So far in my relatively short luthier career, I've sprayed nitrocellulose lacquer on about a dozen guitars. This has been the primary finish in guitar making for about the last 75 years, but at some of the big companies, they've shifted to UV cured polyurethane.
The learning curve for the best finish is steep and I've got my climbing shoes on! From mixing the finish to air temperature, humidity, dew point, spray guns, color and prep, it's a long road to a clean and clear result. The goal is as thin a finish as possible, while still protecting the instrument. Factory made guitars have very thick finishes generally. They look great, but that finish can kill your vibes! Ok, your sound.
At the moment, I'm in the throws of wet sanding the finish, which is done with very fine sand paper, not the Home Despot variety grit, but 800 to 1500, which you could polish your nails to a bright shine with!
Soaking the paper in water with a little soap!
It's a sloppy and dirty job, but someone has to do it. In this case, me.
The guitar parts, neck and body, are both wet sanded after soaking the paper in water (some use mineral spirits) before running succeedingly finer grits of paper until the nitro is actually flattened out on the guitar. This reduces the amount of finish and levels it to allow the clearest reflection when it is buffed, highlighting the wood grain below without hiding or obscuring it. Below is a five piece, maple and mahogany neck, made from individual pieces, carved and shaped, then sprayed. After waiting 7-10 days (or more in this case) it's ready for wet sanding and has been sanded to about 1000 grit in this photo.
After proceeding to 1500 grit and being careful not to sand through to the bare wood, the neck is checked visually for any shiny spots, which are further sanded, then buffed on a large wheel.
The whole process takes hours, with sanding by hand taking up the majority of time. It takes attention to detail and a fresh eye to spot the issues and produce great results.
The headstock or peg head on the left is untouched since spraying and the one on the right is closer to finished. You can see the little dimples (aren't they cute! 😂😫) In the finish on the left. Those are the enemy!
The one on the right is smooth and glossy after about an hour and a half on the whole neck. Necks are tricky due to the fact that most of the surfaces are curved and there are lots of edges where the finish doesn't like to stick.
So this is what fills many of my days and it's the reason that when you buy a hand made guitar, your not just buying the object, but your buying a little or not so little piece of the builders life. Now the price seems reasonable, doesn't it? 😉