Nitrocellulose lacquers seem to be a favorite of those that do a lot of marquetry. It is not the perfect finish because there are trade-offs. First, it has a tendency to yellow over time (acrylic lacquer would be a better choice). The equipment and space needed can increase your overhead. Then you can have problems with blushing, orange peel and fisheye. Often several coats are needed to get an acceptable finish (too many coats can cause problems like crazing). Thinning the lacquer can be an exacting science and did I mention that the fumes are toxic. Having worked in cabinet shops that make furniture I can tell you that lacquer is not only the preferred choice, but the only choice. Time is money and the less you use of both the more competitive you are. This does not, however, translate into quality. Ask a violinmaker what finish he uses and I bet it won’t be lacquer.
Shellac is similar to lacquer in the way it cures. It has stood the test of time and is used still today. It can be applied in a variety of ways to just about anything including food. Shellac is an organic, naturally occurring substance that will not react to other finishes. Applying it underneath or on top of other finishes provides good adhesion. The drawback is that its amber color (even bleached shellac) will darken when too many coats are applied. I have found that 3 coats are enough to protect any marquetry. Anymore than that it will shrink and tint light-colored woods like maple and holly. It also is not waterproof, but can be easily repaired. Recently, I did a piece of marquetry in one weekend including the finish. It had a medium amount of detail with a protective finish. The keyword here is to protect not idolize a piece of furniture.
There are other finishes like varnish, epoxy and rubbing oil that can be used. The time it takes for them to cure can take anywhere from a few days to months. Some can be repaired while others cannot. It is the function of the finish to not only protect the marquetry, but to enhance the texture and grain of the wood. Putting on layers and layers of finish does not bring out the true qualities of marquetry. If the design is well executed, this should be its focal point. It is said that Jean-Charles Spindler uses nothing more than wax to finish his pictorial marquetry. We should take a lesson from him.
