Revarnishing an old violin is a tricky business. The general rule of thumb, suggested by professional violin restorers, is to not revarnish a valuable old violin because revarnishing affects the sound quality and decreases the value of the instrument. On the other hand, if the old violin is not a high-quality instrument, removing the old finish and applying a new coat of varnish can significantly improve the appearance of the instrument. The process takes time and patience.
Remove the strings from the violin. Set up a work area in a lighted and dust-free environment.
Clean the violin with mineral spirits. Gently wipe the violin with soft cloth and mineral spirits to remove oil and grease buildup on the wood.
Sand off the old varnish with a fine-grit sanding block. Apply a light amount of pressure and sand in the direction of the grain. Wipe the violin with a soft cloth to remove the sanding dust after sanding off the old varnish.
Apply a ground coat to the violin with a small bristle brush. Ground coat is available at violin stores and online. Violin makers and restorers use the ground coat to add color and enhance the wood. Ground coat also strengthens the wood and prevents the varnish from penetrating the wood.
Purchase violin varnish and brushes at an online violin restoration site or at a violin or acoustic instrument store. Professional violin restorers recommend against making your own varnish.
Apply the varnish to the violin with a small bristled brush. Practice varnishing a piece of wood several times if you are inexperienced with varnishing techniques. Varnish has a much thinner consistency than paint. It is important to go slowly to prevent the varnish from running or building up heavy spots. Once you feel comfortable with your technique, apply a light coat of varnish to the violin. Hold the violin by the neck and apply the varnish, working with the grain of the wood. Allow the varnish to completely dry.
Sand the finish lightly with 180-grit sandpaper. Continue sanding until the finish feels smooth to the touch. Wipe the violin with a soft cloth to remove the dust and then apply a second coat of varnish.