Lacquered furniture may appear fragile and easily marred, but that is not always the case. Modern lacquer processes are not as fragile as older lacquering techniques. Determining whether the lacquer is fragile and needs further help is the first step to knowing whether it should receive an overcoat. Polyurethane may not be the best choice for protecting an ordinary lacquer.
Some lacquer finishes can be vulnerable to scratches and water damage. Test the furniture to determine what type of lacquer finish was used—ordinary lacquer or catalyzed lacquer. Catalyzed lacquer is very hard and durable. Find an inconspicuous spot on the piece and rub it with a cotton tip swab dipped in lacquer thinner. If the thinner causes the lacquer to become sticky, then the finish is ordinary lacquer. Catalyzed lacquer finishes will not respond to the thinner and it really is not necessary to protect them.
Covering the Finish
There are several things to keep in mind before moving forward. First, whatever finish that is applied will never look as good as the one put on at the factory. Second, polyurethane is not the best choice for painting over lacquer finishes. Polyurethane will not bond or grip well with the lacquer and will peel off over time with general use. Instead, use an alkyd varnish. Alkyd varnishes are a polyester resin that will adhere better and repair more easily. Their appearance looks more natural and does not tend toward yellowing. Make sure the alkyd varnish has a finish that matches the lacquer finish—a gloss finish is a safe bet. Lacquer should not be placed over a varnish because it contains a stronger solvent than a varnish and will eventually eat away the finish underneath.
Clean away all wax, oil or polishes that may be on the surface of the lacquer by wiping it down with naphtha. Use a 400-grit sandpaper to rough up the surface of the lacquer. Roughing it up this way will allow the varnish to hold better. Wipe down the roughed-up surface with a damp rag to remove the dust from sanding—a clean surface is important when applying varnish. Apply the varnish according to the manufacturer's directions. Generally, varnish can be applied using a foam applicator or brush. Allow each coat to completely dry before applying the next.