AMACO No. 15-S 1 Gallon Casting Slip Review (2026)

What this slip is and how it is used

AMACO's No. 15-S is a white earthenware casting slip sold pre-mixed and ready to pour directly into plaster molds, which spares a potter the extra step of mixing dry clay powder with water and deflocculant to the right consistency themselves. Slip casting works by pouring this liquid clay into a plaster mold that absorbs water from the slip against its inner walls, building up a solid clay layer before the excess liquid is poured back out, leaving a hollow cast piece behind. Because the slip arrives ready to use, this product suits potters who want consistent, repeatable results without managing their own slip recipe.

Casting behavior and shrinkage

Manufacturer specifications describe the slip as casting quickly with easy release from molds, producing cast shapes that dry with practically no loss and hold their form well before firing. At cone 05, the slip is documented with about 6 percent shrinkage and 14.6 percent absorption, figures that matter for anyone planning a mold designed around a specific finished size, since shrinkage this size needs to be built into the mold dimensions from the start. The slip is also described as non-crazing, meaning fired pieces resist the fine surface cracking that some clay and glaze combinations develop over time.

Firing range

AMACO recommends bisque firing this slip to cone 04, with a glaze firing range spanning cone 06 to cone 02, giving some flexibility in how a studio schedules its kiln loads around other work. That range sits within common low-fire earthenware territory, which is typical for casting slips aimed at decorative and functional small ware rather than high-fire stoneware or porcelain production. Potters should still confirm this firing range matches their own kiln's typical schedule and any glazes they plan to use, since mismatched firing ranges between slip and glaze can cause fit problems on the finished piece.

Safety and what is not included

The product is ACMI certified non-toxic and conforms to ASTM D-4236, the standard covering art materials labeling for potential chronic health hazards, which is worth confirming for a home studio or a classroom setting with less ventilation control than a commercial pottery. Plaster molds themselves are not included with the slip, so buyers need a separate source for molds, whether purchased ready-made or made in-house from plaster and a master model. Because slip settles as it sits, giving the container a thorough stir before each pour is necessary to keep the mix consistent from the first casting to the last.

Who this product suits

This casting slip fits potters and small studios already set up to slip cast, whether producing repeated identical pieces from a single mold or experimenting with mold-made forms alongside wheel-thrown or hand-built work. Someone completely new to slip casting will still need to learn or source plaster molds and basic casting technique separately, since this product solves the slip-mixing step but not the mold-making or casting process itself. For a school or hobby studio already running some casting work, having a ready-to-pour slip on hand removes a time-consuming prep step from an already multi-stage process, freeing up time for finishing and decorating cast pieces instead of measuring and blending powder and deflocculant by hand each time a batch runs low.

Frequently asked questions