Technical Considerations
There are two parts to a perm: the physical action of wrapping the hair, and the chemical phase. Both of these can affect the result. Important physical variables involved are what type of rod is used, how the hair is wrapped and how end papers are used. The two most common types of rods are straight and concave; each giving a different curl effect. The wrapping method is either spiral or croquinole, and various types and positionings of end papers can be used with any combination of the above. Generally, smaller rods will produce smaller, tighter curls and increase the appearance of shortening the hair.
The chemical solution used in the perming process is determined by the client's hair type and the pH of the solution. Classic alkaline perms are used for stronger, coarser hair. They work at room temperature and usually contain ammonium thioglycolate in the pH range of 9-10. Acid perms are used on more delicate or thinner hair. They require outside heat application and usually contain glycerol monothioglycolate in the pH range of 6.5-8.2.
Read more about this topic: Perm (hairstyle)
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