Final answer:
For coarse and resistant hair, a permanent waving solution with a higher concentration of ammonium thioglycolate is ideal. After winding the hair on rollers, an oxidizing agent like hydrogen peroxide is used to establish the new curl pattern permanently.
Step-by-step explanation:
On coarse and resistant hair, a different type of permanent waving solution is required. For such hair types, a waving solution with a stronger formulation that contains a higher concentration of the active chemical, usually ammonium thioglycolate, is appropriate. The reason behind this is that coarse and resistant hair contains more disulfide bonds which are harder to break down compared to those in normal or thin hair. These potent solutions will reduce and rupture some of the disulfide cross-links, as depicted in Figure 21.6.13, allowing the hair to be restructured into curls or waves.
After the hair has been wrapped around rollers or curlers to shape the desired curls, an oxidizing agent, like a dilute solution of hydrogen peroxide, is used to re-form the disulfide bonds in their new positions, ensuring the permanency of the wave. This permanent waving process changes the structure of hair until it is cut or grows out, as new growth will not have been treated with the waving solution.