Old furniture may have a shellac finish, probably refinished at home. Knotty pine rooms also were treated normally with shellac. Keep moisture away from shellac surfaces. Water or a damp environment, as in humidity, makes shellac sticky. Test in an inconspicuous spot with denatured alcohol; shellac will dissolve quickly. Vacuum or dust regularly with a soft, dry cloth; do not use oiled or treated cloth.
You may protect the finish with a liquid furniture wax or cream polish that gives the desired gloss. If dirty, clean with either a cleaning polishing wax for furniture. Following the directions on the label for cleaning; or use a solution of equal parts of boiled linseed oil and mineral spirits. Moisten a soft cloth with cleaner and rub briskly, changing cloth when soiled. If surface is very dirty, process may have to be repeated. Use 3/0 or 4/0 steel wool to remove stubborn soil and smooth roughened places. If finish is in poor condition, use denatured alcohol to remove, and refinish with modern finish.