Colorants are the oxides and metal compounds added to a glaze to produce color. They’re used in small amounts — typically 0.5–5% of the total dry recipe weight — and they react with the base glaze chemistry, the firing temperature, and the kiln atmosphere to produce their final color. The same colorant can look completely different in different base glazes or different firing atmospheres. Testing is essential.
How Colorants Work
Colorants are metallic oxides or carbonates. In the kiln they dissolve into the molten glaze and the metal ions absorb specific wavelengths of light, producing the colors we see. The key variables that affect the final color are:
Percentage used — more colorant generally means deeper, more saturated color up to a point; beyond that, some colorants go metallic, black, or matte
Base glaze chemistry — the same colorant behaves differently in a calcium-heavy base vs a zinc or barium base
Firing atmosphere — oxidation vs reduction fundamentally changes iron and copper colors
Firing temperature — some colorants fade, shift, or volatilize at high temperatures
Interactions — colorants affect each other when combined; cobalt and iron together produce different results than either alone
The Main Colorants
Iron Oxide (Fe₂O₃ / FeO)
The most versatile colorant in ceramics. In oxidation: yellows, ambers, tans, and browns depending on percentage (1–3% = tan/amber; 5–8% = warm brown; 10%+ = dark brown or black). In reduction: greys, blue-greys, and celadon greens. Iron is also present in many clay bodies and raw materials, contributing background warmth even when not added as a separate colorant. Red iron oxide and black iron oxide produce slightly different results — red iron is more oxidized and gives warmer tones; black iron (FeO) has more immediate color impact at lower percentages.
Cobalt Oxide / Cobalt Carbonate (CoO)
The most powerful colorant — even 0.25–0.5% produces a visible blue. Full saturation is reached around 1–2%; beyond 3–4% the blue goes very dark and can appear almost black. Cobalt carbonate disperses more evenly than cobalt oxide and is preferred for most glaze applications. Pure cobalt blue can read as harsh — combining with small amounts of iron, manganese, or rutile softens and complexifies the color. Cobalt compounds often contain nickel impurities, which can slightly grey or green the blue in certain base glazes.
Copper Oxide / Copper Carbonate (CuO / CuCO₃)
In oxidation: greens ranging from soft blue-green at 1–2% to deep emerald at 3–5%. In reduction: copper red — one of the most prized and difficult effects in ceramics, requiring specific base glaze chemistry and sustained reduction. Copper volatilizes at high temperatures and can affect neighboring glazes in the kiln. Don’t use copper near glazes where contamination would be a problem. Copper carbonate disperses better than copper oxide.
Manganese Dioxide (MnO₂)
Produces purples and browns, often with a speckled quality from coarser particles. Commonly used with cobalt to modify blue toward purple. At high percentages (8%+) manganese can produce metallic, mirror-like surfaces. Manganese is a health concern — wear a dust mask when handling and ensure good studio ventilation. Avoid using manganese in glazes for functional ware that will be used with acidic foods or drinks.
Chromium Oxide (Cr₂O₃)
Produces a stable, opaque green in most base glazes. Unlike most colorants, chromium is relatively unaffected by firing atmosphere. However, it interacts strongly with other colorants — chromium with zinc can produce muddy browns; chromium near tin-opacified glazes in the kiln can produce pink (chrome-tin pink). Keep chromium glazes away from tin glazes in the kiln. Chromium is relatively stable at studio temperatures but handle with care.
Nickel Oxide (NiO)
A modifier rather than a primary colorant — used in small amounts (0.5–2%) to grey, mute, or complexify other colors. Alone it produces greys, grey-greens, and grey-browns depending on the base glaze. Combined with cobalt it greys the blue; with iron it produces subtle warm greys. Nickel is useful for taking the edge off colors that are too saturated or primary-looking.
Rutile (TiO₂ + FeO)
Not a pure colorant — rutile is an impure form of titanium dioxide containing iron. It produces texture, movement, and warm tones rather than clean color. In a glaze, rutile causes variegation — streaks, breaks, and mottling — and adds a warm cream-to-tan quality. Particularly effective over iron-bearing base glazes. At 3–5% rutile produces subtle movement; at 8–10% the surface becomes heavily textured and broken. See: Rutile in Ceramic Glazes.
Tin Oxide (SnO₂)
An opacifier, not a true colorant. At 5–10% tin oxide turns a transparent glaze completely white and opaque. It’s the basis of traditional majolica and delftware. Tin is expensive but produces the cleanest, brightest white of any opacifier. Interacts with chrome in the kiln to produce pink — keep tin glazes and chrome glazes separated.
Mason Stains
Commercially manufactured colorant blends — pre-mixed combinations of metal oxides that produce specific, repeatable colors. More predictable than raw oxides but less flexible. Use in glazes and slips at 5–15%. Always test at your firing temperature — many stains are formulated for specific temperature ranges and fade or shift outside them. See: What Are Mason Stains?
I am a visually impaired ceramic artist. I have been making for around 8 years now. I specialize in functional colorful pottery. Mainly nerikome and other decorative processes.
