Open-pan salt making is a method of salt production wherein salt is extracted from brine using open pans.
Virtually all European domestic salt is obtained by solution-mining of underground salt formations, although some is still obtained by the solar evaporation of sea water.
Types of Open-Pan Salt Production
Salt is made in two ways traditionally. Rock salt is mined from the ground. The other type known as white salt is made by the evaporation of brine. Brine is obtained in several ways. Wild brine streams, occurring from the natural solution of rock salt by ground water, can come to the surface as natural brine springs or can be pumped up to the surface at well, shafts or boreholes. Artificial brine is obtained through solution mining of rock salt with fresh water and is known as ‘controlled brine pumping’. A Bastard Brine used to be made by allowing fresh water to run through abandoned rock salt mines. A Salt-on-Salt process strengthens brine by dissolving rock salt, and/ or, crystal salt in weak brine or sea water prior to evaporation. Solar Evaporation uses the sun to strengthen and evaporate sea water trapped on the sea-shore to make sea salt crystals, or to strengthen and evaporate brine sourced from natural springs where it is made into white salt crystals.
This led to three types of salt production all of which used a variation of the open-pan salt method:
Coastal salt production: The process involved solar evaporation of seawater, followed by artificial evaporation of salt using the open-pan technique in structures known as ‘salterns’.
Inland salt production: The process used brine from natural brine streams flowing over buried salt deposits that were pumped up from the ground and evaporated using the open-pan technique.
Salt Refining.: This was a large-scale salt industry developed in coastal locations and based on a combination of inland salt mining and coastal salt production. Referred to as salt refining or salt-on-salt, the process combined weak brine from seawater with mined rock salt, and evaporated the brine into a white salt.
Inland Open-Pan Salt Production
Open-pan salt production was confined to a few locations where geological conditions preserved layers of salt beneath the ground. Only five complexes of inland open-pan salt works now survive in the world: Lion Salt Works, Cheshire, United Kingdom; Royal Saltworks at Arc-et-Senans, Salins-les-Bains, France; Saline Luisenhall, Göttingen, Germany;, the Salinas da Fonte da Bica, Rio Maior, Portugal; and the Colorado Salt Works, USA. The two French saltworks at Salins-les-Bains and Arc-et-Senans became a UNESCO World Heritage Site in 1982.
The earliest examples of pans used in the solution mining of salt date back to ancient times when the pans were made of ceramics known as briquetage and Cheshire VCP (Very Coarse Pottery), a coarse low-fired pottery. In Britain, these materials began to be identified from the early 1980s in the Marches (Herefordshire, Worcestershire, Shropshire and Wales) and later in Northern England
The Romans introduced small (3 ft square) pans made from lead using wood as a fuel. In Britain they established towns for salt production at Droitwich in Worcestershire, and Nantwich, Middlewich and Northwich in Cheshire. In the early Middle Ages these developed into the 'wich' towns of Cheshire. Small 'wich' houses containing several lead pans to evaporate the brine into salt, clustered around brine springs within each of the towns. The open-pan process continued largely unchanged throughout the medieval period. A 17th-century German wood-cut by Georgius Agricola shows the process in detail. Excavated evidence has uncovered wooden rakes to draw salt crystals to the side of the pan, and conical wicker baskets (barrows) in which the wet salt was drained and dried.
By the 17th century, the pans started to be made from iron, firstly in pans by . William Brownrigg writing in 1748, in his ‘Book of Common Salt’, shows a wood-cut of one of these salt-making pans. The change to iron (from lead) coincided with a change from wood to coal for the purpose of heating the brine. Gradually, the pans increased in size. For example, Christoph Chrysel writing in 1773, in his ‘Remarkable and very useful Information about the present Salt Works and Salt pans in England’, noted that salt pans were wide and long and deep. Brine would be pumped into the pans, and concentrated by the heat of the fire burning underneath. As crystals of salt formed these would be raked out and more brine added.