Final answer:
Coarse, resistant hair with a strong compact cuticle requires an alkaline chemical solution to alter its shape, such as calcium thioglycolate. This strong alkaline solution breaks disulfide bonds in keratin, allowing the hair's structure to be reshaped.
Step-by-step explanation:
In the restricting process, coarse, resistant hair with a strong compact cuticle requires a chemical solution that is alkaline. Hair consists of keratin, a protein that has strong disulfide bonds. These bonds give hair its structure and strength. To alter the hair's shape through a chemical relaxing process, a solution must break these disulfide bonds. Alkaline solutions typically contain thioglycolate, a reducing agent that effectively breaks the disulfide bonds in keratin. For example, calcium thioglycolate is used in hair removal products; it breaks down hair's keratin structure, making it easy to remove.
The alkalinity of such chemical solutions is measured by their pH level, where a pH of around 12 is maintained by adding calcium hydroxide or strontium hydroxide, allowing the thioglycolate to work efficiently. In perming or relaxing treatments as well, a highly alkaline solution is used to break the bonds before the hair is reshaped. Subsequently, an oxidizing agent is used to neutralize the reaction and reform the disulfide bonds in their new form. This reformation maintains the hair's new structure until it grows out.