How Sancai Glaze Is Made in Tang Ceramics

How Sancai Glaze Is Made in Tang Ceramics

Why does a Tang dynasty horse figure show streaks of green, amber, and cream running into each other like watercolor on wet paper? Museum visitors often assume the effect was painted on. It wasn’t. The blending happens because of chemistry, not brushwork. Sancai glaze is a low-temperature lead glaze system that relies on metal oxide colorants and gravity during firing to produce its signature mottled surface.

What “Sancai” Actually Means and Why the Process Matters

Sancai translates roughly to “three colors,” though pieces often show more than three hues once colorants mix on the surface. The term describes a glazing method, not a fixed palette. A piece described as “sancai-style” might use modern glaze formulas that mimic the look without the same lead-flux chemistry or firing behavior.

The technique originated during the Tang dynasty (618–907 CE) and was applied mainly to earthenware — tomb figures, dishes, pillows, and architectural elements. The body clay was fired first at a higher temperature to harden it, then coated with glaze and fired again at a much lower temperature. This two-stage approach is central to why the colors behave the way they do.

The Low-Fire Lead-Glaze Process, Step by Step

This is the section most people researching sancai actually need, because the “three colors” are not three separate paints. They come from a shared glaze base reacting differently depending on which metal oxide is added. Here’s what happens at each stage:

1. Bisque firing the clay body. The earthenware form is fired once to a moderate temperature to remove moisture and give the piece enough strength to handle glazing without collapsing.
2. Preparing the lead-flux glaze base. A lead oxide flux is mixed into a silica-based glaze. Lead lowers the melting point dramatically, which is why this is called a low-fire glaze process rather than a stoneware-range glaze. Without the lead flux, these colors would not develop at such comparatively low kiln temperatures.
3. Adding metal oxide colorants. Copper, iron, and manganese are mixed separately into batches of the same base glaze, then applied to different areas of the piece — sometimes brushed, sometimes dipped or poured in bands.
4. Second firing at low temperature. During this firing, the lead flux melts and becomes fluid. Because the glaze is genuinely liquid at this stage (not just softened), the colored sections run and bleed into each other, especially on vertical surfaces like a vase neck or a horse’s flank.
5. Cooling and settling. As the kiln cools, the glaze solidifies in place, locking in the drips, pooling, and color gradients that make each piece unique.

What Each Colorant Actually Does — and What Goes Wrong If You Get It Wrong

The colors are not interchangeable design choices — each oxide behaves differently in a lead-based melt, and getting the ratio or firing wrong changes the entire surface outcome.

Colorant	Resulting Color	What It Affects in Practice	Common Mistake
Copper oxide	Green	Produces the brightest, most fluid color in the glaze; tends to migrate furthest during firing because of how readily it interacts with the lead flux	Overloading copper causes the green to bleed too far, muddying adjacent amber or cream zones
Iron oxide	Amber / brown-yellow	Gives the warm ochre and honey tones; generally more stable and less prone to excessive running than copper	Using iron-rich clay bodies without adjusting glaze thickness can create uneven, blotchy amber patches
Manganese oxide	Cream / pale brown	Creates the softer neutral tones that anchor the palette and keep the green and amber from looking harsh	Too little manganese leaves no neutral base, making the piece look unbalanced or overly saturated

Firing temperature control is the other variable that separates skilled work from careless work. Fire too hot, and the lead glaze becomes so fluid that all three colors collapse into a muddy wash, losing the distinct color separation often seen on sancai ceramics. Fire too cool, and the glaze stays underdeveloped — dull, matte, and patchy rather than glassy. This is also why Tang-style pieces show pooling at the base: gravity pulls the melted glaze downward during the firing, and a heavier bead of glaze at the foot is a visual sign of the low-fire process rather than a cooler modern glaze brushed on for effect.

Reading a Piece: A Practical Checklist

Whether you’re a student examining a museum piece or a traveler viewing sancai ceramics, here’s what to check:

• Glaze pooling at the base. Genuine low-fire lead glaze runs downward and thickens near the foot. A perfectly even glaze coat from top to bottom often signals a different, non-traditional glazing method.
• Color bleed patterns. Look for soft, organic blending between green, amber, and cream — not hard-edged painted borders.
• Craquelure (fine surface cracking). Lead glazes often develop a fine crackle network as they cool, caused by the mismatch in shrinkage rates between glaze and clay body.
• Surface sheen. A properly fired lead glaze has a glassy, slightly wet-looking shine. Chalky or flat surfaces suggest underfiring or a substitute glaze formula.

Common Misconceptions About Sancai Ceramics

A few recurring mistakes can make it difficult to understand sancai-style ceramics in museum displays and collections:

• Assuming brighter colors mean higher quality. Overly vivid, uniform coloring often points to modern ceramic glazes designed to visually reference sancai without replicating the lead-flux firing behavior.
• Ignoring the clay body. Authentic Tang-style ware uses earthenware, which is more porous and less dense than stoneware or porcelain. A heavy, dense body with sancai-style coloring is a mismatch worth questioning.
• Overlooking safety context. Traditional sancai glazes used lead as a flux. Reproductions intended for food contact or children’s use should be evaluated separately from decorative or display pieces, since lead-glazed surfaces are historically not intended for functional tableware.
• Treating “three colors” literally. Some pieces legitimately show only two dominant colors, or additional colorants like cobalt for blue accents, depending on the region and period. Rejecting a piece for not showing exactly three colors misunderstands the term.

For further general background on Tang dynasty material culture and trade, museum and academic references remain the most reliable starting point for understanding the historical context of sancai ceramics.