The origin of "full" is "fullian" in the Anglo-Saxon language, meaning to whiten.

The term "fuller's soap" can be found in the Old Testament of the Bible and the Book of Mormon. Jesus' arrival on Earth is described as being “like a refiner’s fire, and like fuller’s soap.” Jesus, like the soap used by the launderers of antiquity to clean and whiten clothes, was coming to purify people and cleanse them of sin.

An Ancient Technique

According to Easton's Bible Dictionary, fulling is the ancient art of pressing or scouring cloth in a mill. Fullers also used their feet to stomp out garments. The online dictionary of the Church of Jesus Christ of Latter-day Saints explains the soap that fullers used was made from salts mixed with oil and one of two other ingredients: carbonate of soda or borax.