Ask ten experienced Japanese sword collectors which oil they use and you will get at least four different answers. Traditional choji oil. Pure mineral oil. Synthetic sword oil. Camellia oil. Some will defend their choice passionately; others will say it scarcely matters. This diversity of opinion reflects a genuine uncertainty in the specialist community — and a market in which products sold as "choji oil" often contain no cloves whatsoever. This article cuts through the confusion: what each category of sword oil actually is, what the real differences are in practice, what to avoid, and what Tozando recommends based on more than thirty years of handling genuine nihonto.
First — What "Choji Oil" Actually Is (and Isn't)
The term choji abura (丁子油) literally means "clove oil" — oil derived from the clove plant (Syzygium aromaticum). Historically, the term referred to an oil preparation used for sword maintenance that incorporated clove-derived compounds, valued for the antioxidant properties of eugenol (the primary active compound in cloves) and, practically, for the distinctive pleasant fragrance that made a blade's maintenance a sensory as well as a technical procedure.
Here is the reality of the current market: the majority of products sold today under the name "choji oil" or "sword oil" contain no cloves at all. They are mineral oils — petroleum-derived rust-prevention oils — that have been given the choji name either by tradition, by marketing convention, or simply because the name is what customers expect to see. Some add a small amount of clove scent as a nod to the tradition; many do not even do that.
This is not a scandal or a fraud — mineral oil is a perfectly legitimate choice for sword maintenance, as we will discuss below. But it means that the name on the bottle is not a reliable guide to what is inside it. When evaluating any sword oil product, the relevant question is not "does it say choji?" but "what is the actual base oil?"
The Main Oil Types — What Each One Is
The historically authentic preparation: camellia oil (椿油, tsubaki abura) — a non-drying vegetable oil with good rust-prevention properties — blended with clove essential oil (丁子精油). Research into the history of choji oil suggests the likely formulation was approximately 9 parts camellia oil to 1 part clove essential oil, though the precise proportions were never standardised and varied between makers.
The clove component contributed eugenol — a natural antioxidant that helps prevent the camellia oil itself from oxidising, extending the oil's effective life on the blade. The fragrance was a secondary but appreciated benefit. Products using this authentic formulation are rare today and typically more expensive than mineral alternatives — some specialist makers in Japan still produce them.
- Historically authentic — the approach the tradition developed
- Eugenol's antioxidant properties may extend effective oil life
- Pleasant fragrance — part of the traditional maintenance experience
- Food-safe components — no concerns about skin contact
- Plant oils oxidise over time — requires more frequent replacement
- Higher viscosity — can be harder to apply and remove evenly
- Genuine products are scarce and more expensive
- Most products marketed as "choji oil" are not this
Pure camellia oil — without clove addition — has a long history as a rust-prevention oil for blades in Japan. It is a non-drying oil that forms a stable protective film and does not damage blade surfaces. It is available from ordinary pharmacies and beauty suppliers, making it the most accessible traditional option.
The main practical concern with camellia oil is its tendency to oxidise over time. An oxidised plant oil on a blade can become more acidic, potentially contributing to surface corrosion rather than preventing it. This does not mean camellia oil is unsafe — used with regular replacement (every 2–3 months rather than 3–6), it performs adequately. But it does mean the re-oiling interval matters more with plant oils than with mineral alternatives.
- Widely available from ordinary suppliers
- Completely food-safe — no concerns about skin contact
- Traditional material with centuries of use history
- Oxidises over time — requires shorter re-oiling intervals
- Higher viscosity than mineral oils — slightly harder to apply thinly
- Aged camellia oil may contribute to rather than prevent corrosion
Refined mineral oil — petroleum-derived rust-prevention oil — is what most sword oil products on the market actually contain, regardless of what the label says. This is not a recent development: the shift from plant-based to mineral-based sword oils occurred gradually through the 20th century as the mineral oils' superior rust-prevention characteristics became evident.
Mineral oils have two significant practical advantages over plant-based alternatives: they are more resistant to oxidation (they do not go "off" in the way plant oils can), and they are lower in viscosity, making them easier to apply and remove in the thin, even coat that is the most important factor in good blade maintenance. Many specialist Japanese sword dealers, polishers, and even the Bizen Osafune Sword Museum use high-quality mineral or synthetic oils precisely because of these practical advantages.
The main concern with early mineral sword oils was the presence of sulphur compounds in lower-quality formulations, which could cause black discolouration on steel. This problem has been largely eliminated from reputable sword-specific mineral oil products — the low-quality early products that caused issues have been displaced by better-formulated alternatives. Using a sword-specific mineral oil from a reputable supplier (not generic machine oil or WD-40) avoids this risk entirely.
- Does not oxidise — longer effective life on the blade
- Lower viscosity — easier to apply in a thin, even coat
- Easier to remove completely when re-oiling
- Used by many specialist dealers, polishers and museums
- Generally more affordable than plant-based alternatives
- Lower-quality formulations may contain sulphur — use sword-specific products only
- No traditional fragrance
- Petroleum-derived — some collectors prefer plant-based materials
The most technically advanced option for sword maintenance — and the choice of some of the most conservative custodians of significant blades. High-quality synthetic oils and silicone-based oils offer excellent oxidation resistance, consistent viscosity across a wide temperature range, and chemically neutral interaction with steel surfaces.
Notably, the Bizen Osafune Sword Museum uses silicone oil for the blades in its own collection — a choice that reflects the museum's assessment of long-term performance for blades that need to remain in stable condition across decades of storage and display. The NBTHK itself has moved toward mineral and synthetic oils in its maintenance recommendations in recent years.
For the international collector maintaining blades in varied climatic conditions, the temperature stability of synthetic oils is a practical advantage: the oil's behaviour does not change significantly between a cold winter and a humid summer, whereas plant-based oils can become significantly thicker in cold conditions.
- Excellent oxidation resistance — the most stable option
- Consistent viscosity across temperature ranges
- Chemically neutral — no sulphur or acidic compounds
- Choice of museum-grade conservation for significant blades
- Not traditional — no historical precedent in sword maintenance
- Some formulations may be difficult to remove completely with standard nuguigami
- Less widely available from specialist sword suppliers
WD-40 and similar penetrating sprays — WD-40 is a water-displacing spray designed for loosening corroded metal parts, not for long-term rust prevention. It evaporates rapidly, leaving minimal protective film, and is not appropriate for sword maintenance. Some collectors use it in emergencies to displace moisture; it should always be followed immediately by proper sword oil if used at all.
Generic machine oil or cooking oil — Cooking oils (olive oil, vegetable oil, sesame oil) oxidise rapidly and can become acidic, actively promoting corrosion on a blade surface. Generic machine oils may contain sulphur compounds or other additives incompatible with polished steel. Neither is appropriate regardless of what is available.
Non-specialist mineral oils from hardware stores — The concern is sulphur content and other additives designed for mechanical applications. Use only sword-specific mineral oils from reputable Japanese sword suppliers.
than how you apply it and how often you replace it.
A thin coat of any good sword oil,
replaced every three months,
will serve your blade better than
the finest oil applied incorrectly."
Quick Reference — Oil Types at a Glance
| Oil type | Oxidation resistance | Ease of application | Best for | Tozando verdict |
|---|---|---|---|---|
| Traditional choji (genuine) | Moderate — replace every 2–3 months | Slightly thicker | Traditionalists; historical authenticity | Excellent if genuine; rare and expensive |
| Camellia oil alone | Lower — replace every 2 months | Slightly thicker | Traditional preference; accessible | Acceptable; monitor re-oiling intervals carefully |
| Mineral sword oil | Good — replace every 3–6 months | Easy — lower viscosity | Most collectors; practical standard | Recommended for most collectors; use sword-specific products only |
| Synthetic / silicone oil | Excellent — most stable option | Easy — consistent viscosity | Significant antiques; museum storage | Excellent for long-term storage of high-value blades |
| WD-40 / cooking oil / machine oil | Poor or harmful | — | Nothing | Do not use on nihonto |
Tozando's Recommendation — What We Use and Why
After more than thirty years of handling genuine nihonto — including antiques ranging from Kamakura-period masterworks to Edo-period pieces, and newly forged blades by living masters — Tozando's position on sword oil is practical rather than dogmatic.
For the majority of collectors, a high-quality sword-specific mineral oil is the most practical choice. It does not oxidise, it applies and removes easily, it is widely available, and it is what the majority of serious Japanese sword specialists — dealers, polishers, and museum conservators — actually use in practice. The traditional choji name has sentimental and historical resonance; the mineral oil in most "choji oil" bottles performs well.
For collectors storing significant antiques — particularly Kamakura or early Muromachi blades in exceptional condition — a high-quality synthetic oil offers the most stable long-term protection. The Bizen Osafune Sword Museum's use of silicone oil for its own collection reflects the considered judgement of specialists whose priority is preservation across decades, not adherence to historical convention.
Whatever oil you choose, the following principles matter more than the specific product:
Apply thinly. Excess oil pools in the habaki, runs into the saya, and attracts dust. A barely visible sheen across the blade is the correct amount. If you can see the oil clearly, you have used too much.
Replace regularly. All oils — plant-based and mineral alike — degrade over time. Every three months for stored blades, more frequently for blades in humid environments or regular handling. An oil that has been on the blade for a year is doing nothing useful and may be contributing to surface oxidation.
Remove the old oil completely before applying new. Layering new oil over old is a common mistake that produces an accumulating film rather than a protective coating. A thorough wipe with clean nuguigami or tissue paper should precede each application.
the same quality used by Tozando's specialists
Tozando's complete maintenance kit includes high-quality sword oil, authentic uchiko, nuguigami, and brass mekugi-nuki — the same tools used by our Kyoto specialists. Available individually or as a complete kit, shipped worldwide.
In Closing — The Name Is Tradition; the Contents Are What Matter
"Choji oil" has been the name for Japanese sword maintenance oil for centuries. That name will persist long after the last product containing actual cloves has left the market. It is a name that carries the weight of tradition, the memory of a fragrant oil in a specialist shop, and the continuity of a practice that stretches back to when these blades were being made for use.
What the name does not tell you, in most cases, is what is actually in the bottle. A mineral oil and a plant-based oil can both be sold as "choji oil" and both perform their basic function — protecting a polished steel surface from atmospheric moisture and oxygen. The differences between them are real but not dramatic, provided both are sword-specific, applied correctly, and replaced regularly.
The most important variable in sword maintenance is not which oil you use — it is whether you maintain the habit. A blade that receives careful attention every three months, with whatever appropriate oil is available, will remain in excellent condition indefinitely. A blade stored with the finest oil and then forgotten for two years will not. Buy good oil. Use it correctly. Do not stop.
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