It will sound different, among other things. Guitar finishes continue to release solvents (called off-gassing) for decades, which is one of the reasons old guitars sound better than new ones. This is less of an issue on solid body instruments, but it is still and issue. It is also worth mentioning that any refinishing of an instrument (even if the finish is in very bad shape) will immediately cut it's vintage value in half (if it has any). An original finish is highly valued.
As for what we use, there are a lot of options for a professional quality finish, and there is a great deal of controversy about the subject right now. Since the 1930's, the most common finish is nitrocellulose lacquer, and nitro is traditional on all of the instruments which are currently in wide use. Nitro dries very hard, is quite durable, and is easily repaired (by a professional). The only repair problem is that it yellows as it ages, which means it is difficult to match colors. Nitro contains very volatile solvents, however, and so it is something of an environmental hazard, and can only be safely sprayed in a spray booth which is designed for such solvents. It is also necessary to use a respirator rated for organic vapors, as the solvents involved are highly toxic. None the less, there is little question to most people in the industry that nitro is the best sounding finish out there, and most of the companies who use other finishes (with a few exceptions) are using them because it is impossible for them to spray nitro due to environmental restrictions. Nitro is NOT a finish which can be safely sprayed by an amateur.
There are several alternatives to nitro on the market right now, though they all have problems to my mind. Luthier's Mercantile sells a water borne polyurethane, which is popular among the builders out in California due to their harsh EPA standards. A legal spray booth for nitro in CA is out of the range of most builders, so they either use the LMI waterborne, or they have their instruments finished by someone who has a legal booth (most sub out their finishes, because they want nitro). The main problems with the waterborne polys, to my mind, are the appearance, but they are also not very good sound wise. They just seem to damp the sound to me. Appearance wise, waterborne poly looks a little blue to me. They do not have the water clear look of nitro, plus they are always just a touch cloudy to my eye. I also do not like the way they age, as they stay mirror flat, and I like the way an older instrument looks, when the continued off-gassing causes the finish to sink into the grain of the wood. It is still glossy, but it has a little more depth to it. Waterbornes do not do this, and they also do not yellow, which I like the look of. They are, however, easy to apply, and can be applied with a brush or a spray gun, they are non toxic, non explosive, and they clean up with soap and water.
The third option, which is used by factories like Taylor, Larivee, and Tacoma, is UV cured polyester. Taylor innovated the use of these finishes due to the cost of spraying nitro in CA, and Bob has said he is extremely happy with the results, and would not go back to nitro even if he could. To me, they have the same problems as waterborne polys, namely they appear a little blue, they are just slightly cloudy to my eye, and they do not age. Additionally, they require a huge investment in equipment (the UV lights used to cure them are quite expensive, and if you look directly into the lamp without protection, they can blind you in seconds). This is, again, not a do it yourself project.
The oldest option is a French polish, but this has never been used on solid body instruments, and is incredibly hard to do well. I have only seen a handful of new french polished instruments that looked good, and there are very few people in the world left who have the skill to do a really good french polish.
As for process, if I was doing the job you are describing (which would cost north of $500, not including the air brushing, which I do not do), I would start by striping the finish. We use ZipStrip or CitruStrip for this. After the instrument is striped, we wash it down with naphtha, and then sand it, starting with 100 grit if we can, but frequently we would have to use 60 grit. We then proceed through the grits up through 150, and then pause to wet the wood. Next we sand again with 150, and then with 220. Then we are ready to start finishing, almost. You next need to tape off any part of the instrument which you do not want getting finished (the fingerboard, for instance). Then we spray a coat of sealer, followed by an application (or two if necessary) of pour filler. Next comes another coat of sealer, and then it is time for the first color coat. I use an opaque lacquer for color coats where you don't want to see the wood, but there are other options. In order to do a pink, I would have to make up a custom color for the instrument, which makes future touchup much more difficult. At this point, I would need to send the instrument out to the airbrush artist (if that is you, then you would pickup the instrument and do your thing). When you were done with the airbrushing, I would get the instrument back to do clear coats on. We generally do four or five coats, followed by a week of drying time, sanding with 320 grit fre-cut sand paper, another 3-4 coats, another week, another sanding, and two more coats. This is followed by about a month of drying time, and then we wet sand and polish. Then it is ready for reassembly.
I am sure some one is going to come along and tell me I am ridiculous for suggesting that this is what it takes to refinish an instrument, but anything less than this, and you will have a sloppy, unprofessional looking finish, which you are unlikely to be satisfied with. I have seen this many times, and many people are shocked when we tell them how much a good finish costs, but when they do it for less, they are unhappy.
Finish work on guitars is rarely worth the effort and expense involved. Add the extremely poor cost/benefit ratio to the fact that it damages the value and sound of your instrument, and I think you will find that it is not worth doing.
Light
"Cowards can never be moral."
M.K. Gandhi
