Lacquer is the most commonly used finishing product for both wood furniture and guitars. It is very durable and adds a nice sheen to the object it's applied to. Modern lacquer consists of a resin called nitrocellulose and a few other ingredients. The chemical make-up of the lacquer allows once coat to slightly dissolve as a second coat is applied. This allows the coats to blend together. Furniture and guitars are typically coated three to five times, but the end result is one strong coat rather than three to five separate coats. Despite its durability, lacquer is still subject to nicks, scratches and gouges.
Wipe the guitar with a clean cotton cloth. The goal is remove loose dirt and dust from the guitar so that the extent of the lacquer cracks is more visible.
Dampen a piece of 1,000-grit sandpaper with water and dish-washing detergent. Lightly sand the damaged area with the sandpaper. Lacquer is applied in several coats. The goal is to lightly sand the top coat of the lacquer to remove the surface scratches.
Apply a buffing compound to the damaged area. Buffing compound is available at home supply and auto parts stores. Follow the directions on the container. Apply the compound with a clean cotton cloth and allow it to dry to a paste-like consistency. Buff the guitar with a clean cotton cloth until the shiny surface of the guitar reappears.
Wipe the furniture with a clean cotton cloth to remove surface dust and dirt. Clean the damaged area with a wax precleaner and a cotton cloth. Apply the polishing paste to the area with a cotton cloth. Allow it to dry and then buff the area with a cotton cloth. The wax precleaner and the polishing paste remove small surface scratches, and this may be all you need to restore the piece of furniture. To repair larger scratches, nicks and gouges, proceed to the next steps.
Repair minor scratches, nicks and gouges with a furniture touch-up marker or putty stick. Furniture touch-up markers are available at office supply stores. They are inexpensive (around £3 for a package of three, as of 2011), available in several colours, and easy to use. Select a colour that matches the furniture and colour the gouge, nick or crack until it is filled. Furniture repair putty sticks work well on nicks, gouges and cracks that are a little more severe. They are also available at office supply stores in a wide range of colours.
Repair deeper cracks and gouges with a burn-in stick if the damaged area cannot be repaired with a marker or putty stick. Protect the surrounding area around the damaged spot with masking tape. Use an opaque colour for a shallow gouge and a transparent burn-in stick for deeper gouges or nicks. Heat up a knife with a flame. Hold the burn-in stick to the knife until it starts flowing on to the knife. Fill the gouge or dent with the knife, slightly overfilling the hole. Allow the repaired area to harden. Lightly wet sand it with 400-grit sandpaper. The repaired area has to be stained so that it blends in with the surrounding area.