Slip CastingEdit

Slip casting is a ceramic forming method in which a slip, a liquid suspension of clay in water, is poured into a plaster mold. The plaster is highly porous and wicks water from the slip, causing a layer of solid material to build on the inner surface of the mold. After the desired wall thickness is achieved, the excess slip is poured out, and the formed shell is left to dry before being removed from the mold. The resulting piece is then bisque-fired and often glazed and fired again to achieve hardness, durability, and a waterproof surface. This technique is especially valued for producing hollow forms with uniform thickness and for enabling rapid production of consistent shapes. Slip (ceramics) Plaster Mold (manufacturing) Ceramics Bisque firing Glaze

History and development

Slip casting emerged in Europe during the early modern period as artisans sought efficient ways to produce consistent tableware and decorative objects. The plaster mold system allowed for mass production and the replication of intricate geometries that were difficult to achieve by hand-building. By the late 19th and into the 20th century, slip casting became a cornerstone of industrial ceramics in many industries, supporting the widespread manufacture of dinnerware, figurines, and sanitaryware. The method complemented other forming techniques such as hand-building, wheel-throwing, and press molding, and it remains a standard process in both traditional craft studios and modern factories. Industrial ceramics Delftware Wedgwood Ceramics Porcelain Stoneware

Process and materials

Materials: The slip is prepared from a suitable clay body dispersed in water of controlled consistency. The clay choice determines color, texture, and shrinkage after firing. Plaster molds are typically made from plaster of paris and are designed to absorb water efficiently to establish a uniform wall thickness. The body may include additives to adjust plasticity, color, and drying behavior. Slip (ceramics) Plaster Clay body Porcelain Stoneware Glaze
Mold preparation: Plaster molds are first dried and sealed to prevent sticking and to control moisture transfer. Multiple-piece molds enable the formation of complex shapes and closed forms. Mold design and surface treatment influence the surface quality of the finished piece. Plaster Mold (manufacturing) Delftware
Casting steps: Slip is poured into the mold and allowed to stand until the inner surface gains the desired thickness. Excess slip is poured back or drained from the mold. The shell is then left to set, carefully removed from the mold, and transferred to drying racks. Variations in timing, slip viscosity, and mold temperature affect wall uniformity and surface texture. Draining (ceramics) Firing (ceramics) Bisque firing
Drying and finishing: After removal, the greenware is dried to a stable moisture content before biscuit firing. Any warping or cracking must be managed during drying. Optional glazing is applied before a final firing to achieve a water-resistant, glossy or matte surface. Greenware Bisque firing Glaze Firing (ceramics)
Quality and defects: Thin or thick spots, pinholes, or distorted shapes can occur if the wall thickness is not controlled or if moisture transfer is uneven. Quality control emphasizes consistent wall thickness, complete drying, and proper mold maintenance. Defects (ceramics) Shrinkage (materials)

Materials and variants

Body compositions: Slip casts can be made from a range of clay bodies, including stoneware, earthenware, and porcelain, each with distinct firing ranges and final properties. The choice affects translucency, strength, and glaze compatibility. Stoneware Earthenware Porcelain
Surface finishes: Glazes applied to slip-cast pieces can vary from glossy to matte, transparent to opaque. Some designers also use underglazes, engobes, or colored slips to achieve decorative effects. Glaze Underglaze Engobe
Industrial and artistic use: Slip casting is used for mass-produced dinnerware and sanitaryware as well as for sculpture and decorative arts. In some cases, automated machines pour and drain slips to further increase production efficiency. Industrial ceramics Ceramic sculpture
Special techniques: Rotational casting and multiple-mlip casting are variations explored in some studios to produce thicker walls or more complex geometries, though the classic method remains pour-and-drain in plaster molds. Rotational casting (ceramics)

Advantages and limitations

Advantages: The method excels at producing hollow, uniform-thickness pieces with intricate internal geometries. It is well-suited for small to medium runs, reduces hand-building labor, and supports reproducibility across many items. It also enables rapid prototyping of new shapes once a suitable mold is created. Uniform wall thickness Mass production
Limitations: The plaster molds are fragile and require careful handling. The initial mold investment can be high, and long-term production benefits depend on mold durability and consistent slip preparation. Complex external textures may require additional surface finishing after demolding. Glaze compatibility and post-firing cracking are concerns that must be managed through formulation and firing schedules. Mold durability Glaze Firing (ceramics)

Innovations and contemporary practice

Modern studios and factories continue to optimize slips, plaster formulations, and mold design to improve strength, shrinkage control, and firing results. Advances in automation and process control, including slip pumps and controlled drainage, help scale production while maintaining precision. The method remains a important part of both traditional craft education and contemporary ceramic manufacturing. Automation (manufacturing) Ceramics education Industrial ceramics