Final answer:
Pin curls placed immediately behind or below a ridge to form a wave are called Ridge curls. Such curls, which contribute to temporary waves, involve water molecules changing the hydrogen bonds in keratin strands, while permanent waves affect disulfide bonds for a lasting shape.
Step-by-step explanation:
Pin curls placed immediately behind or below a ridge to form a wave are called Ridge curls. This technique is used in hairstyling to create waves and volume by the strategic placement of pin curls. When creating a temporary wave, water molecules penetrate the keratin strands in the hair, disrupting some of the hydrogen bonds that help maintain the hair's shape. As the hair dries, these bonds reform, allowing the strands to hold a new shape temporarily.
Permanent waves, on the other hand, involve the disruption and reformation of disulfide bonds within the hair structure, leading to a more lasting change in the hair's shape. Both temporary and permanent waving techniques rely on altering the hair's chemistry to achieve the desired curl pattern.