In England during the 17th century under King James I, soap makers were given 'special privileges' and the soap industry started developing more rapidly, although soaps were generally still made using caustic alkalies such as potash, leached from wood ashes and from carbonates from the ashes of plants or seaweed. The soaps made in this way were harsh and often rather unpleasant.
Soap as we know it today did not come about until the 18th century, when Nicholas Le Blanc, a Frenchman, discovered a reliable and inexpensive way of making sodium hydroxide (caustic soda), or lye as it is known to the soap maker, which forms the base with which soaps are made to this day.
Further developments in soap making were pioneered in Britain during the late 18th century with the invention of 'Transparent' soap by Andrew Pears, the son of a Cornish farmer. This refined soap was known then as it is now as Pears Transparent Soap.
Over the years and to the present day, opaque soaps have remained the favourite, mainly because transparent soaps tend to be more expensive and also don't last as long.