Hair Coloring and Chemical Services
Colour and chemical questions reward precision: levels, developer strength, mixing ratio, patch testing and the chemistry of bonds.
Colour rules
- Level system 1 (black) to 10 (lightest blonde); natural level plus target level shows how much lift is needed.
- Developer: 10 vol (3%) deposits or tones; 20 vol (6%) covers grey and lifts 1-2 levels; 30 vol (9%) lifts 2-3 levels; 40 vol (12%) gives maximum lift but is not used on the scalp.
- Mixing is usually 1:1 for tint; high-lift blondes use 1:2. Follow the manufacturer, because ratios are not interchangeable.
- Patch test 48 hours before every colour service; strand test before lightening, perming or relaxing.
- Colour wheel: opposites neutralise, so blue cancels orange, violet cancels yellow and green cancels red.
- Virgin application: mid-lengths and ends first, roots last because scalp heat speeds processing; retouch: roots only, then pull through for the last 5-10 minutes.
Chemical services
Perms use ammonium thioglycolate to break disulfide bonds, then a neutraliser such as hydrogen peroxide or sodium bromate rebuilds them in the new shape. Relaxers use sodium hydroxide at very high pH; never apply to an irritated scalp and never overlap previously relaxed hair.
Worked example
A client with 40% grey wants a level 5 brown. Reasoning: grey hair lacks pigment, so you need a shade with good grey coverage and 20 vol, not 10 vol. Mix 1:1, apply to the grey-resistant hairline first within the development time, and strand test because the client's history is unknown.
Traps
Using 40 vol on the scalp; skipping the patch test; overlapping relaxers; neutralising a perm with conditioner instead of neutraliser.