The mid 1800s saw a shift in the materials used to make paper. Many mills, particularly in Scotland, began to use esparto grass as a more economic alternative to rags. Esparto is a tough grass that grows wild in North Africa and Spain. It has a short fibre length which produces a paper of bulk that is quite popular in the manufacture of writing and book paper
Esparto was fed into a large cylinder to be boiled. Caustic soda is added and the rags are boiled. After boiling, only the cellulose, which is the fibrous material that the papermaker wants, remains. The next step is to rinse and bleach the fibres in the potcher.
The potcher is an oval bath that is used to circulate the boiled fibres. The fibres are mixed with water and the caustic soda is rinsed away. After a few hours the water is drained and bleach is added to whiten the fibres.