Chemical Services and Hair Color
Chemistry of colour and texture services
Understand the structure of hair and how the cuticle must open for colour or relaxer to work. Know the role of developers, hydrogen peroxide and ammonia, and how volume affects lift. Learn the difference between temporary, semi-permanent and permanent colour, and how each interacts with the hair. Understand the pH of relaxers and how they alter the hair's bonds.
Consultation and safety
Know how to perform a patch test and a strand test, and when each is required. Understand the signs of an allergic reaction and how to respond. Learn about mixing ratios, processing time, and the importance of following manufacturer instructions. Know how to assess hair condition before a chemical service and when to refuse or postpone it.
Traps to watch
Questions often confuse volume numbers with lift or with processing time. Remember that higher developer volume means more lift, not a longer processing time. Another trap is the difference between a patch test (allergy) and a strand test (result and timing). Watch for questions about overlapping colour on previously treated hair, and about relaxing previously relaxed hair. Also watch for the rule that metallic salts and some products can react badly with colour.
Rule of thumb and worked example
Rule of thumb: always patch test 24–48 hours before a colour service, and always strand test before a relaxer or a major colour change. Example: a client wants to go from dark brown to blonde. Strand test to check lift and condition, then plan a multi-step process rather than one strong application.