Guitar Finishes: French Polish, Lacquer and Polyurethane

Buying & Setup

The thin layer on the outside of a guitar affects how it sounds, how it ages, how it is repaired and what it is worth.

◆

What a finish actually does

Bare spruce or cedar would not survive long. It would soak up sweat and skin oils, stain, dry out unevenly and scratch at the first touch. A finish has four jobs:

• Protection: it keeps moisture, sweat and dirt out of the wood and slows the exchange of humidity between the wood and the air.
• Appearance: it brings out the grain and gives the instrument its look, from a deep, soft glow to a hard gloss.
• Surface: it makes the guitar pleasant to touch and easy to wipe clean.
• Sound: ideally nothing. The best finish protects the wood while interfering with its vibration as little as possible.

That last point is where finishes differ most. A soundboard is a membrane that moves. A thick, stiff coating adds mass and stiffness and damps that movement, while a thin, flexible one gets out of the way. Luthiers have argued about exactly how much difference this makes for centuries, and the effect is easier to describe than to measure. But nobody argues that a heavy finish helps.

French polish

French polish is the traditional finish for classical guitars and the one still preferred on most hand-built instruments. Despite the name, there is no polish in it. The finish is shellac, a natural resin dissolved in alcohol, applied by hand with a pad of cloth.

How it is applied

The luthier loads a pad with shellac solution and wipes it across the wood in small, continuous motions, with a tiny amount of oil to keep the pad from sticking. Each pass lays down an extremely thin film. The process is repeated through many sessions over days or weeks, with time to dry between them, until the surface builds up to a clear, deep, even layer. It takes skill, patience and a steady hand, which is why it is expensive. There are no shortcuts that give the same result.

How it sounds

French polish is among the thinnest finishes you can put on a guitar, and the shellac stays relatively soft. That is why it has such a strong reputation for tone, particularly on classical guitars, whose tops are built lightly and respond to small changes in mass. Many builders and players regard it as close to acoustically transparent. It is the standard against which other finishes are measured.

How it wears

The price of being thin and soft is vulnerability. Shellac scratches easily, and a fingernail or a belt buckle can mark it. It dissolves in alcohol, so spilled drinks and alcohol-based cleaners can damage it. Heat and moisture can leave pale marks, and a guitar left in a hot car can suffer badly. Skin acids from a forearm or hand slowly wear it away, which is why the area where the right forearm rests on a classical guitar usually goes dull before the rest of the instrument.

How it is repaired

Here shellac has a real advantage. Because new shellac dissolves and blends into old, a French polish can be touched up or renewed locally, and a skilled repairer can often make the repair almost invisible. A worn, dull area can be re-polished without stripping the whole guitar, so it can last for generations. Many fine instruments from the 19th and early 20th centuries still wear their original shellac, with a patina that collectors value.

◆

Nitrocellulose lacquer

Nitrocellulose lacquer arrived in the 20th century and became the default for much of the guitar industry, and a number of classical makers use it as well. It is sprayed rather than wiped, in a series of thin coats, with time to cure and then careful levelling and buffing to a gloss.

How it sounds

Nitrocellulose is applied thinly and stays fairly flexible, so it is usually considered a good partner for the wood. A thin nitro finish is generally regarded as acoustically friendly, although how much it matters depends on how many coats were applied and how thick the film finally is.

How it ages

Nitrocellulose is known for ageing visibly. It yellows slightly with time, which many people like, and it can develop fine cracks called checking, particularly when the guitar goes through sudden temperature changes. On a vintage instrument, checking is often treated as character. On a new guitar it is usually avoided. The finish also continues to shrink and harden for years as the solvents leave it, and it can be marked by some plastics and rubbers that react with it, which is why some stands and wall hangers warn against contact with lacquer.

How it is repaired

Nitrocellulose is relatively forgiving to repair. New lacquer bonds to old, so chips and scratches can be filled and blended in, and the repair can be made difficult to see. It is not as simple as shellac, but it is far easier than the harder, plastic-like finishes described below.

Polyurethane and polyester

Modern factories use polyurethane and polyester finishes because they are efficient. They are sprayed on, cured quickly, sometimes with heat or ultraviolet light, and then polished to a hard, glossy surface. A guitar can move through the finishing process in a fraction of the time that shellac needs.

How it sounds

These finishes tend to be applied more thickly, and the cured film is hard and stiff. Many makers and players feel that this restricts the movement of the soundboard compared with thinner finishes. On a solid, well-made guitar, the difference may be subtle, and plenty of good-sounding instruments wear polyurethane. On a lightly built classical top, it is more likely to matter.

How it wears

The advantage is toughness. Polyurethane resists scratches, alcohol, sweat and humidity better than shellac, does not yellow or check in the same way, and keeps its gloss for years with little care. For a guitar that will be carried around, played hard and not fussed over, that is a real benefit.

How it is repaired

The disadvantage is repairability. Cured polyurethane does not dissolve and blend into itself the way shellac and nitro do, so repairs tend to be visible, and a damaged area may need an entire panel refinished. That is one reason damaged polyurethane guitars are often valued lower than ones with a repairable finish.

Oil and wax finishes

Some makers, especially of acoustic and folk guitars, use oil or wax finishes, which soak into the wood rather than forming a film on top of it. They give a natural, slightly matte feel, and they have almost no mass, so their effect on the vibration of the wood is minimal. They protect less than a film finish, though. Moisture and dirt get in more easily, and the finish needs reapplying from time to time. Oil is most often used on necks, where the smooth, natural feel is appreciated, and some makers use it on the entire instrument.

◆

The three main finishes compared

	French polish	Nitrocellulose lacquer	Polyurethane / polyester
Applied	By hand, with a pad, over days or weeks	Sprayed in thin coats, then levelled and buffed	Sprayed, cured quickly, polished
Film thickness	Very thin	Thin	Usually thicker
Effect on sound	Closest to transparent	Light, flexible	Stiffer; more likely to dampen light tops
Durability	Soft; scratches, marks easily	Moderate; can check and wear	Hardest; resists scratches and moisture
Repair	Blends easily; can be renewed locally	Can be repaired and blended	Hard to repair invisibly
Ageing	Develops a soft patina	Yellows, may check	Stays almost unchanged
Cost to produce	Highest (labour)	Moderate	Lowest

Which finish suits which guitar

There is no best finish in the abstract, only the one that suits the guitar and the person who owns it.

• A hand-built concert classical: French polish is the traditional and usually the preferred choice, because the soundboard is light and responsive and the guitar will be looked after.
• A guitar that travels and gets played daily: a tougher finish earns its keep. Many players happily trade a little acoustic purity for a guitar they don't have to worry about.
• A steel-string acoustic: nitrocellulose is a long-standing favourite, and a thin polyurethane is a sensible modern choice. The soundboard is built more heavily and is less sensitive to the finish than a classical top.
• A vintage or collectable instrument: the original finish matters, and a refinish usually lowers the value. Check what has been done before buying.

◆

How to look after each finish

French polish

• Keep alcohol, solvents and alcohol-based cleaners well away from it.
• Never leave the guitar in a hot car or beside a heater, since heat and moisture mark shellac.
• Wipe it after playing with a clean, dry, soft cloth to remove sweat and skin oils before they can do damage.
• Avoid furniture polishes, which can contain silicones and solvents that cause trouble if the guitar later needs repair.
• If you play with a bare forearm, expect the contact area to dull in time. A repairer can renew it, and a clear protective sheet can slow the wear.

Nitrocellulose lacquer

• Avoid sudden temperature changes, which are the main cause of checking.
• Check that stands, wall hangers and case linings are lacquer-safe, since some foams and rubbers can react with nitro and leave marks.
• Clean with a soft, dry or very slightly damp cloth and a guitar-safe polish if needed.

Polyurethane

• Wipe with a soft cloth and, when needed, a guitar-safe cleaner.
• Do not assume it is indestructible. A hard knock can still chip it, and chips are difficult to repair neatly.

Whatever the finish, controlling humidity protects it. Wood that swells and shrinks with the seasons stresses the coating on top of it, which is one more reason to follow the advice in our humidity guide.

What to ask when you are buying

• What is the finish, and is it original? A reputable seller will know, and will tell you if the guitar has been refinished or repaired.
• Is the whole guitar finished the same way? Some builders use French polish on the soundboard and a harder finish on the back and sides.
• What does the wear look like? Look at the forearm contact area, the edges, the bridge area and the places where the guitar rests against a stand or a body.
• Is there any cracking, checking or lifting? Fine checking can be cosmetic, but lifting or cracks near seams and the bridge deserve a closer look.
• Has anything been touched up or overspray applied? Mismatched sheen, ridges or colour differences can show where a repair was made.

Price often follows the finish. A guitar finished by hand with shellac costs more than one sprayed in a fraction of the time, and part of what you are paying for is the labour and the skill. Whether that is worth it depends on how much you value the sound, the feel and the tradition.

The short version

French polish is the thinnest, the most transparent and the easiest to repair, but it is soft and demands care. Nitrocellulose lacquer is a thin, flexible middle ground that ages with character. Polyurethane is the toughest and the cheapest to produce, at some cost in repairability and, on lightly built guitars, possibly in sound. The right one depends on how you play, how you look after the guitar and what you want it to be. Learn to read the finish on any guitar you are considering and you will understand a good deal about how it was built and how it is likely to age.

A guide to guitar finishes: how French polish, nitrocellulose lacquer, polyurethane and oil finishes are applied, how they affect sound, wear and repair, and how to care for and buy a guitar with each.