I had a beautiful Brazilian Rosewood guitar come into the shop with a bunch of hairline cracks in the back. This type of Rosewood is famous for developing cracks, especially if it is flat sawn and highly figured like the piece you see here. It is possible that these cracks went undiscovered in the building process and later began to show up in the way of cracks in the finish. Let me show you how I do this type of repair. I am going to use thin viscosity CA glue in a small pipette. Both of these items I got from LMI. I use the pipette to apply a small amount of CA to the crack. Since it is thin viscosity, it rolls right into the crack, filling the void in the finish, as well as stabilizing the hairline crack in the wood. Make sure to remove any dust or residue in the crack before applying the glue. Also, do not use accelerator after applying the glue, as it has a tendency to make the glue turn white. For any cracks in the wood that have not penetrated the finish, you need to apply pressure to them either from the outside or the inside of the guitar to separate the crack, allowing the CA glue to penetrate. Now that the cracks are repaired, the next step is to repair the finish. The finish on this guitar is catalyzed urethane. Therefore, it is necessary to spray the entire back instead of just where the crack were. If it were an evaporative finish like lacquer or shellac, I could get away with just touching up the cracked areas. I begin by using a small razor blade to scrape the CA glue level with the finish. I then scuff sand the entire back with some sand paper. Once this is done I wipe Naptha on the surface to see if there are any more cracks visible that might need to be repaired. If you notice any cracks that have white residue in them, you can get creative with a marker to hide them. I now mask off the entire guitar except for the back. This way, when spraying, I only get the finish where I want it. After some quality time spent in the spray booth and then leveling and buffing the finish, this is the end result.