Oil-Based Ink

Part of Printing

How to formulate, cook, and grind oil-based printing ink from locally sourced materials.

Why This Matters

Oil-based ink is the chemical foundation of letterpress printing. Unlike water-based writing inks that soak into paper, oil-based printing ink sits on the paper surface, dries by oxidation and polymerization, and produces a dense, permanent impression that resists fading for centuries. The books printed with oil-based ink in the 1450s are still perfectly legible today.

Making printing ink from scratch is achievable in a low-tech context. The two essential ingredients — a carbon-black pigment and a drying oil — are obtainable from widely available materials. The skill lies in knowing which materials work, how to prepare them properly, and how to combine them into an ink that behaves correctly on press.

A community that can make its own ink is not dependent on trade for this critical material. Paper, ink, and a press: these three things together enable the reproduction and preservation of all other knowledge.

Ingredients

The Pigment: Carbon Black

Carbon black is the pigment in virtually all traditional black printing inks. It is chemically pure carbon in very fine particle form, which gives it both its deep black color and its permanence — carbon does not fade, bleach, or react with paper over time.

Lampblack: Made by collecting soot from an oil flame. Burn linseed oil, animal fat, pine tar, or resin in a confined container (a clay pot with a restricted opening works well). Direct the smoke against a cool flat surface — a stone or metal plate — and collect the deposited soot. Lampblack is very fine and produces an extremely deep, velvety black.

Bone black / ivory black: Charred bone ground very fine. Burn bones in a sealed clay container to prevent the carbon from oxidizing away. After cooling, grind the black residue on a stone until the particle size is below visible grit. Bone black has a slightly warmer, brownish-black tone compared to lampblack.

Vine black / charcoal black: Charred grape vines or other wood in sealed containers. Similar to bone black. Adequate for text printing though slightly less opaque than lampblack.

Refining the pigment: For use in printing ink, pigment must be extremely fine — finer than you would think necessary. Coarse particles cause ink to print with a gritty texture, clog fine letterforms, and produce an uneven impression. Grind the pigment on a flat stone with a small amount of oil, working it in a circular motion for 20–30 minutes. The grinding process itself is the purification.

The Vehicle: Drying Oil

The vehicle carries the pigment and, after printing, forms a solid film on the paper surface by oxidative polymerization (exposure to air causes the oil to harden). Not all oils dry — only those with the right chemical composition will work.

Linseed oil: The standard printing ink vehicle. Pressed from flax seeds, linseed oil dries reliably within 12–48 hours when spread in a thin film. It must be processed (cooked or boiled) to improve its drying speed and body.

Walnut oil: Also a drying oil. Used historically for lighter-colored inks because it yellows less than linseed oil. Dries more slowly than processed linseed oil.

Poppy oil: Another drying oil, slower-drying than linseed. Less suitable for production printing but workable.

Non-drying oils (olive oil, vegetable oil, animal fats): These oils will not polymerize and harden — printing made with them will remain sticky indefinitely. Do not use non-drying oils as ink vehicles.

Processing Linseed Oil

Raw linseed oil makes poor printing ink — it is too thin, dries too slowly, and yellows badly. Cooking it improves all three properties.

Boiling (Drying) Oil

1. Pour raw linseed oil into an iron or clay pot to no more than one-third full (oil foams and expands when heated).
2. Heat over a fire to around 200–250°C. The oil will begin to smoke and darken.
3. Maintain heat for 30–60 minutes, stirring occasionally.

Fire risk

Boiling linseed oil is highly flammable and can ignite if overheated or if flames contact the vapors. Work outdoors or in a well-ventilated space. Keep a cover that can be dropped over the pot to smother a fire. Never walk away from boiling oil.

4. After cooking, allow to cool. The oil should be significantly thicker (more viscous) and darker amber in color.
5. For even faster-drying ink, add a small amount of lead or manganese-based drier: litharge (lead monoxide) is traditional — add a small pinch (1–2% by weight) to the hot oil and stir for 10 minutes. Litharge is toxic; manganese dioxide (from certain minerals) is a safer alternative.

Stand Oil

An alternative to boiled oil: linseed oil that is heated in an oxygen-free environment (sealed vessel) at lower temperatures for longer periods. Stand oil has higher body (viscosity), a lighter color, and produces an extremely smooth ink film. More difficult to make but superior for fine work.

Grinding and Mixing the Ink

The Grinding Stone

A flat stone — traditionally marble, granite, or slate — is the mixing surface. It must be fine-grained, hard, and flat. A muller (a flat-bottomed round stone with a handle) is used to grind the pigment and oil together.

Any hard, fine-grained stone with a flat face can substitute. The key is a smooth grinding surface — the grinding motion between muller and slab is what reduces particle size and fully disperses pigment in the oil.

Formulation

For a standard black letterpress ink, start with approximately:

• 1 part lampblack (by weight)
• 2–3 parts boiled linseed oil

This ratio produces a stiff paste. Adjust oil quantity to achieve the correct working consistency (see Ink Consistency).

Grinding Process

1. Place the pigment in the center of the grinding stone.
2. Add half the oil and work into a paste with a palette knife.
3. Add the muller and begin grinding with firm, circular strokes, covering the entire stone surface.
4. After 5 minutes, scrape the ink from the edges back to the center and continue grinding.
5. Assess smoothness: rub a small amount between thumb and finger. Any detectable grit means more grinding is needed. The ink should feel completely smooth — like thick, greasy paint.
6. Add remaining oil gradually while grinding. The ink will soften as more oil is incorporated.
7. Total grinding time for a good ink: 20–40 minutes of active grinding.

Adding Varnish

For a stiffer, more tack ink, add a small amount of heat-bodied oil (varnish) in place of some of the plain boiled oil. Varnish adds body and tack, which improves ink transfer on the press and helps ink sit on top of paper rather than soaking in.

Testing the Finished Ink

Before using new ink on a press run, test it:

1. Consistency test: See Ink Consistency for the finger-test and knife-test methods.
2. Print test: Roll a small amount on the ink disc, ink a form, and pull a single impression. Inspect for clean transfer, sharp edges, no bleed.
3. Dry test: Allow a printed test sheet to dry for 24 hours. The ink should be fully dry (not tacky when touched) and should not come off on a finger rubbed firmly across the print.
4. Adhesion test: The dried ink should resist abrasion — rub the print firmly with a cloth. Good ink stays put; poor ink smears or powders off.

Storing Ink

Oil-based ink oxidizes on exposed surfaces, forming a skin that must be discarded before use. Minimize skin formation by:

• Storing ink in tightly sealed tin cans or ceramic pots.
• Pressing a piece of waxed paper or oiled cloth directly onto the ink surface to exclude air.
• Storing in a cool location (slows oxidation).

Properly stored printing ink lasts for years. Remove any skin formed during storage before using — do not mix it back into the ink body.

Color Inks

While black is the most critical ink for text printing, colored inks can be made from pigments ground in the same oil vehicle:

• Red: Vermilion (mercury sulfide, toxic), red ochre, or madder lake
• Blue: Indigo, azurite (copper carbonate)
• Green: Verdigris (copper acetate), or mix of blue and yellow pigments
• Yellow: Yellow ochre, lead-tin yellow (historic, toxic)

The grinding and vehicle preparation process is identical. Colored inks are used for decorative printing, headings, rubrics (red chapter numbers), and maps.