December 5, 2025

French polish on a classical guitar — what you are actually paying for

You are standing in front of two guitars at a similar price. The first says: “French polish, shellac.” The second says: “polyurethane, high gloss.” The seller tells you the first one “sounds better” but cannot say why — and you have the feeling you are paying a few hundred extra for a phrase that happens to sound good in French.

It took me a long time to stop treating this as an argument about taste. French polish is not a better varnish. It is a different bargain: you give up durability, you get a thinner film. The rest of this piece is about exactly what you give up and exactly what you get.

What shellac is and where it comes from

Shellac is a resin secreted by the female lac insect, Kerria lacca, which lives in the forests of India and Thailand. The insects settle in their thousands on the branches of host trees and coat them with a layer of processed resin. The branches are cut, the material crushed, sieved and washed repeatedly, until nothing is left but shellac in the form of flakes soluble in alcohol.

It is one of the very few finishes of animal origin still used in the crafts. In India the insect is farmed on jujube, dhak and kusum; in Thailand on the rain tree and the pigeon pea. Everything after that is human work: dissolving the flakes in spirit and applying them with a pad, layer after layer, over many days.

And here is the first thing worth understanding: French polish is not a material, it is a technique. Shellac can be sprayed or brushed on — that gives you an ordinary shellac varnish. French polish means applying it with a pad of wadding wrapped in cloth, with a trace of oil as a lubricant, in circular motions, across hundreds of very thin passes. That is where the whole difference comes from.

What it means in numbers

This is where adjectives stop being useful. Film thickness can be measured.

Finish	Film thickness	Notes
French polish	0.03–0.08 mm	usually 4–8 times thinner than polyurethane
Nitrocellulose	approx. 0.1 mm	the standard on acoustic guitars
Polyurethane	0.20–0.25 mm	sprayed in 3–4 heavy coats

Eight hundredths of a millimetre is roughly the thickness of a human hair. Two tenths is already four hairs stacked on top of one another, glued to a soundboard that is supposed to move.

It is worth knowing that these figures come from luthiers describing their own practice, not from laboratory work with a control sample. Different craftsmen quote slightly different values, and I have seen the discrepancies between sources myself. The order of magnitude, though, is consistent everywhere: French polish sits in hundredths of a millimetre, polyurethane in tenths.

What you can hear

The soundboard of a classical guitar is around two and a half millimetres thick. The luthier sands it and thins it from underneath, fighting for tenths of a millimetre, because that determines how freely the whole thing will move. Then the finish arrives and adds mass and stiffness back on.

You can think of it as a blanket thrown over a drum. A thin scarf will change almost nothing. A heavy blanket will smother whatever that drum had to say.

Shellac sounds more open and sets some of the overtones free — those higher components that give a note its colour rather than just its pitch. Synthetic varnishes focus the sound more firmly on the fundamental. This is not a judgement, only a description of the difference: a more focused sound can be an advantage in a recording, and a more open one in a hall.

I had trouble with this for a good few years. I repeated after others that the difference in finish is always audible and immediately so — and I came to see that this is an oversimplification. An instrument with French polish came to me where I heard the difference from the first note, before I had even looked at the description. But others came where I heard nothing in particular, and I am not going to pretend otherwise. The finish is one of a dozen or more factors, not the only one.

Put briefly: French polish helps, but it will not rescue a badly built guitar.

What shellac cannot tolerate

Here begins the part sellers leave out most often — not out of bad faith, but because it spoils the mood at the till.

Alcohol. Shellac dissolves in spirit and remains soluble in it forever, including after it has fully cured. This is not a flaw in the material but its nature, and as it happens that nature also has a good side, which I will come to shortly. In practice it means this: hand sanitiser, perfume, aftershave and most household cleaning products will leave a permanent mark on French polish within seconds.

Water and sweat. A drop left standing for a quarter of an hour leaves a milky stain. Sweat is worse than water, because it carries salt and oil. Concert guitarists describe having to wipe the instrument down after a performance, before the residue starts to eat into the surface.

Heat. Shellac has the lowest softening point of any finish used on instruments. A hot car window, a radiator under the window, the warm padding of a stand — all of these can leave an impression.

Friction. A forearm resting on the edge of the body, a shirt button, a jacket zip. A film measured in hundredths of a millimetre has no reserve for wear.

The dull patch on the back

Instruments reach me with a dull patch on the back — exactly where the forearm rests, or where the guitar was in contact with a stand. The owners arrive convinced that this is a defect in the material, or that somebody cheated them on the quality of the finish.

Nobody cheated them. The French polish behaved exactly as French polish behaves. The problem is that when they bought the instrument, they were told about the advantages of a thin film, and were not told what that thin film means in contact with human skin for three hours a day.

That, in fact, is the only thing I hold against this whole story about shellac. Not the material — the fact that it is sold on its advantages alone.

The good news is that a dull patch is the mildest kind of damage that can happen. French polish can be refreshed locally, without stripping the whole finish — new shellac bonds with the old, because it dissolves it at the point of contact. With polyurethane, the same blemish means sanding back and refinishing the entire surface.

Is shellac really impractical

I have heard it many times, including from people who know their trade: French polish is beautiful but impractical, so it is better to choose something more durable. I understand where it comes from, and I thought the same for a long time. Today I consider it an oversimplification — and I would like to explain why, because this is not contrariness for its own sake.

The impracticality argument rests on a quiet assumption: that damage to the finish is the end of the matter. With synthetic varnishes it very nearly is. Repair means sanding, spraying and refinishing from scratch, usually the whole soundboard, in a workshop with a spray booth. The cost can be out of all proportion to the value of the instrument.

With French polish it is the other way round. Every new layer bonds with the one beneath it, so a repair means adding shellac where the damage is. There is no boundary between old and new. An instrument with French polish can be refreshed many times across decades, and that is a normal part of its life rather than a failure.

So yes: shellac is easier to damage. And considerably easier to repair. Calling it simply “impractical” loses half the picture.

That said, I am not going to talk anyone into it against the way they live. If you play rehearsals in clubs, carry the guitar in a car boot and have no patience for wiping the instrument down after every session — a synthetic varnish will serve you better, and there is nothing shameful in that.

Living with French polish day to day

None of this is difficult. It comes down to a few habits that become second nature within a month.

Wipe the instrument down after every session with a dry, soft microfibre cloth — particularly where the forearm has been resting. No cleaning products, no furniture polish, nothing with alcohol in it.

Put the guitar back in its case, not on a stand. The rubber and foam in stands can leave an impression in warm conditions, and with French polish a dozen or so hours of contact is enough.

If you sweat a lot, wear a light long-sleeved shirt or clip a protective guard to the edge of the body. Concert guitarists have used this solution for a long time and there is nothing embarrassing about it.

Do not keep the instrument next to a radiator or in a hot car. This advice applies to any guitar, but with French polish the consequences show up faster.

And most importantly: do not panic at the first dull patch. It does not mean you have done something wrong. It means you are playing.

When shellac, and when varnish

Your situation	The more sensible choice
You play at home, in the evenings, returning after years away	French polish — most to gain, least to risk
You are preparing a programme for an exam or recital	French polish, if the budget allows
You take the guitar to rehearsals and club gigs	synthetic varnish
A guitar for a child, or a first instrument	synthetic varnish, without hesitation
You sweat heavily and you know it	French polish with a protective guard, or varnish
You treat the instrument as a decades-long investment	French polish — it ages and repairs better

If you are looking at a luthier-built guitar and see French polish in the description, treat it as a signal that the builder did not economise on time. Applying a proper French polish is a dozen or more days of work spread across weeks, interrupted by drying. Nobody does this by accident, or as decoration for the label.

Common questions

Can you tell French polish by eye?
Usually yes. It has a deeper, warmer gloss than a synthetic varnish, and you can see faint streaks left by the pad if you look at it against the light at an angle. Polyurethane is more even and looks like glass — and it is precisely that perfect evenness that gives it away fastest.

How much does it cost to refresh French polish?
It depends on the scope. Touching up a dull patch locally is usually a minor job. Refreshing the whole body is considerably more expensive, but still cheaper than refinishing an instrument in polyurethane.

Does shellac yellow over time?
It darkens, and most people consider that an advantage. An instrument after twenty years has a colour that cannot be produced artificially.

Can I use an ordinary guitar cleaning product?
Check the ingredients. If there is alcohol in it in any form, no. A dry microfibre cloth is enough in nine cases out of ten.

Is the back finished in shellac as well?
Not always. Some luthiers use French polish only on the soundboard and finish the back and sides with something more durable. It is worth asking directly, because it changes the whole conversation about care.

Is it worth paying extra for French polish on a guitar at four thousand?
It seems to me that in that bracket it matters more whether the soundboard is solid and how the fan bracing is built. French polish on a well-built instrument makes a difference. On an average one it is mainly prettier.

Can I refresh French polish myself at home?
It can be learned, and many guitarists do it. Start on something you would not mind ruining — not on the instrument you care about.

Finally

French polish is not a choice between better and worse. It is a choice between an instrument that asks a few habits of you every day, and an instrument that will forgive you anything and, in return, say a little less.

A guitar with French polish does not look new after ten years of playing. It looks played. And that, to my mind, is the only sensible way for an instrument to grow old.