# The Oil Hewn Shop Notes · https://hewn.build/shop-notes/the-oil AI-drafted, not yet checked: Drafted by Chip, the writing system Hewn runs on Claude, from Hewn's craft corpus. Jonathan Salomons has not read this note yet, and no outside reader has checked it. Read it as a shop note: check a number before you cut to it. Cite as: "The Oil." Hewn Shop Notes, hewn.build/shop-notes/the-oil. Drafted 2026-05-01; AI-drafted, not yet checked. --- The can says "Tung Oil Finish." No tung oil in it. This is normal in the penetrating finish category. The problem is when you're making real decisions — which finish goes on a white oak dining table, what holds up on outdoor cedar — based on what you think is in the can. Here's what's actually in the cans. **Raw linseed oil** is pressed from flaxseed. It penetrates. It cures in weeks. Nobody uses it on furniture anymore because waiting a month between coats is not a reasonable woodworking life. **Boiled linseed oil (BLO)** is raw linseed with metallic driers added — cobalt or manganese naphthenate, typically. Cures in 24–48 hours, inexpensive, widely available. The "boiled" name is historical; they used to heat it, now they add the driers cold. BLO yellows. That's not an opinion, it's chemistry. On dark species — walnut, black locust — it's invisible. On white oak or ash, you'll see it. **Pure tung oil** comes from the tung tree nut. Cures to a harder, more water-resistant film than linseed. Doesn't yellow. Costs more. The cure window is still 24–36 hours per coat in a warm shop. Right choice when color-neutrality matters and you want a genuine penetrating result. **Oil blends** — sold as "Tung Oil Finish," "Danish oil," "finishing oil" — contain some mix of oil (tung, linseed, or soy), solvents for penetration, and an oil-based varnish for durability. They cure faster than pure oils because of the varnish component. More forgiving to apply, more durable than straight oil, but they sit in the middle: not as tactile as pure oil, not as protective as a real film finish. The label usually won't tell you the ratios. The practical upside of this middle-ground position is real — faster cure, easier application, good enough durability for most indoor furniture. That's a reasonable trade for a working shop. --- **BLM for outdoor work** BLM is not a product. It's a field-mixed formula: one part boiled linseed oil, one part mineral spirits, first coat. Straight BLO for subsequent coats. The mineral spirits thin the first coat so it penetrates end grain and open-pored species before the surface saturates. After that, you don't need the thinning. Outdoor furniture gets BLM for three reasons. BLO is cheap, and outdoor pieces need regular reapplication — the economics of a commercial oil blend add up over years. The field-mix ratio gives you control over penetration on dense or complex-profile pieces. And BLO is available everywhere, which keeps the maintenance story simple. The trade: BLO yellows, and UV accelerates it. On dark species, nobody cares. On white oak benches or ash chairs, warmth accumulates over time. You decide whether that's acceptable before you open the can. --- **Application** Penetrating oils go on with the flood-wipe method. Apply more than the wood will absorb. Get every surface wet. Let it sit 15–30 minutes — watch for the wet-shiny surface to go dull-looking, which means the wood is close to saturation. Then wipe off all the excess. Thoroughly. Every surface. Change rags when they're saturated. The surface should feel dry-to-tacky, not wet. The wipe-off step is where most people go wrong. Oil sitting on top of the wood rather than inside it doesn't cure the same way. It stays tacky, picks up dust, goes gummy. More coats don't fix a bad wipe-off. Let each coat cure fully before the next. Minimum 24 hours in a warm shop. In a cold BC Interior shop in November, that number doubles or triples, and below 5°C the oxidation reaction that cures the oil essentially stops. Bring the piece inside to cure, or heat the shop. More coats over uncured oil just makes things worse. --- **The rag disposal problem** This one isn't optional information. Oil-soaked rags are a spontaneous combustion hazard. The oxidation reaction that cures the oil generates heat. A balled-up rag in a corner can reach ignition temperature in a few hours. This has burned down shops. It has killed people. Spread rags flat — outside, or on a non-flammable surface with airflow — until fully cured (stiff and dry). Or submerge them immediately in water in a metal container with a lid. Either method works. What doesn't work is leaving them crumpled on the bench. Doesn't matter how many years you've done it without incident. --- **The decision** Pure tung oil: color-neutral, tactile, slow cure. Right for fine indoor furniture on light species. Oil blend: faster cure, more durable, easier application. Good default for most furniture. BLO / BLM: economical, right for outdoor work or species where yellowing is acceptable or invisible. All three are penetrating finishes. They share the same virtues — tactile result, easy repair, forgiving application — and the same limits: limited protection, require reapplication, won't hold up on a wet surface. The choice within the category is color, cure time, and cost. Know what's in the can before you open it.