Milk Firing in Ceramics

Why Milk Firing Works (Porosity + Proteins)

Milk firing (also called milk glazing or “milking”) is a traditional ceramic surface treatment where a bisque-fired piece is soaked or coated with milk (or other dairy products) and then reheated at a low temperature. The goal is to get a warm brown-to-honey color, a soft satin sheen, and reduced absorption. It’s important to be clear from the start: milk firing is not the same as a true glaze. It can make the surface less porous, but it does not create a fully glassy, completely waterproof layer.

The technique works because bisque ware is porous. When you apply milk, it is drawn into the pores like a sponge. During the second, low-temperature heating, the proteins and other organic components in the milk coagulate and partially carbonize, forming a thin film on the surface and inside the upper pores. This film helps “seal” the clay body slightly, so it absorbs water more slowly. If the piece is heated too high, the organic layer starts to burn away, and the effect becomes weaker or disappears. That’s why milk firing depends on a low-temperature refire rather than a hot firing.

Milk firing usually works best on porous, low-fire bodies such as terracotta and other clay bodies that remain absorbent after bisque. It tends to work poorly on very dense, highly vitrified bodies because the milk cannot soak in deeply. In those cases the coating may sit more on the surface and wear off faster. For that reason, the bisque temperature matters: if the bisque is fired too high and the pores close up, the milk effect will be limited. Many makers bisque on the lower end of the recommended range for their clay body to keep the ware absorbent.

You don’t need much equipment: clean, dry bisque pieces, milk (or another dairy product), a container for dipping or a brush/sponge, and a kiln for the refire. Ventilation matters because heating organics produces noticeable odor and fumes. The cleanest, most controlled approach is a ceramic kiln or small electric kiln dedicated to firing, rather than something used for food.

Different dairy products and mixtures can influence the final look. Regular milk gives the classic warm tone. Higher-fat milk often produces a deeper color, but it can also increase the risk of drips, uneven patches, and sticky residue if excess is not removed and the piece isn’t dried properly. Some people use kefir, whey, or cream to vary the tone and texture. A small amount of dissolved sugar is sometimes added to push the color warmer or slightly redder, but it must be fully dissolved; otherwise it can leave tacky spots and stains.

The basic process is simple. Start with clean, fully dry bisque ware – dust and fingerprints can show after firing, so handle carefully. Apply milk by dipping, pouring, or brushing/sponging: dipping is usually the most even, pouring is faster but can leave runs, and brushing gives the most control. Let the excess drain, remove drips, and dry the piece completely. Many makers repeat this 2–3 times (apply, dry, repeat) to deepen the color before the low-temperature refire.

After the piece is dry, it is refired at a low temperature, commonly around 270–350 °C (about 520–660 °F). In this range the organic film sets and darkens. If the temperature is pushed much higher, the organic layer can burn off rather than stabilize. A slow, gentle heat-up is usually safer than a fast ramp. Some makers load the pieces into a cool kiln and warm them together to reduce thermal shock. Good ventilation remains important during this firing because odors can be strong.

Milk firing is also used as a decorative method. If you want a mottled, “alive” surface, you can apply the milk unevenly, vary the thickness, or coat only certain areas. If you want a more refined satin look, milk firing can be combined with burnishing or polishing on bisque; the smoother the surface, the more silky the final sheen can be. The downside is that smoother surfaces also show drips, fingerprints, and uneven coating more clearly, so cleanliness and careful handling matter even more.

The most common problems are fast wear, flaking, and stains. Fast wear usually happens when the bisque is too dense and the milk didn’t penetrate, when the coating was applied too thickly and formed a surface skin, or when the refire was too hot and the organic layer burned away. The fix is to keep the bisque absorbent (within the clay’s safe range), apply thinner coats, dry thoroughly, and stay in a low refire range. Stains and streaks come from drips, dirty ware, fingerprints, and uneven drying. Prevention is mostly technique: clean bisque, remove drips immediately, and dry evenly without rushing.

For use and care, remember that milk firing is not a glaze. It reduces absorption, but it does not fully waterproof the piece. The surface can wear over time, especially if scrubbed with abrasives, washed with harsh detergents, or put in a dishwasher. Gentle hand washing with a soft sponge is best, and long soaking is not ideal. If you need maximum resistance to liquids, acids, and everyday cleaning, a proper fired glaze is still the more reliable option. Milk firing is chosen for its natural warm color, soft tactile feel, and the handmade, organic character it gives to the surface.

From a safety perspective, low-temperature firing of organics produces odors and fumes, so ventilation is essential. It’s generally better to use a kiln that is dedicated to ceramic work rather than an oven used for cooking. Some people attempt low-temperature treatment in household ovens, but it can leave persistent odors and is considered more of a compromise than good studio practice.