Nitrocellulose is used primarily on commercial musical instruments and is prized for its durability and glassy sheen. It is a vinyl-plastic formula that contains cellulose and is often tinted with brilliant colours. You can use it to repair scratches on guitars. It reactivates if another wet coat is applied to a dry coat, bonding them together. If a small amount of nitrocellulose is applied to a scratch, it works the same way to melt and blend the scratch into the fresh lacquer.
Dip a sharp, pointed stick into wet nitrocellulose.
Trace the scratch with the stick, using it like a pen to surgically apply just enough nitrocellulose to the scratch to cover it.
Apply more nitrocellulose to the crack if it doesn't disappear within 5-minutes. Wait 24 hours for the nitrocellulose to dry.
Fold a piece of denim into a small pad. Spray a short burst of furniture polish on the pad.
Polish over the crack vigorously in circular motions with authority, blending and polishing any remaining traces of residual nitrocellulose away until the guitar is gleaming.
Don't overdue it with the nitrocellulose. It only take a tiny amount to cover the scratch.
Don't breath fumes from nitrocellulose. It has toxic solvents that evaporate into the air. Wear breathing protection if you have more than one scratch.