Production of Salt
On an industrial scale, salt is produced in one of two principal ways: the evaporation of salt water (brine) or by mining. Evaporation can either be solar evaporation or using some heating device.
Solar evaporation of seawater
In the correct climate (one for which the ratio of evaporation to rainfall is suitably high) it is possible to use solar evaporation of sea water to produce salt. Brine is evaporated in a linked set of ponds until the solution is sufficiently concentrated by the final pond so that the salt crystallizes on the pond's floor.
Open pan production from brine
One of the traditional methods of salt production in more temperate climates is using open pans. In open-pan production, salt brine is heated in large, shallow open pans. The earliest examples of this, date back to prehistoric times and the pans were made of either a type of ceramic called briquetage, or lead. Later examples were made from iron. This change coincided with a change from wood to coal for the purpose of heating the brine. 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.
Closed pan production under vacuum
The open pan salt works has effectively been replaced with a closed pan system where the brine solution is evaporated under a partial vacuum.
In the second half of the 19th century, industrial mining and new drilling techniques made the discovery of more and deeper deposits possible, increasing mine salt's share of the market. Although mining salt was generally more expensive than extracting it from brine via solar evaporation of seawater, the introduction of this new source reduced the price of salt due to a reduction of monopolization. Extraction of salt from brine is still heavily used for salt used in cooking.