Chemical Services: Coloring, Lightening, Permanent Waves, and Relaxers
Chemistry you must be able to name
Developer strength is expressed in volumes and in percentage peroxide: 10 volume = 3%, 20 volume = 6%, 30 volume = 9%, 40 volume = 12%. Volume alone does not set the result - on-the-scalp lighteners, off-the-scalp lighteners, and permanent color all behave differently at the same volume. Lightening passes through the contributing pigment stages: red, red-orange, orange, gold, yellow, pale yellow. Knowing the stage tells you what toner is needed.
Safety sequence for every chemical service
Patch test 24 to 48 hours before any color or lightener service, strand test to predict timing and outcome, and read the client's history: henna, metallic salts, previously relaxed hair, and over-lightened hair are all contraindications or require reformulation. Never apply lightener to hair that has been treated with metallic salts, and never overlap relaxer onto previously relaxed hair beyond the new growth.
Waves and relaxers
Permanent waving uses a reducing agent (ammonium thioglycolate or an acid-based glyceryl monothioglycolate) to break disulfide bonds, then a neutralizer (sodium bromate or hydrogen peroxide) to rebuild them in the new shape. Wrapping tension, rod size, and processing time all change the curl. Relaxers use sodium hydroxide (lye, high pH) or guanidine/calcium hydroxide (no-lye) to straighten; they require a base, careful timing, thorough rinsing, and a pH-restoring neutralizing shampoo. A relaxer retouch touches new growth only.
Traps
Questions blur the roles of patch test (allergy screening) and strand test (processing prediction). They also imply a higher developer volume always means more lift, or that a perm can be done safely on hair relaxed the same day.
Rule of thumb
If the hair's history is unknown or contains metallic salts, do not put lightener on it - strand test first, always.