Chemical Hair Services (Coloring, Permanent Waving, Relaxing)
Chemistry you must own
Chemical services depend on pH, oxidation, reduction, and the hair's condition. Permanent color uses an aniline derivative mixed with hydrogen peroxide developer: 10 volume is about 3%, 20 volume about 6%, 30 volume about 9%, and 40 volume about 12%. Higher volume means more lift and more damage. Color does not lift color; a darker tint cannot lighten previously colored hair. Test porosity and elasticity, and always do a patch test 24 to 48 hours before an aniline-derivative color and a strand test for timing.
Waves and relaxers
A permanent wave breaks disulfide bonds with an alkaline reducing agent (often ammonium thioglycolate, pH around 9.0 to 9.6), reshapes hair on rods, then rebuilds bonds with a neutralizer (pH about 4.5 to 5.5). Relaxers use a strongly alkaline cream (pH around 12 to 14) to straighten; the scalp is protected, product is applied to new growth only, and a neutralizing shampoo restores pH. Never perm hair that has been relaxed with a lye relaxer without professional assessment; do not relax over a fresh bleach or an irritated scalp.
Traps
Common errors: using 40 volume on the scalp for simple gray coverage; thinking conditioner changes the color result; skipping the patch test; timing from application rather than from completion; and assuming a neutralizer is just a shampoo. Overlapping relaxer causes breakage.
Rule of thumb
Match developer to the goal and the hair's strength: 20 volume for deposit and gray coverage, 30 for moderate lift, 40 only on strong virgin hair and never as a default.
Worked example: A client with 50% gray wants a shade two levels darker. Choose the target level, mix with 20-volume developer, apply to gray-resistant hair first, and strand-test for timing.