Hair Colouring and Lightening
Domain focus
Hair Colouring and Lightening tests colour theory, formulation, safety and predictable results. Expect questions on developer strength, mixing ratios, patch and strand tests, application order and correcting unwanted tones.
Core rules
- Know the level system 1 (black) to 10 (lightest blonde); colour is chosen by level and tone.
- Neutralise opposites: yellow with violet, orange with blue, red with green.
- Developer strength controls lift: 10 vol (3%) deposits, 20 vol (6%) deposits with slight lift, 30 vol (9%) lifts, 40 vol (12%) lifts and is harsh on the scalp.
- Respect the manufacturer's mixing ratio; do not add extra developer to speed up processing.
- Patch-test 48 hours before every colour service and record the result; strand-test before lightening or correction.
- Protect the skin with barrier cream, wear gloves, ventilate the area and never mix peroxide in a metal bowl.
- Virgin application: mid-lengths and ends first, then root, because scalp heat accelerates development. Retouch: root only, then refresh ends at the end of the timing.
- Lightening passes through red, orange, yellow and pale yellow; do not lift beyond the hair's tolerance. Tone after lightening, and rinse thoroughly.
Worked example
A client with 50% grey hair wants a level 6 brown. Reasoning: choose a level 6 with a natural or grey-coverage base, mix at the stated ratio with 20 vol, apply to the root first, then pull through, and time from application. A fashion shade alone will not cover grey reliably.
Traps
Overlapping bleach on previously lightened hair; skipping the patch test; leaving toner on too long; using a metal bowl with peroxide.