Slip Casting

Slip Casting Cycle Calculator

Estimate casting time, drain time, demold window, and mold drying time for plaster slip casting.

Updated

mm
weeks
error

Results

calculate

Enter your measurements above and click Calculate.

How Slip Casting Works

Slip casting uses the porosity of plaster molds to extract water from liquid clay slip, building up a wall of uniform thickness against the mold surface. The longer the slip sits in the mold, the thicker the wall. Timing is critical — too short and the piece collapses on demolding; too long and the piece cracks as the clay begins to shrink away from the plaster.

Factors Affecting Casting Rate

Faster Casting

  • New, dry plaster mold
  • Higher slip SG (more solids)
  • Pottery plaster (more porous than Hydrostone)
  • Warmer casting environment

Slower Casting

  • Old or saturated mold
  • Lower slip SG (more water)
  • Hydrostone mold (denser)
  • Cold workshop

Mold Care and Longevity

Allow molds to fully dry between casts — typically 24 hours minimum. Stack molds open-face up in a warm, ventilated area. Never dry molds in a hot kiln; high heat destroys the plaster's crystal structure. A well-maintained pottery plaster mold lasts approximately 100 casts before absorptivity drops significantly.

Frequently Asked Questions

How do I know when the wall is thick enough to drain? expand_more
Observe the slip level dropping — casting stops when the meniscus stops receding. For production work, cut test tiles to verify wall thickness, then time your future pours consistently.
How many casts does a plaster mold last? expand_more
A well-made Pottery Plaster #1 mold typically lasts 50–100 casts before it loses sufficient absorbency. Hydrostone molds can last 150–200+ casts. Store molds dry and avoid contamination with water or soap.
Why must molds dry between casts? expand_more
Plaster can only absorb water when its pores are empty. A saturated mold will not draw water from the slip — the casting process stops. Allow 24 hours minimum drying between casts (or use a drying cabinet with warm air).