A while ago I was asked about different types of lacquer and how luthiers are able to get their guitars to look as glossy as they do. Sometimes they look as if they’re dipped in glass! In this article we’ll take a close look at how luthiers prepare the guitar for finishing and the final processes of making the lacquer as shiny as possible but first, let’s take a closer look at the various types of lacquer, varnish and finishing products available. We’ve discussed the various types of lacquer in depth a while back, but it doesn’t hurt to recap some types of lacquer and finish.
My personal favorite is shellac. Shellac is a resin dissolved in alcohol. It can be sprayed on the project but more often than not, Shellac is the material of choice for French Polishing (a labor intensive, hand-rubbing technique to lay down layer after layer of lacquer). It’s completely natural and if properly sourced, organic and biological. It’s extremely easy to repair but also quite fragile but with the current craze of ‘relicing’ (especially naturally worn guitars), I doubt that fragility is much of an issue.
Another easy-to-apply product are the various types of oils. These products polymerize due to contact with air and leave a sturdy film on the wood. This can be a relative hard layer, hard enough to accept a high gloss. Other types of oil need to be reapplied annually.
Perhaps one of the most famous of lacquers, nitrocellulose has been a popular choice for guitars since its conception and introduction in the automotive industry up until, actually today, though I suppose the current popularity is more due to nostalgic reasons than any practical or tonal reason. Nitrocellulose has the advantage that it can be buffed to a high gloss with relative ease and ‘old’ layers of nitro will blend with freshly shot, new nitrocellulose. That’s also the disadvantage, though. You need to shoot many coats; sometimes up to 30 layers to get a high gloss! The toxic fumes require the user to use a ventilated, isolated spraying booth, as well as many safety precautions since nitro is very, very flammable!
Polyurethane is the to-go choice of the modern day. It is fast, easy, cheap and can be buffed to a high gloss as well. There are many who believe polyurethane has a plethora of disadvantages, such as being overly thick, non-porous, etc but most issues with poly can be negated if the luthier really knows what he’s doing!
There are other finishing products, too, like polyester and some acryllic paints, but they’re not nearly as widely used as the previous four I just mentioned.
Now we know the basic materials. Begs the question: how does the luthier use these products? Since the overwhelming majority of guitars is being finished in nitro(cellulose) or poly(urethane), I’ll be focussing my attention to the spraying method. Oil and shellac are rubbed on and have a different means of application. In the end, the polishing method as well as the preparation stages before the lacquers are even mixed, are essentially all the same.
When dealing with high gloss finishes the main question you have to ask yourself is: what makes a surface shiny? Simply put, a surface will be shiny if it’s dead flat. The flatter the shinier, essentially. This is because a superflat surface will deflect and reflect the rays of light instead of diffusing them all across the room. So, to make the lacquer super shiny, the substate on which the lacquer is applied needs to be as flat as possible. Remove all the lumps, crevices, cracks and whatnots, so the lacquer can be sprayed evenly. This means: sanding. Sanding till your arms fall off. You have to sand anyway, but the more time you spend sanding, the easier the lacquering becomes. When I do a high gloss finish I will sand the guitar up to grit 600. If I’m content with a satin gloss or a soft glow finish, I’ll go as far as 320.
Here, Michael Greenfield, one of the best builders of acoustic guitars, explains how he approaches sanding the guitar.
Wood has pores and these pores pose quite a bit of problems when finishing. The lacquer will drop in those pores and you’ll have to put on many, many coats to fill those pores if you want that ‘dipped in glass’ look! To save on lacquer as well as time (and money), pore fillers are used to fill the grain. They come in various forms. Sometimes they’re clear, sometimes they have a color (the deep cherry red of the mahogany backs on Gibsons is the result of a cherry red colored pore filler!). Sometimes they’re based on a wood slurry (wood dust mixed with solvents, glue or another adhesive and dyes), sometimes it’s a resin (epoxy or cyanoacrylate). Whatever the material, its goal is to form a barrier between the lacquer and wood, so the surface on which the lacquer is applied is as smooth as possible. If not that, the pore filler fills the pores as much as possible.
This is the easy part of the entire process. Shooting the lacquer. Poly requires much less coats and waiting time between the coats since poly cures (hardens) with UV lights whereas nitro and shellac require time to evaporate the solvents. All lacquers that are being shot with a spray gun require a good spray booth with proper ventilation and you don’t need to be a rocket scientist to figure out that these kinds of installations are amazingly expensive! What happens after the first few coats depends on the luthier. Some prefer to shoot all in one go, without sanding between the coats and others are adamant about sanding between layers. I prefer to shoot without sanding but that’s maybe because I shoot so little, so thinly that if I sand directly I go through the few coats I already shot with so much ease.
No matter how good you spray, the coat of lacquer will never be perfectly uniform. To combat that issue, you need to sand. There are specialized sand papers and micro meshes to do this job. They go up to grit 10000 if you look carefully! The standard procedure for most luthiers is to sand the lumps and bumps away with grit 600 dry and wet (I prefer micro mesh since micro mesh leaves less scratches than sandpaper!). After this initial sanding the lacquer is flat, finally! But… it’s full of scratches! So, now we take progressively finer mesh (or paper) to get rid of the scratches. Grit 1000, 1500 (or 1200), 2000, 2500 and then we’re finally getting there. Always making sure you don’t go through the film of lacquer. The technical term for that is bad.
Here, Dan Erlewine shows how he fills a small chip in the lacquer of a guitar. He uses progressively finer grit to ‘blend’ in the repair and this is the way it usually works when fine sanding a whole body.
Allright! We managed to get our surface flat and free of scratches! Now, we have to remove the final micro-scratches. They’re so tiny, you can hardly see them with the naked eye, but you do notice it because the lacquer is dull! So, whip out your polishing compounds and start polishing. Or buffing, depending on the terminology you prefer. There are several types of polishing compounds. You’ve got your paste, which is used in the automotive industry (often by amateurs or smaller pro shops). I prefer this paste cause I know it’s silicone free (silicones don’t play well with many types of lacquer). Also, this paste gives out a high gloss in a fairly short amount of time, even if you buff by hand. I don’t use a polishing wheel since I don’t have the space for it, but if I were I’d use jewelers rouge. This stuff is like a large brick of butter and you rub it on the buffing wheel.
The trick when using a buffing wheel is never to stop moving the body! If you stop, heat will build up and the heat will melt your lacquer and believe me, if that happens you’re in tears. After you pulled out all your hairs! To spend hours sanding, spraying and sanding again only to see all your hard work be rendered moot because you didn’t wiggle your hips while buffing is heartbreaking. So… move around.
Let’s see how Dan Erlewine is buffing his guitars. He explains exactly what I just described, but with a visual aid.
I prefer to omit the pore filler and use as little lacquer as possible. It’s just that we have to do it, but if it were up to me I’d make guitars with just a couple of coats of shellac, so the pores are open, the grain can be felt and the guitar will feel alive when you play it. But that’s just my personal preference.
What guitar brands do you think have the best looking finishes?