In-glaze — decorative technique used in ceramics, specifically on an unfired tin-glazed surface. It involves painting the desired design onto the surface before the firing process. As the ceramic piece is fired in the kiln, the in-glaze decoration sinks into the tin glaze, creating a seamless fusion between the design and the glaze.

This technique allows for intricate and detailed designs to be applied to the ceramic surface. The unfired tin glaze provides a smooth base for the in-glaze decoration, ensuring that the design adheres well to the surface during the firing process. As the piece undergoes high temperatures in the kiln, the glaze melts and flows, incorporating the in-glaze decoration into its layers.

The result is a decorative effect where the design becomes an integral part of the glaze, creating a harmonious and unified appearance. The sinking of the decoration into the tin glaze during firing adds depth and permanence to the design, ensuring its longevity and durability.

In-glaze decoration has been used throughout history in various ceramic traditions, including MAJOLICA, FAIENCE, and tin-glazed EARTHENWARE. It is a technique that requires skill and precision, as the artist must carefully apply the decoration before firing, taking into account the desired outcome and the interaction between the design and the glaze.