a drying schedule

You cannot just blast a wet ceramic with hot dry air and hope — that is the surest way to crack it. Instead you follow a plan that says how warm, how humid, and how fast-moving the air should be at each stage, and how long to hold there, easing the water out at a pace the body can survive. A drying schedule is exactly that recipe: the planned programme of temperature, humidity, air flow, and time used to dry a green body safely and evenly from wet to bone-dry.

A good schedule is shaped around the two drying periods. While the body is still shrinking — the constant-rate period, up to the critical moisture content — it is at its most vulnerable, so the schedule keeps conditions gentle: warm but very humid air, moving slowly, so the surface cannot dry and shrink far ahead of the core. This keeps the moisture gradient shallow and the differential shrinkage small. Once past the critical moisture content — into the falling-rate period, where the particles have touched and shrinkage has stopped — the danger is largely over, so the schedule can safely ramp up: raise the temperature, drop the humidity, and drive out the last, stubbornly-held water quickly. Thicker parts, which have steeper internal gradients, need slower schedules than thin ones.

The drying schedule is where all the physics of drying — capillary stress, differential shrinkage, the two periods — is turned into a concrete set of instructions that a dryer or kiln operator follows. Almost every avoidable drying defect traces back to a schedule that hurried the vulnerable early stage. Industry backs the schedule with hardware: humidity-controlled tunnel and chamber dryers, and for delicate ware, tricks like drying under damp cloths or in slowly-vented enclosures that mimic a gentle schedule. The governing wisdom is simple and hard-won: go slow while it shrinks, then speed up once it does not — the kiln is unforgiving of a schedule that rushes the wet stage.