sun pan
A vat used for drying slip (a thin, slippery mix of clay and water), sometimes with artificial heat.
sun pan: slip dryer that banks on heat and time
A sun pan is an open or shallow-sided vat, typically 1 to 3 metres across and 30 to 60 centimetres deep, used to reduce the water content of slip until it reaches a workable plastic state. Slip enters at a consistency similar to heavy cream; the pan's job is to thicken it to the point where it can be cast into moulds, applied to ware, or mixed back into clay body. The process relies on both surface evaporation and, in some operations, applied heat from flues or steam pipes running beneath or alongside the pan floor.
Traditional sun pans were indeed outdoor or semi-outdoor installations that relied on direct sunlight and air circulation, hence the name. In modern facilities, sun pans are typically housed indoors and equipped with low-pressure steam heating or hot-water circulation to speed drying. The pan bottom is usually sloped toward a drain or sump, allowing settled solids to be periodically scraped and removed. Some installations have mechanical stirrers or scrapers to prevent layering and ensure even water loss across the batch.
Slip condition and settling
The critical measurement is water content, typically reduced from around 35 to 40 percent down to 24 to 28 percent by weight, depending on the type of ware being produced. Coarser particles settle toward the pan bottom while fine clay and water remain in suspension above. Operators judge readiness by feel and flow rate; properly dried slip will pour smoothly but not run off a trowel. Over-dried slip becomes lumpy and loses workability; under-dried slip will not hold shape in the mould.
Sun pans are vulnerable to contamination because they are open systems exposed to dust, debris, and bacterial growth. Larger facilities often cycle slip through the pan rather than leaving it static, moving material into casting lines or back-mixing operations on a rolling schedule. The residual sediment at the pan bottom, containing finer clays and some iron oxide from lining wear, is typically reclaimed and reprocessed rather than discarded.
In tableware and sanitaryware production, the sun pan sits between the slip-mixing area and the casting shop. Its performance directly affects casting times and the surface quality of cast ware. Smaller potteries may use a single pan; larger operations may have two or three in series or parallel, allowing continuous feed without halting the line for batch drying.