If you apply shellac or lacquer to wood surfaces, you'll notice the finish will change color. Moisture causes the finish to turn milky. Shellac can be damaged by heat, humidity, and excessive cleaning. When shellac is scratched or marred, it dulls the wood and makes it appear dirty. A thorough cleaning restores the wood's original appearance, and applying a new coat of shellac covers the problem areas and hides the damage. You can fix this by spraying the finish with a solvent and letting it soak in. Let the finish harden overnight when the solvent is soaked in, then buff the repair with paste wax. The solvent will help loosen the finish from the wood. If you use shellac correctly, it's a beautiful finishing product. However, if you don't use shellac properly, you can create an unwanted appearance. The best way to maintain a clean and clear finish is to apply shellac in dry conditions. Never use shellac in humid conditions.