Drying and nondrying oils
The Forest Products Laboratory sorts oils by whether they cure. Drying oils — tung, linseed and walnut among them — soak in and react with air to harden, forming a barrier to liquid water; they can take several weeks to cure fully. Nondrying oils, vegetable or mineral, soak in but never harden. Both are penetrating finishes: they leave no film to peel, and worn areas can be patched without lap marks, the Laboratory notes. Films, it adds, are easier to clean and can better protect the wood from scratches and dents. How the two kinds of finish compare is in wood finish types.
Five things sold as oil
| Sold as | Example | What the maker says it contains | Dry / recoat |
|---|---|---|---|
| Drying oil | Tung, linseed or walnut oil | The oil alone | May take several weeks to cure (FPL) |
| Boiled linseed oil | Sunnyside | Linseed oil with cobalt and manganese driers | Not stated in the data sheet |
| Danish oil | Watco | Drying and semi-drying oils, rosin ester, mineral spirits — 'oil & varnish' | Touch 6–8 h; handle 10 h; recoat 72 h |
| Tung oil finish | Minwax | Tung oil alkyd resin, driers, additives, mineral spirits | Not stated in the data sheet |
| Hardwax oil | Osmo Polyx-Oil | Plant oils, waxes, paraffin, driers, white spirit | About 8–10 h between coats |
Watco's times are at 70–80°F and 50% RH; Osmo's at 23°C and 50% humidity. 'Not stated' means the document reviewed gives no time.
- Boiled linseed oil is not boiled oil alone: Sunnyside describes its product as flaxseed oil with additives to shorten drying, and its safety data sheet names the drier — a cobalt manganese salt. Sunnyside says to use it on unfinished wood only, thinned with up to two parts mineral spirits.
- Danish oil from Watco is, in Watco's words, a blend of penetrating oil and varnish that hardens in the wood. Its instructions stress wiping off all the excess after 15 minutes.
- 'Tung oil finish' from Minwax is, by its data sheet, a tung oil alkyd resin with driers in mineral spirits that dries to a protective coating — a varnish made with tung oil, not tung oil alone. Do not assume a label with 'tung' in it is the pure oil.
- Hardwax oil such as Osmo's Polyx-Oil combines plant oils with waxes; Osmo applies two thin coats and says no sanding between them is needed.
Which of them suits a given piece is the subject of choosing a finishing oil.
Applying an oil
The makers' common thread is thin application and wiping off what the wood does not take. Watco says that removing all the excess is essential for proper drying and for any topcoat to stick, and allows a polyurethane over its oil after at least 72 hours; Osmo says that applying its oil too generously, or with too little ventilation, delays drying. Sunnyside thins its linseed oil so it penetrates. For colour first, see wood stain; for the general method, finishing techniques.
Safety— Oily rags can catch fire on their own
NFPA explains that the oils in oil-based finishes release heat as they dry; in a pile of rags the heat builds until it ignites. The makers' instructions differ: Sunnyside's safety data sheet says to keep soaked materials in sealed metal containers; Osmo says to wash used cloths immediately or keep them in an airtight container; NFPA says to dry rags outside, spread out and away from buildings, then store them in a metal container with a tight lid filled with water and detergent. Follow the product's label and your local fire service.
Finishing items that touch food is a separate question with its own limits — see food-safe wood finishes.
Using an oil finish
- The data sheet read, to know what the product actually is
- Bare wood, sanded to the maker's grit
- Thin coats, with all excess wiped off
- The maker's time between coats, and before any topcoat
- A plan for rags before the can is opened
- Good ventilation while it dries
Sources
Compositions are each maker's own statement, from its data sheet or safety data sheet; percentages are not published and are not estimated. Times are the maker's at the conditions given. Products sold under use names such as teak oil or butcher block oil were not reviewed and are not described.
- 1.
Christopher G. Hunt. Wood Handbook: Wood as an Engineering Material (FPL-GTR-282), Chapter 16: Finishing Wood. USDA Forest Service, Forest Products Laboratory, 2021.
Used for: Drying oils such as tung, linseed and walnut penetrating and curing to resist water, and possibly needing several weeks to cure; nondrying vegetable and mineral oils not curing; penetrating finishes leaving no film to peel; makers not sharing standard definitions.
- 2.
Mark Knaebe. Finishes for Wood Bowls, Butcher Blocks, Other Items Used for Food, and Children's Toys (FinishLine). USDA Forest Service, Forest Products Laboratory, 2013.
Used for: Drying oils (linseed, tung and diluted varnish) also called wood sealers, patchable without lap marks.
- 3.
21 CFR 175.300, Resinous and polymeric coatings. U.S. Food and Drug Administration, Code of Federal Regulations (2025 edition), 2025.
Used for: Tung (Chinawood), linseed and walnut listed among the drying oils.
- 4.
Technical Data Sheet 872, Boiled Linseed Oil. Sunnyside Corporation, 2010.
Used for: Boiled linseed oil as flaxseed oil with additives to shorten its drying time, for unfinished wood only, thinned up to 2:1 with mineral spirits.
- 5.
Safety Data Sheet, Boiled Linseed Oil (87216). Sunnyside Corporation.
Used for: The drier as 'linseed oil, cobalt manganese salt', and oil-soaked rags that may spontaneously ignite, to be kept in sealed metal containers.
- 6.
Technical Data WAT-02, Watco Danish Oil. Rust-Oleum (Watco), 2020.
Used for: Danish Oil as 'a unique blend of penetrating oil & varnish' of drying and semi-drying oils and rosin ester in mineral spirits; 15 minutes' penetration, all excess wiped off; 6–8 h to touch, 10 h to handle and 72 h to recoat at 70–80°F and 50% RH; polyurethane over it after at least 72 hours.
- 7.
Technical Data Sheet, Minwax Tung Oil Finish. Minwax.
Used for: Tung Oil Finish as tung oil alkyd resin, driers and additives in mineral spirits, curing by solvent evaporation and reaction with oxygen into a protective coating.
- 8.
Product Information, Polyx-Oil Original. Osmo, 2020.
Used for: Polyx-Oil as plant oils and waxes with paraffin, driers and dearomatised white spirit; two thin coats about 8–10 hours apart at 23°C and 50% humidity; 24 m² per litre per coat on smooth wood; used cloths washed at once or kept airtight because of self-ignition.
- 9.
Safety with Oily Rags (safety tip sheet). National Fire Protection Association, 2019.
Used for: Oils in oil-based finishes releasing heat as they dry, and NFPA's procedure for oily rags.
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