Soap Boiler

A soap boiler is a craftsperson who professionally makes soap by boiling fats (such as lard, butter, or oils) with lye (caustic soda or potash from wood ash) in a cauldron. 

This "boiling" was a traditional process dating back to antiquity, but in the 19th century, the craft was largely supplanted by industrial mass production in factories. 

Today, the profession is practically extinct, except among hobbyists. 

Well-known examples include soap factories along the Zaan River, such as "De Adelaar" in Wormerveer.

https://dorpenstedennederland.blogspot.com/

https://fieggentrio.blogspot.com/