Raku and the beauty of the unexpected: The Resist Slip Technique
In the world of ceramics, some of the most captivating effects are born from happy accidents. One such discovery is the resist slip technique, developed from an observation made during Raku firings, where raku glaze unexpectedly chipped off pots and acted as a resist, preventing the smoke from penetrating the body and revealing a network of crackle lines. Tim Andrews explored and refined this approach, turning it into an intentional and expressive decorative method.
The essence of the resist slip technique lies in creating a barrier between the clay surface and the glaze. When fired in the Raku process, the glaze typically prevents smoke from entering the clay body—except through its network of fine cracks. These cracks allow smoke to penetrate, leaving carbonised lines on the surface. By applying a refractory slip layer before glazing, potters can create a removable glaze mask, producing rich, smoky effects after the glaze is peeled away post-firing.
The resist slip must be carefully formulated. It should stay on the pot well enough to survive glazing and firing, but not so much that it becomes impossible to remove. Materials like china clay, quartz and alumina are commonly used, since they resist melting at Raku temperatures. Surface preparation is also key—burnishing or applying terra sigillata before the bisque firing can make glaze removal easier and cleaner.
The real magic of the resist slip technique comes from its balance of control and unpredictability. Some potters, like David Roberts, manipulate the process further by drawing lines into the unfired glaze, guiding where smoke will enter. Others, like Andrews, experiment with masking tape, wax, or even bubbles in the glaze, embracing both the planned and the unpredictable. In the end, the most successful pieces emerge when the artist works with the natural tendencies of the materials—inviting randomness to take part in the final design.
*This information is based on Raku, by Tim Andrews..
Join us for our Raku - From Clay to Fire Course.
An immersive journey guided by Tim Andrews at Cerdeira - Home for Creativity.