Oil Paint

Part of Pigments and Paint

Making oil paint from scratch using drying oils and ground pigments.

Why This Matters

Oil paint is the most versatile and durable paint formulation achievable with pre-industrial technology. It adheres to wood, metal, stone, plaster, canvas, and leather. It resists water, sunlight, and temperature extremes. It can be applied in transparent glazes or thick opaque coats. For five centuries it dominated both fine art and practical coating technology because nothing else matched its combination of workability and durability.

For a rebuilding community, oil paint serves as the primary protective coating for all exterior surfaces. Wooden structures without paint deteriorate in 10-20 years; painted structures last 50-100 years or more. Metal tools and fittings without coating rust to uselessness; oil paint stops corrosion. Boats, bridges, water equipment, and any surface exposed to weather require oil-based protection.

Making oil paint requires only two components: finely ground pigment and drying oil. The process is straightforward — grind the two together until smooth. The skill lies in getting the ratios right, achieving proper consistency, and understanding how different pigments behave with different oils.

Materials Needed

Pigments

Any finely ground pigment can be used in oil paint. The pigment must be ground to fine powder before mixing with oil (see Grinding Techniques).

Drying Oil

Linseed oil is the standard. Walnut oil is used for light colors. See Oil Binder for oil extraction and processing.

Additional Materials

Material	Purpose	Source
Turpentine	Thinner, solvent	Distilled from pine resin
Beeswax	Thickener, matte finish	Beekeeping
Metallic driers	Speed drying	Manganese dioxide, lead oxide
Chalk/whiting	Extender, body	Ground limestone

The Mulling Process

Making oil paint is called “mulling” — grinding pigment into oil on a flat surface.

Step-by-Step

1. Prepare the surface: Place a clean, flat slab (glass, polished stone, or marble) on a stable table at working height

2. Mound the pigment: Place 2-3 tablespoons of finely ground, dry pigment on the slab

3. Create a well: Make a crater in the center of the pigment mound

4. Add oil: Pour a small amount of drying oil into the well — start with approximately half the volume of the pigment. Different pigments absorb different amounts of oil

5. Incorporate: Using a palette knife (or flat-bladed knife), fold the pigment into the oil. Work from the outside edges inward, drawing dry pigment into the wet center

6. Mull: Once roughly mixed, use a muller (flat-bottomed grinding stone) to grind the mixture. Apply firm pressure and work in circular motions, covering the entire slab area

7. Scrape and repeat: Every 30-60 seconds, scrape the paint back to the center of the slab with the palette knife, then continue mulling

8. Test consistency: After 10-15 minutes of mulling, lift the muller. The paint should be smooth, creamy, and free of grit. It should hold a soft peak when pulled up with the knife

9. Adjust: If too stiff, add oil drop by drop. If too runny, add more pigment. The ideal consistency resembles thick cream or soft butter

Oil Absorption

Different pigments absorb vastly different amounts of oil. Earth pigments (ochres) absorb moderately. Carbon black absorbs heavily (needs lots of oil). Lead white absorbs little. Start with less oil than you think you need — you can always add more, but you cannot remove it.

Oil Absorption Rates

Pigment	Oil Absorption (ml oil per 100g pigment)	Notes
Lead white	12-15	Very low — stiff paint
Chalk white	40-50	High absorption
Yellow ochre	25-35	Moderate
Red ochre	20-30	Moderate
Burnt sienna	40-50	High
Raw umber	30-40	Moderate-high
Lamp black	100-120	Extremely high
Malachite	20-25	Low

Modifying Paint Properties

Thinning

Oil paint as mulled is typically too thick for direct application. Thin with:

• Turpentine: Evaporates as the paint dries, leaving only pigment and oil. Produces a matte finish in thin applications. Best for underpainting and first coats
• More oil: Makes paint glossier and more transparent. Slower drying. Best for final coats and glazes
• Turpentine + oil blend: The standard medium. Mix 1 part oil with 1-2 parts turpentine. Balances drying time, gloss, and flow

Thickening

For impasto (thick application) or gap-filling:

• Add more pigment during mulling
• Mix in a small amount of melted beeswax (2-5% by volume) — this also gives a matte, waxy finish
• Use stand oil (heat-bodied oil) which is naturally thicker

Drying Time Adjustment

To speed drying:

• Add a trace of metallic drier (manganese dioxide powder mixed into the oil)
• Use boiled linseed oil instead of raw
• Apply thinner coats — thick oil paint can take weeks to dry
• Expose to warm, dry, well-ventilated conditions

To slow drying (more working time):

• Use poppy seed oil or walnut oil instead of linseed
• Add a drop of clove oil — this retards oxidation
• Work in cool, humid conditions

Application

Surface Preparation

Oil paint requires proper surface preparation for adhesion and durability:

Wood:

1. Sand smooth and remove dust
2. Apply a primer coat — oil paint thinned 50% with turpentine, or a coat of pure oil
3. Let primer dry completely (2-3 days)
4. Apply paint coats

Metal:

1. Remove all rust and scale by scraping and sanding
2. Apply immediately — bare metal begins rusting within hours
3. First coat should be thinned to penetrate the surface
4. Red lead primer is traditional but toxic. Red ochre in oil is a safer alternative

Plaster/Masonry:

1. Surface must be fully cured and dry
2. Apply a coat of diluted oil as a sealer
3. Let sealer dry completely
4. Apply paint coats

Painting Technique

1. First coat (primer): Thin the paint significantly (2 parts turpentine to 1 part paint). This coat penetrates the surface and provides grip for subsequent layers. Apply thinly and evenly. Dry for 2-3 days

2. Second coat (undercoat): Use paint at medium consistency (1:1 turpentine to paint). Build up coverage and color. Dry for 2-3 days

3. Final coat (topcoat): Use paint at full strength or thinned slightly with oil (not turpentine) for a glossy, durable finish. Apply evenly — this is the weather-facing surface

Fat Over Lean Rule

Each successive layer should contain more oil than the previous one. This is the “fat over lean” principle. If a lean (turpentine-heavy) layer is applied over a fat (oil-heavy) layer, the top coat dries and shrinks before the bottom coat, causing cracking. First coats: more turpentine. Later coats: more oil.

Brush Selection

• Stiff bristle brushes (hog hair, or stiff plant fiber) for thick paint and coverage
• Soft brushes (squirrel, badger, or fine hair) for smooth finishes and detail
• Clean brushes in turpentine immediately after use
• For large surfaces (walls, hulls), use wide flat brushes or even rags wrapped around a pad

Storage

Storing Mixed Paint

Oil paint can be stored for weeks to months if air is excluded:

1. Pack the paint into a container, pressing out air pockets
2. Smooth the surface flat
3. Pour a thin layer of oil or water over the surface to seal it from air
4. Cover tightly
5. If a skin forms on stored paint, carefully peel it off — the paint beneath is still usable

Long-Term Pigment Storage

For convenience, pre-mull pigments into thick paste (slightly more pigment than usual) and store in sealed containers. Thin to working consistency with oil and turpentine at the point of use. Pre-mulled paste stores better than fully thinned paint.

Troubleshooting

Problem	Cause	Solution
Paint won’t dry	Too thick, or no drier	Apply thinner; add metallic drier
Paint wrinkles	Top dried before bottom (too thick)	Apply thinner coats; sand and repaint
Paint cracks	Lean over fat (wrong layer order)	Follow fat-over-lean rule; sand and start over
Paint yellows	Normal for linseed oil, especially in dark areas	Use walnut or poppy oil for light colors; expose to light
Paint is gritty	Pigment not ground fine enough	Re-mull with more grinding time
Poor coverage	Too much oil, not enough pigment	Add more pigment during mulling
Paint chalks/powders	Insufficient binder	Add more oil; re-coat

Safety

• Turpentine: Flammable and toxic if inhaled in quantity. Use outdoors or with ventilation
• Spontaneous combustion: Oil-soaked rags are a serious fire hazard. Spread flat to dry outdoors or submerge in water. Never crumple or pile
• Lead pigments: If using lead white or red lead, avoid skin contact and inhalation. Work outdoors. These pigments produce the best oil paint but are cumulative poisons
• Metallic driers: Manganese and lead compounds are toxic. Use sparingly and handle with care