Chemical Services (Coloring, Relaxing, and Permanent Waving)
Chemistry you must be able to explain
Hair sits at pH 4.5–5.5. The cuticle protects the cortex, where disulfide, salt, and hydrogen bonds give shape and strength. Permanent color, relaxers, and perms all work by breaking and rebuilding bonds, so every chemical service begins with a patch test (per manufacturer, usually 24–48 hours ahead), a strand test, and a scalp analysis.
Color
The level system runs 1 (black) to 10 (lightest blonde); the law of color says complementary colors neutralize (blue cancels orange, violet cancels yellow). Developer strength controls lift: 20 volume (6%) lifts about one level, 30 volume (9%) about two to three, 40 volume (12%) three to four. Temporary color coats, semipermanent deposits without lift, demi-permanent uses low-volume developer, permanent color lifts and deposits. Fill before going darker to avoid muddy or green results.
Relaxers
Lye (sodium hydroxide), no-lye (guanidine/lithium), and thio (ammonium thioglycolate) products all require a base, careful smoothing, thorough rinsing, and neutralizing shampoo. Retouch only new growth - pulling relaxer through previously relaxed hair causes overlapping and breakage.
Perms
Alkaline (ATL, pH ~9.0–9.6) versus acid (GMTG, pH ~6.9–7.2). Wrap, process, test curl, rinse completely, then neutralize, which stops processing and rebuilds disulfide bonds - the neutralizer does not "perm" the hair.
Rule of thumb
Record every formula; if you cannot strand test, you cannot promise the result.