In chapter 12, Atticus leaves town on a business trip, and Calpurnia decides to take Jem and Scout to First Purchase African M.E. Church for Sunday service. On Saturday night, Calpurnia makes sure the children take baths so that they will look presentable and clean on Sunday when they meet her community members for the first time. Scout mentions that Calpurnia is extremely rough when she scrubs her, and she makes her soap all over twice. Scout also mentions that Calpurnia makes her stick her head in a basin and wash with Octagon soap and castile. Octagon soap is a lye soap that was manufactured by Colgate and was popular during the 1930s. Although it was considered an all-purpose soap, many people, including Calpurnia, used it during baths. Castile soap is an olive oil-based soap that originated in Castile, Spain. It has a grease-grabbing quality that can be used throughout the kitchen but is also biodegradable and nontoxic, which is why it is safe for Calpurnia to use on Scout's hair.

The word castile is mentioned once during Harper Lee's novel To Kill a Mockingbird. It can be found in Chapter 12 as part of Scout's narration of the rough bath given to her by Calpurnia prior to their visit to the First Purchase A.M.E. Church.

She made me soap all over twice, drew fresh water in the tub for each rinse; she stuck my head in the basin and washed it with Octagon soap and castile.

Octagon soap was a popular soap in America during the 1930s. It was made by Colgate and was known for its ability as a stain and grease remover. Not only was it used for bathing, but it was also used to clean stoves and woodwork. Castile is a specific type of soap, usually made with olive oil; originating in the 16th century (probably in Belgium or France), it was probably the first type of hard bar soap, used primarily as a body wash, shampoo and conditioner.