slightly runny and will flow easily into thin scratches.
Step 5 – For Deep Gouges Through the Finish and Into the Stain, Use Shellac Sticks
There are a few methods for deep scratches or gouges. The easiest method is to obtain a shellac stick. Available over the counter at most woodworking stores, a shellac stick resembles a crayon. Heat the stick until it is gooey and the rub it into the gouge. Use a hot putty knife to smooth it flat than sand the patched area to guarantee a smooth finish. If a shellac stick is not available, alcohol soluble pigments such as oil paints and fabric dyes can be mixed with the shellac. Try to blend the color so that it closely resembles the stain on the wood.