Why Nitro Is Different
Nitrocellulose lacquer is a solvent-based finish derived from cellulose. It was the standard guitar finish from the 1950s through much of the 1970s, used on most of the instruments we now call vintage. It was gradually replaced by polyester and polyurethane because those finishes are faster to apply, more durable, and require less skilled labour to spray consistently. From a manufacturing standpoint, the logic is hard to argue with.
From a player's standpoint, the picture is more complicated. Poly finishes are essentially a hard plastic shell that sits on top of the wood. They are very resistant to solvents, temperature, and humidity fluctuation. Nitrocellulose, by contrast, remains slightly reactive to solvents even after decades of curing. It expands and contracts with temperature changes, breathes with the wood, and develops checking, tinting, and wear patterns over time. That reactivity is what makes it behave the way it does — and it is also what requires slightly more careful handling.
None of the following is difficult to manage. Players have been caring for nitro-finished guitars successfully for seventy years. The key is knowing what to avoid and why.
What Will Damage a Nitro Finish
Rubber and Foam
This is the most common source of unintentional damage. Rubber and many types of foam contain plasticisers that react with nitrocellulose over time, causing the finish to soften, stick, and eventually leave permanent marks. Guitar stands with rubber-padded yokes, foam-lined cases where the foam contacts the body, rubber-backed mats — all of these can damage a nitro finish if the guitar rests against them for extended periods. Use a hardshell case with fabric lining rather than foam, and choose guitar stands with fabric or leather yoke covers rather than rubber. If in doubt, drape a soft cotton cloth between the guitar and any foam or rubber surface.
Solvent-Based Cleaning Products
Because nitrocellulose is solvent-based, cleaning products containing solvents can partially dissolve the finish. This includes many all-purpose household cleaners, products containing alcohol (beyond very dilute concentrations), and any spray marked as a degreaser or solvent cleaner. Guitar polishes marketed for "all finishes" frequently contain silicones and solvents that are safe for poly but problematic for nitro. Use only products specifically marketed as nitro-safe, or simply use a slightly dampened microfibre cloth followed by a dry cloth.
Heat and Direct Sunlight
Nitro softens at lower temperatures than poly. Leaving a guitar in a hot car — common in summer, potentially reaching 60-70°C inside a closed vehicle — can cause the finish to soften, and in extreme cases, hardware to sink into the body surface. Prolonged direct sunlight is also more aggressive on nitro than on poly, accelerating yellowing and checking faster than the natural aging rate you might want. Store the guitar away from windows and heat sources. This is not fragility, it is simply sensible storage that applies to any fine wooden instrument.
Guitar Strap Rubber Backing
Many commercially available guitar straps have a rubber or synthetic gripper material on the back, intended to stop the strap sliding off your shoulder. This material can react with nitro finish over time, leaving a sticky mark along the shoulder where the strap rests. Use a leather strap, a vintage-style woven strap, or one explicitly marked as nitro-safe. It is a small thing, but preventable.
Routine Cleaning
After playing, wipe down the body and neck with a clean, dry microfibre cloth. This removes sweat, skin oils, and moisture before they have time to work into the finish. Sweat is mildly acidic and will, over time, dull a nitro finish and accelerate tarnishing on hardware if allowed to sit. This is the single most useful habit you can develop.
For deeper cleaning when the guitar has accumulated light grime, a microfibre cloth very lightly dampened with water works well. Wring out the cloth thoroughly — you want barely damp, not wet — and wipe the affected area, followed immediately by a dry cloth. Do not let water sit on the finish.
For the fretboard, assuming it is rosewood or ebony and therefore unfinished, a small amount of lemon oil applied with a cloth and wiped off clean every six months or so keeps the wood from drying out. Maple fretboards with a nitro coating should be treated like the body — dry cloth only, with the lightly-damp method for stubborn marks. Never apply oil to a finished maple board.
The best polish for a nitro guitar is a clean microfibre cloth used after every session. Everything else is occasional maintenance.
Humidity and Storage
Nitrocellulose is not unusually sensitive to humidity compared to poly, but the wood beneath it certainly is. Acoustic guitars are particularly susceptible. Ideal storage humidity is between 45% and 55% relative humidity. Below 35% for extended periods, the wood can dry out, leading to checking in the finish and potential shrinkage cracks. Above 65%, the wood can swell, and in severe cases the neck geometry can shift.
In the Netherlands this is rarely a problem in summer, when outdoor humidity is naturally moderate to high. In winter with central heating running, indoor humidity can drop significantly. A case humidifier is worthwhile if you are storing the guitar in a heated room for months at a time. The kind that sits in the soundhole of an acoustic, or inside the case between two cloths for electrics, is sufficient. You do not need an elaborate system.
Temperature fluctuations matter more than absolute temperature. A guitar that goes from a cold car (5°C) to a warm room (22°C) rapidly will experience thermal stress, and on a nitro finish this will contribute to checking over time. That checking is entirely natural and part of the appeal — but if you want to control the rate, warming the guitar gradually in its case before opening it helps.
What Normal Aging Looks Like
Owners of nitro-finished guitars sometimes contact us concerned about changes they have noticed in the finish. Most of the time, those changes are entirely normal and are precisely what makes the instrument more interesting over time.
Fine lacquer checking — the hairline crazes that develop in the finish — will continue to spread and deepen over the years. This is normal. New checking lines may appear suddenly after a temperature change, then stabilise. The finish will gradually yellow and amber, particularly in areas exposed to light. Any areas where your hand contacts the neck will develop a smooth, slightly worn quality as the lacquer thins.
None of this requires intervention. In fact, intervening — attempting to polish out checking, for example — is usually a bad idea. The checking is part of the character. Work with it rather than against it.
When Something Goes Wrong
If the finish has been damaged — a deep scratch through to bare wood, or a reaction mark from rubber contact — contact us before attempting any DIY repair. Nitro can be touched up successfully, but only with compatible materials applied correctly. Filling a scratch with a poly-based filler, for example, will be obvious under light and will not accept additional nitro coats in a natural way.
We offer finish repair and touch-up services for instruments we have built and for guitars from other makers. A genuine repair on a relic'd instrument should ideally be consistent with the aging level of the rest of the guitar — slightly aged to match rather than shiny new. We do this routinely for clients whose guitars have picked up fresh damage they want blended in. Read more about aging levels to understand what that process involves.