According to Roman legend, soap was discovered after a heavy rain fell on the slopes of Mount Sapo.

Mount Sapo means "Mount Soap" in Latin.

This hill was the site of an important sacrificial alter, and the rain water mixed with the mingled ashes and animal fat around the alter's base. As a result of the coincidence, the three key components of soap were brought together--water fat, and lye. As the mixture trickled down to the banks of the Tiber River, washer women at work there noticed their jobs easier and the wash cleaner.

Over the centuries the basics of soap making have remained generally unchanged from the Roman prescription.

How Soap is Made

All soap is made my saponification of lye, water and fat, which is a chemical process of joining acids (fats or oils) and alkali (lye, or potash & salt).

Water

The types of water generally used to make soap include rain water, spring water, or distilled water. These types of waters are considered soft and the work well because the contain few or no mineral deposits. This is important since making soap is a chemical process and these mineral deposits could possibly interact with the saponification process.

Fats & Oils

Most plant and vegetable oils can be used in making soap. Oils are used more in modern soap making because they create better quality soaps. Before oils were used, soap was made strictly from animal fats. Rendered beef tallow and pig lard were the traditional fats used. Kitchen grease was also sometimes saved and used for making soap although it was not as pleasant to use. Rendering the fats was a necessary step in the soap making process.

How to render fat- To render, fats and waste cooking grease were placed in a large kettle and an equal amount of water was added. Then the kettle was placed over the open fire outdoors. The mixture of the fats and water were boiled until all of the fats were melted. After the fats had completely melted the kettle was taken off the fire and an equal amount of water that was added the first time was then added again to the kettle. The solution was left to cool overnight. By the next day the fats had solidified and floated to the top forming a layer or clean fat. all of the impurities, being heavier than the fat remained in the water underneath the fat.

Lye (Potash)

All soap contained lye but there are different forms of it. Modern soap usually contains lye also known as caustic soda or sodium hydroxide. This creates a hard soap. Old fashioned soap was made with lye in the form of potash which was made from wood ashes. Potash alone could only create a soft gel soap but when potash was used, salt could be added at the end of the soap making process to create a hard soap. This was seldom done because the cost of salt was great and was more valuated for curing and flavoring food than making soap hard.

How to make lye- Creating the lye was the first step in soap making. Ashes would have been collected and saved from the hearths all winter. Oak wood is said to produce the best lye but any type of wood can be used because lye can be weakened or strengthened as needed by boiling it down or diluting it with water. Lye was traditionally made with the use of an ash hopper. The ash hopper is a boxy, four sided barrel that is similar to a large funnel in that it is wide at the top and gets narrower towards the bottom. The hopper is set into a simple wooden frame with four legs. The legs suspend the narrowest part of the hopper barrel over a wooden collecting bucket. Inside the barrel several small holes were drilled and a layer of straw would be placed over the holes as a filter. The barrel would be filled with ashes about four inches from the top. Spring (or soft) water would then be boiled in a kettle and slowly added to the ashes. Once the water was absorbed into the ashes, cold water was added until water began to trickle slowly from the small holes in the hopper into the collecting bucket. More ashes would then be added to the hopper, again up to within four inches from the top. More boiled water was poured over the ashes but not so the ashes were swimming. The hopper would then be left for four hours so that the lye water could trickle through the holes into the collecting barrel. After the four hours have passes, the collector barrel full of lye water would then be removed. A new collecting barrel would be placed under the hopper and some new ashes be put in the hopper. The prepared lye water would now be caustic, so gloves and protection was a must. The prepared lye solution would be poured into the hopper again. Then two to three small buckets of cold water poured slowly over the ashes. Once the water had stopped running through the holes the process was complete and a strong solution of lye had been created.