What are pin curls placed immediately behind or below a ridge to form a wave called?

Pin curls that are placed immediately behind or below a ridge to form a wave are known as ridge curls. This technique is essential for creating structured, controlled waves in hairstyles. Ridge curls work by utilizing the natural curling action of the hair and are specifically designed to follow the shape of the ridge, enhancing the wave pattern. The placement and direction of these curls contribute to the overall form and flow of the hairstyle, making them especially useful for achieving polished looks.

In contrast, barrel curls create a different effect as they are larger and executed with larger sections of hair, producing a smooth, voluminous wave. Cascade curls refer to a technique where curls cascade downwards, providing a layered, textured appearance. Spiral curls involve wrapping the hair around a curling rod in a spiral motion, generating tight curls rather than waves. Each of these styles has its own unique application and results, but it is the ridge curl that specifically fulfills the criteria mentioned in the question.