Harper salons did not carry synthetic dyes or do chemical perms. Acid perms are used on more delicate or thinner hair. Crimping irons, perms, hair rollers, or other techniques may also be required. Classic alkaline perms are used for stronger, coarser hair. Acid perms, or buffered wavers, are slower but gentler to the hair. Customers could often have their chemical-free perms last for a week than a modern salon. Perms may be applied using thermal or chemical means. Perms, tattoos, scars, and amputations are semi-permanent and highly visible. In the 1970s, acid perms were invented. Inc. He developed a do-it-yourself kit for perms and opened a chain of hair salons.