What is the purpose of the test curl in hair treatments?

The purpose of the test curl in hair treatments, particularly in perming processes, is to evaluate how the hair reacts to the chemical solution, which directly relates to processing time and rod size. By performing a test curl, a stylist can determine the appropriate timing for the reaction to take place based on the hair's unique characteristics, such as texture and porosity. This ensures the curl sets properly, achieving the desired result without risking damage to the hair. It also helps identify the correct size of the perm rod to use, as different hair types may require different rod sizes to achieve optimal curl formation. This testing ensures that the end result is consistent and meets client expectations.