Oil Binder

Part of Pigments and Paint

Making linseed oil and other drying oil binders for paint and protective coatings.

Why This Matters

Drying oils are the foundation of the most versatile and weather-resistant paints available from natural materials. Unlike water-based binders that dissolve in rain or egg-based binders that can be damaged by moisture, oil-bound paints form a tough, flexible, waterproof film that protects surfaces for years. Before synthetic paints existed, every wooden ship, every exterior building surface, and every piece of outdoor equipment was protected by oil-based coatings.

For a rebuilding community, drying oil production is essential for infrastructure protection. Wood exposed to weather rots within years without coating. Metal rusts. Masonry absorbs water and spalls in freeze-thaw cycles. Oil paints and finishes prevent all of these failures, extending the useful life of buildings, tools, and equipment by decades.

The primary drying oils — linseed (from flax), walnut, and poppy seed — are all produced from plants that can be cultivated in temperate climates. A single acre of flax can produce enough linseed oil to coat a substantial building. Once you establish the crop, you have an indefinite renewable supply of the most important protective coating chemistry available.

Drying Oil Chemistry

Not all oils dry. Cooking oils like olive oil and animal fats remain liquid or sticky indefinitely. Drying oils undergo a chemical transformation called oxidative polymerization — exposure to air causes the oil molecules to cross-link, forming a solid, flexible polymer film.

The key factor is the iodine value — a measure of chemical unsaturation (double bonds) in the oil. Higher iodine values mean faster, harder drying:

Oil	Iodine Value	Drying Speed	Film Quality
Linseed	170-200	Fast (2-5 days)	Hard, tough, yellows slightly
Walnut	140-160	Medium (3-7 days)	Hard, less yellowing
Poppy seed	130-145	Slow (5-10 days)	Flexible, minimal yellowing
Hemp seed	145-170	Medium-fast	Similar to linseed
Tung (wood oil)	160-175	Very fast (1-2 days)	Extremely hard, water-resistant
Sunflower	120-140	Slow-medium	Soft film, poor durability

Linseed oil is the standard for paint binders because it dries quickly, forms a very hard film, and is widely available. Walnut oil is preferred for white and light-colored paints because it yellows less.

Extracting Linseed Oil

Growing Flax for Oil

Oil flax (Linum usitatissimum) is the same plant as fiber flax but is grown differently:

• Sow in spring, 10-15 cm spacing (closer for fiber, wider for seed)
• Full sun, moderate water
• Harvest when seed bolls are brown and dry (late summer)
• Cut plants, dry in sheaves, then thresh to separate seeds
• One acre yields approximately 10-15 bushels of seed, producing 50-75 liters of oil

Cold Pressing

Cold-pressed linseed oil is the highest quality for paint:

1. Clean the seeds — remove chaff, stems, and debris
2. Crush seeds in a mortar or between flat stones to crack the hulls
3. Place crushed seeds in a strong cloth bag
4. Press the bag in a screw press, lever press, or between weighted boards
5. Collect the golden-amber oil that drains out
6. Let the oil settle for several days in a covered container
7. Decant the clear oil off any sediment (mucilage and seed debris)

Yield

Linseed is approximately 35-40% oil by weight. Expect to recover about 25-30% in practice due to oil retained in the press cake. One kilogram of seed yields roughly 250-300 ml of oil.

Hot Pressing (Higher Yield)

Heating the crushed seeds before pressing increases yield at the cost of slightly lower quality:

1. Crush seeds as above
2. Warm gently in a pan — do not exceed 60 degrees Celsius
3. Press while warm
4. This method extracts 10-15% more oil
5. The oil is darker and may contain more impurities — settle and filter carefully

Boiling Method (No Press Available)

If you lack a press:

1. Crush seeds thoroughly
2. Place in a pot and cover with water
3. Simmer gently for 2-3 hours, stirring occasionally
4. The oil rises to the surface and floats on the water
5. Let cool, then skim the oil layer off the top
6. This method is less efficient but requires no special equipment

Processing Oil for Paint Use

Raw linseed oil dries slowly and unevenly. Processing improves its performance as a paint binder.

Stand Oil (Heat-Bodied Oil)

Stand oil is linseed oil thickened by heating in the absence of air. It produces the smoothest, most durable paint films:

1. Pour raw linseed oil into a deep, narrow container (to minimize surface area)
2. Heat to 280-300 degrees Celsius — this requires a sustained hot fire
3. Maintain temperature for 8-12 hours, stirring occasionally
4. The oil thickens significantly, becoming honey-like in consistency
5. Cool and store in sealed containers

Fire Hazard

Linseed oil at high temperatures produces flammable vapors. Heat outdoors, away from structures. Never heat over an open flame — use a sand bath or enclosed kiln. Keep a lid ready to smother any fire.

Sun-Thickened Oil

A safer alternative to heat processing:

1. Pour raw oil into shallow trays (ceramic or glass)
2. Cover with glass or thin fabric to keep out debris while allowing air exposure
3. Place in direct sunlight
4. Stir daily
5. Over 2-4 weeks, the oil thickens and becomes paler (bleached by UV light)
6. Sun-thickened oil dries faster and yellows less than raw oil

Boiled Oil (with Driers)

Historically, “boiled” linseed oil was heated with metallic driers to accelerate drying:

1. Heat raw linseed oil to 130-150 degrees Celsius
2. Add a small amount of metallic drier — historically lead oxide (litharge), but manganese dioxide is less toxic
3. Maintain temperature for 2-3 hours while stirring
4. The metallic compound dissolves into the oil and catalyzes faster oxidation
5. Cool, settle, and decant

The metallic driers reduce drying time from 3-5 days to 12-24 hours. Lead-based driers are toxic; use manganese if available.

Walnut Oil

Walnut oil is extracted from ripe walnuts and is the preferred binder for white and pale-colored paints because it yellows far less than linseed oil.

Extraction

1. Shell ripe walnuts and remove the nutmeats
2. Crush thoroughly in a mortar
3. Warm gently and press, or boil in water and skim
4. Settle and filter the oil

Walnut oil dries more slowly than linseed — allow 5-7 days between coats. It produces a softer film but with better color retention.

Other Drying Oils

Poppy Seed Oil

• Extracted by pressing poppy seeds
• Very pale, minimal yellowing
• Slow drying (7-10 days)
• Produces a soft, flexible film
• Best for whites and blues where yellowing is unacceptable

Hemp Seed Oil

• Extracted from hemp seeds by pressing
• Similar to linseed in drying properties
• Slightly greenish tint — filter and sun-bleach if possible
• Good general-purpose alternative to linseed

Tung Oil

• Extracted from tung tree (Aleurites fordii) nuts
• Extremely fast drying and exceptionally water-resistant
• Produces a distinctive wrinkled texture if applied too thick
• Best applied in very thin coats
• Limited geographic availability (warm climates)

Storage and Handling

Storage

• Store in full, sealed containers — minimize air contact to prevent premature skinning
• Glass or glazed ceramic containers are best
• Oil stored properly keeps for years
• If a skin forms on stored oil, carefully remove it and the oil beneath is still usable

Spontaneous Combustion Warning

Critical Safety

Rags, cloths, and brushes soaked with drying oil can spontaneously catch fire as the oil oxidizes. The oxidation reaction generates heat, and crumpled oily rags trap the heat until ignition temperature is reached. ALWAYS spread oil-soaked rags flat to dry in open air, or submerge them in water. Never pile or crumple oily rags. This is a real and serious fire hazard.

Cleaning

• Clean brushes and tools with turpentine (distilled from pine resin) or with a strong lye solution
• Soap and water will not remove drying oil
• Clean tools immediately after use — dried oil is extremely difficult to remove

Quality Testing

Test your oil before committing to a large paint batch:

1. Clarity test: Good oil should be clear and golden, not cloudy or dark
2. Drying test: Apply a thin film to glass. It should become touch-dry within 3-5 days (raw) or 12-24 hours (boiled/processed)
3. Film test: The dried film should be hard, glossy, and not tacky. It should resist scratching with a fingernail
4. Flexibility test: The dried film should bend without cracking when the substrate is flexed