German Stoneware: An Art of the Everyday. (2012). Philadelphia Museum of Art Bulletin, 6, 4–60. http://www.jstor.org/stable/44782816 (pages 7-9)

In the 1500s Cologne’s advanced pottery production moved to Raeren and Siegburg due to air quality and fire restrictions. As production increased and new potters arrived, ornamentation methods were further developed. Some firmer more pliable clays were used to sculpt low-relief designs and applied to the vessel using slip (a process still used today).

Sandstone molds were also used to create more intricate decorations. First the artist (not necessarily a potter, but another skilled artisan) would carve the sandstone to create an initial mold, a positive would be made of clay and then fired to a hardened state. That positive would be added to clay again to create a final negative and consistent mold to be used repeatedly. The decoration would then be added to the vessel using slip and may be combined with other reliefs. Stamps and tools were also used to create patterns through carving. This was done to compliment the molded reliefs or on their own.

In the later 16th century, in addition to unique firing techniques and slip coverage resulting in the brown clay appearance, potters began using cobalt to provide a blue tint to the clay. This is a standout feature of Raeren pottery from the 16th century to 19th century. Many of these techniques are still used today for decorating pottery; however, the cobalt and addition of salt glaze is not as common for safety concerns. Today, other methods for glazing are used with a wider variety of colors and application methods.