7.6 Preliminary Tests, Foiling & Highlighting Techniques
Key Takeaways
- The predisposition or patch test is performed 24 to 48 hours before an aniline derivative colour service and checks for allergic sensitivity.
- The strand test is performed on the day of service and predicts the result, timing and condition, not allergy.
- NIC publishes the patch test as the answer to what must be performed first before applying permanent haircolour.
- Foiling isolates strands so lightener does not touch surrounding hair; slicing gives a bolder concentrated result and weaving a softer blended one.
- A metallic salt test using twenty parts hydrogen peroxide to one part ammonia detects metallic dye that would make a chemical service unsafe.
Preliminary Tests, Foiling & Highlighting Techniques
Blueprint position: Item III.E.1 requires understanding "preliminary tests (e.g., purposes, uses, applications)" with two named sub-items — (a) predisposition and (b) strand test. Item III.E.4 covers foiling. Both sit inside Hair Care Services, the 40 percent domain on both examinations.
1. The Two Named Preliminary Tests
These two are constantly confused, and the examination relies on that. They answer completely different questions.
| Predisposition (patch / skin / allergy) test | Strand test (preliminary strand) | |
|---|---|---|
| Question answered | Will this client have an allergic reaction? | What result, timing and condition will this formula give? |
| When | 24 to 48 hours before the service | On the day of the service |
| Where | Behind the ear or the inside bend of the elbow | On a small, inconspicuous strand, often at the lower crown or nape |
| What is applied | A small amount of the prepared formula | The actual mixed formula |
| Negative / positive | Negative result — no redness, itching, blistering or swelling — means proceed. Positive means do not perform the service | Not read as positive or negative; read for colour result and processing time |
| Legally required? | Required by federal labelling on aniline derivative tints; the manufacturer’s instruction governs | Best practice, not a labelling requirement |
[!IMPORTANT] NIC publishes the answer to this one. A sample theory question asks: "What should be performed FIRST before applying permanent haircolor?" — with the published key "Patch test." If an item asks what comes first, the answer is the patch test; if it asks what predicts the result, the answer is the strand test.
[!CAUTION] Aniline derivatives. Permanent oxidative tints contain aniline derivative dyes, which are the sensitisers. A prior uneventful colour service does not rule out a reaction — sensitivity develops with repeated exposure, so the patch test is repeated before each application.
2. The Other Preliminary Tests Worth Knowing
| Test | Purpose | Method |
|---|---|---|
| Metallic salt test | Detects metallic dye or compound dye from home progressive colour, which reacts violently with peroxide and can cause smoking, breakage or an unusable result | Mix 20 parts hydrogen peroxide to 1 part 28 percent ammonia; immerse about 20 strands for 30 minutes. Hair that lightens is free of metallic salts; hair that does not lighten has a coating; hair that discolours, smells strongly or boils contains lead or silver — do not proceed |
| Elasticity test | Measures cortex integrity before any chemical service | Stretch a wet strand. Healthy wet hair stretches roughly 50 percent and returns; hair that stretches and does not return, or snaps, has poor elasticity and will not withstand the service |
| Porosity test | Predicts absorption and processing speed | Slide fingers up the shaft from ends to scalp. Rough resistance means high porosity, which processes fast and grabs colour; a smooth glide means low porosity and resistance |
| Test curl (preliminary test curl) | Before a permanent wave, determines processing time and curl result | Wrap and process one or two rods, unwinding periodically to check the S-formation |
3. Foiling and Highlighting
Highlighting lightens selected strands; lowlighting darkens them. Foiling is the isolation technique that makes selective work possible: a strand is placed on a foil, product is applied, and the foil is folded so the lightener cannot touch surrounding hair.
Why foil rather than cap or freehand
| Method | Description | Use |
|---|---|---|
| Foil (off-scalp) | Strands isolated in foil; product may sit against the scalp or start away from it | Precise placement, strong lift, control over exactly which strands are treated |
| Cap | Strands pulled through a perforated cap with a hook | Even, all-over fine highlighting on shorter hair; no root regrowth control |
| Balayage / freehand | Product painted onto the surface without foil | Soft, diffused, sun-lightened effect |
[!NOTE] On-scalp versus off-scalp lightener. Manufacturers classify lighteners for on-scalp or off-scalp use, and the strongest powder lighteners are off-scalp only. A foil does not convert an off-scalp product into an on-scalp one — the classification is about the product, not the wrapping.
The two foiling patterns
SLICING WEAVING
------- -------
A straight, thin horizontal A tail comb weaves in and out of
section is lifted whole onto the section, lifting alternate
the foil. strands onto the foil and leaving
the rest behind.
RESULT: bolder, more solid, RESULT: softer, blended, more
higher contrast, chunkier. natural, lower contrast.
Placement patterns
| Pattern | Effect |
|---|---|
| Full head | Highlights throughout, section by section from nape to front |
| Half head / top and sides | Lightens only the visible surface; economical and common for men |
| Face frame | A few foils around the hairline to brighten the face |
| Teasylights / babylights | Very fine weaves for a soft, low-contrast result |
Procedure and safety
- Complete consultation, patch test 24 to 48 hours earlier, and a strand test on the day
- Section the head cleanly; work from the nape upward
- Weave or slice the section, place the foil close to the scalp, and apply lightener from about a quarter inch off the scalp outward unless using an on-scalp product
- Fold the foil in halves or thirds and seal the ends so product cannot leak
- Check the first foils placed first — they have processed longest
- Process by visual check, not by clock alone; lift is judged by the stage of decolourisation, not by elapsed minutes
- Rinse each foil thoroughly, then shampoo with an acid-balanced product and apply an acidic conditioner to close the cuticle
- Tone if required
[!CAUTION] The three faults that produce complaints. Leakage — over-saturated foils bleeding onto surrounding hair, producing bleed marks. Banding — overlapping lightener onto previously lightened hair, causing a visible line and breakage at the overlap. Uneven lift — irregular section thickness or inconsistent product loading. All three are prevented at placement, not at rinsing.
Hydrogen peroxide and lightener are covered by A.A.C. R4-10-112(L): products must be stored in clean, labeled, non-corroded containers; poisonous substances distinctly marked; a portion removed so as not to contaminate the remainder; and once dispensed, a product is not returned to the original container. Wear gloves — R4-10-112(H)(3) requires clean, fluid-proof, single-use gloves where any discharge is present or likely.
What must be performed first before applying a permanent aniline derivative haircolour?
A metallic salt test is performed and the sample discolours, gives off a strong odour and appears to boil. What does this indicate?
What is the difference in result between slicing and weaving when foiling?
When checking the processing of a full head of foils, which foils should be checked first?