Hairdressing Sciences

One of a series of articles in which Mr D Dane FTTS MAE
(a clinical hair-scientist, microscopist, Fellow and Past President of The Trichological Society)
addresses scientific and practical issues associated with certain hairdressing procedures:

COLOURING - DECOLOURING the HAIR

Processes, precautions and industry-accepted procedures for the
Colouring and Decolouring of Hair.

FOREWORD:

Practising hair scientists are often clinical practitioners, not hairdressers - to be fully competent in their specialty hair scientists need to understand the science and art of the hairdresser insofar as procedures of the latter performed upon hair and hair-bearing skin might bring problems upon their clients, who might later need the trichological advice of a hair scientist concerning such matters.   This article provides insight into the hairdressing industry's expectations of a 'reasonably competent' hairdresser in the art of hair colouration in all its various forms - and should therefore be of value to any hair scientist particularly in Expert Witness work.

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Processes, Precautions and industry-accepted Procedures for the Colouring and Decolouring of hair .

1)   COLOURING HAIR :

Colouring (or 'tinting' or 'dyeing') is the name given to the physical and chemical process of colouring the whole structure through any hair shaft, artificially.   Such artificial colour may be of several different forms - permanent, semi-permanent, quasi-permanent, colour-rinse, or shampoo-colour. The physical part of the process involves separating strands or meshes of the hair and treating each in turn with active chemicals, encompassing the whole head of hair or the selected part that requires colouring, to obtain the shade of colour desired by the client and agreed upon in prior consultation with the hairdresser.

Other than rinses and shampoo-colours, hair colour products (those of para-dye type which through inherent toxicity will always need a prior patch test) are all oxidation-dyes that require activation by a developer, usually hydrogen peroxide of varying volume-strength.   After prior inspection, the precautions for skin-sensitivity or potentially existing sensitisation (by a prior patch test to the client's skin) and for the proposed product and process suitability to the hair (tests to that hair for compatibility, acceptable porosity, elasticity) need to be made.   Apart from water-rinses, shampoo-colours and 'semi-permanent' colours ( ' one bottle, tube, sachet or spray only ' type of product) hair colouring relies on the chosen colourant product being activated by free active oxygen from a chosen strength of hydrogen peroxide, separately added.   Since the chemical structure of the hair is to be acted upon, to prevent over-processing and consequent damage to hair shafts as well as the possibility of 'chemical burning' of skin it is necessary for the hairdresser to understand and be fully competent in the safe practice of accepted techniques used for creating various colour shades when putting para-dye or other active chemical colourant onto either a full head of hair (particularly if as a first-time colourant) or onto current regrowth (a root-retouch) where in both cases skin-contact is involved, to match up to pre-existing coloured mid-lengths and their ends - or onto selected strands of hair such as high-lighting or low-lighting using chemicals of higher power which must be kept away from skin contact.

The scalp should first be carefully inspected for signs of infection cuts or abrasions or any pre-existing skin condition or acknowledged sensitivity.   The whole length of all areas of hair shafts should be closely inspected for texture and tests made to reveal any incompatible chemicals or other materials that may have been used or may be coating the hair, for variations of porosity and for their elasticity both in the dry and wet state.

If there is any sign of abnormality of either the scalp or the hair, decolourants/colourants must not be used.   Though usually 'mythical' nor should such chemical application be made if there is any doubt as to possible effect of any medications chronically being taken by the client however unlikely an effect from that source might seem.   Such reservation could be a rare possibility and here the client must have received consultation and be advised to seek a GP's advice before chemical hair-treatment is performed.

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2)   DECOLOURING HAIR :

Decolouring (which includes 'bleaching' and 'high-lift tinting' ) is the name given to the physical and chemical process of lightening the natural colour pigment of hair.   The physical part of the process involves separating strands of the hair and treating each in turn with active chemicals, encompassing the whole head or the selected area that requires decolouring, to obtain the degree of colour lift or lightening desired by the client and agreed upon in prior consultation with the hairdresser.   Decolouring must not be confused with ' correction' by a 'reduction' process.

Hair decolouring products (including those of non para-dye type, eg: paste bleach) all involve oxidation processes that require activation by a developer, usually hydrogen peroxide of varying volume-strength.   After prior inspection,

full precautions for skin-sensitivity or potentially existing sensitisation by a prior patch test to the client's skin if of a

proposed paradye, and for proposed product and process suitability to the hair (tests to that hair for compatibility, acceptable porosity, elasticity) need to be made.    De-colouring relies on the chosen decolourant product being activated by free active oxygen from hydrogen peroxide.   Since the chemical structure of the hair is to be acted upon, to prevent over-processing and consequent damage to hair shafts as well as possibility of 'chemical burning' of skin it is necessary for the hairdresser to understand and be fully competent in the safe practice of accepted techniques used for creating various lighter shades when putting bleach or other active chemical decolourant onto either a full head of hair (eg: as a first-time decolourant) or onto current regrowth (a root-retouch) where in both cases skin-contact is involved to match up to pre-existing decoloured mid-lengths and their ends - or onto selected strands of hair as with high-lighting using chemicals of higher power which must be kept away from skin contact.

The scalp should first be carefully inspected for signs of infection cuts or abrasions or any pre-existing skin condition or acknowledged sensitivity.   The whole length of all areas of hair shafts should be closely inspected for texture, and tests made to reveal any incompatible chemicals or other materials that may have been used or may be coating the hair, for variations of porosity and for their elasticity both in the dry and wet state.

If there is any sign of abnormality of either the scalp or the hair, decolourants/colourants must not be used.   Though usually 'mythical' nor should such chemical application be made if there is any doubt as to possible effect of any medications chronically being taken by the client however unlikely an effect from that source might seem.   Such reservation could be a rare possibility and here the client must have received consultation and be advised to seek a GP's advice before chemical hair-treatment is performed.

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The hair may or may not possess a degree of pre-existing decolouration from 'weathering' or from earlier chemical treatment and will most likely have variable porosity down its length, even the distal ends effectively being 'bleached' to a degree.   Such hair or part of its length might require later additional colour toning with a weak form of hair dye.   In that instance the hairdresser should be wary of the usual brown shades which of necessity contain blue pigments that will fix to the yellow colouration of bleached or decoloured hair and may in particular result in unwanted greenish shades.   Normal strength hair dyes must therefore not be used as toners.   Following a bleaching or decolouring, a toner (usually an especially weakly-formulated dye of para-dye type) may after further appropriate tests for porosity elasticity and a skin-sensitivity patch test 48 hours earlier , be applied upon that decoloured hair to produce various colour effects either blending or contrasting with the client's natural colour. There can only be minimal control of development of such a toner on this already chemically decoloured hair.   Apart from adding further chemical activity it may develop colouration intensely as well as speedily.   Minute-by-minute checks must be made to prevent over-processing of hair when using any 'colour change completion technique'.   Paradye, especially dark or red shades, cannot be successfully removed by bleach and a special 'colour reducer' (stripper) technique exists for that 'correction' purpose.   But special measures are needed (with experience and qualifications to match) to be able to successfully utilise such colour reduction method.   It should never be undertaken lightly.

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SAFETY :  

Skin inflammation and the need for Tests before applying Decolouring or Colouring products:

A skin inflammation may be caused in the hair-salon by a 'thermal' burn arising from being overheated by a piece of salon equipment.   For instance: undue exposure under a heated hood-hairdryer, infra-red array, steamer, or contact with hot irons.   Sensitivity of skin/scalp tissues to either tension or heat should also always be considered.

In practice a 'chemical' burn of skin tissue is the more likely and a hairdresser must constantly guard against such an event occurring when carrying-out any form of chemical treatment, to eliminate inflammation risk.

The safety of both the skin and of the hair of the client must receive the utmost forethought and consideration.

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Hair salon chemical treatment as a cause of inflamed skin :

In hairdressing, external factors are predominant and if a skin inflammation (dermatitis or eczema) arises when using active chemicals it may be classed under two distinctly different and separate clinical patterns.

Unfortunately much confusion exists between the two:

i) Irritant contact dermatitis    

This is a direct reaction pattern and can occur with skin of normal sensitivity.   In this pattern certain chemicals are capable of causing dermatitis in everyone if applied in sufficient concentration for long enough or repeatedly.   Such chemicals are called primary irritants . Some strong primary irritants used by hairdressers may cause dermatitis after only one exposure.   Irritant dermatitis may form blisters on a background of redness and swelling. Symptoms are tingling, itching and the later development of weeping followed by a crusting scaling area of inflammation.   The reaction occurs only at the site of exposure to the chemical.   Permanent-wave lotion is an example of 'primary irritant'. Hydrogen peroxide is another.   Although it is an accepted and wise standard precaution, patch testing prior to exposure here is valueless so great care must be taken at all times to prevent skin contact with potential irritants.  

ii) Allergic contact dermatitis

This is an immunological reaction and cannot develop until the body has earlier become sensitised to a particular agent.   Allergy Sensitization , if it occurs takes a minimum of four or five days to develop and results in production of antibodies that reach the skin of the whole body. Subsequent exposure of the skin anywhere to that agent then provokes dermatitis.   Unlike irritant contact dermatitis, allergic contact dermatitis often spreads to sites away from that of exposure.   The symptoms are itching and the later development of redness, and an often severe swelling.

Para-dyes are known sensitizers.   Prior patch testing should determine an individual's state of immuno-sensitisation.

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TESTS:

A)  The SKIN :

The Skin-sensitivity or Patch Test :   Most modern hair dyes contain varying amounts of phenylenediamine and/or toluenediamine.   These are known and accepted toxins which, having once sensitised the body via skin contact it becomes possible or likely for an allergic reaction to occur on the next and any subsequent occasion of skin contact.   These dyes are known as 'para-dyes'.   When presence of para-dye is shown in either the colourant or decolourant in any product proposed for use in changing the colour of hair a skin-sensitivity test (patch test) must have been carried out 24-48 hours each and every time before any proposed application whether in the past this has proved unnecessary for the client or not and found to show no allergic or other adverse reaction (any itching or reddening) prior to work commencement.   If a para-dye tint is to be used as a de colourant, as for example 'high-lift' products, or if it is likely that any type of decoloured hair will later require toning (using a para-dye tint 'toner') it is equally essential that a Patch Test for skin sensitivity of possible allergic or other response has been carried out at least 24 to 48 hours before such colour application.   In both situations a patch test is therefore best applied at the time the client makes an appointment for the work, as also is the taking of hair-strands for ' product and process suitability' testing to reveal and quantify any incompatibility , any variation in hair shaft porosity down the lengths and any weakness of elasticity .

Instructions as to how to make a patch test are usually given with all products containing para-dyes.   This requirement must not be ignored.   When proposing to use only a toner upon existing bleached or non para-dyed hair, assurance should be sought that there has been no skin reaction to a patch test applied 24-48 hours earlier even though, when perhaps using non scalp-contact technique such as foil-wrapped processing, in principle such toner might not be put in direct contact with the scalp upon application.   In practice there is a high risk of skin contamination and reaction, even if only when washing-off that toner.  

B) The HAIR:

Apart from a 'skin-sensitivity test' (patch test) the National Occupational Standards for hairdressing define three specific tests to be made upon the hair.   They are for a) incompatibility , b) porosity , and c) elasticity .   These three tests are done before commitment to 'Colour Change' either 'in situ' on the client's hair or on a current sample cut from that hair, to measure 'proposed product and processing suitability' for the hair in its current state .  

Test a) is undertaken to show up incompatibility of the hair with any materials with which that hair is proposed to be used, to allow the operator not only to correctly choose the required type and strength of product but to accurately gauge a safe processing-time and lowest temperature needed for a satisfactory result, with neither hair nor scalp damage arising.   It requires the full length of several strands to be separated out from near the nape of the neck, isolated from the bulk of hair.   Small 'test cuttings' of that separated hair should be tested by immersing them in 20-volume hydrogen peroxide made alkaline by the addition of a few drops of ammonium hydroxide solution ('household ammonia') to allow the release of oxygen.   If after a few minutes of development on the 'cuttings' any discolouration or heating occurs (a likely indication of presence of metallic salts ) the decolourant/colourant process should not be proceeded-with.   Although professionally trained hairdressers are unlikely to be able to obtain metallic salt dyes from their wholesaler and they are not nowadays used in the salon, they may be encountered having been purchased retail and used by their client upon the hair . Such dyes are still to be found in the wide cosmetic retail marketplace and hairdressers need to be assured that they have not been used by their client on any part of existing hair length and that a chemical reaction between a suspect or possible 'salt' and their professional product will not be a possibility.   Hair length means 'past passage of time' and a hairdresser cannot know with certainty what that hair length has been subjected-to.   If all is well with the test cuttings, the proposed decolourant/colourant (whether bleach or dye) may now be applied to the separated test-strands and processed without added heat or according to the product manufacturer's instructions , combing and smoothing with the back of a wide-toothed comb but isolated away from other hair.    Alternatively a mesh or meshes may be cut off from nearest scalp level and laid out on an inert surface.   The proposed decolourant/colourant is applied to the meshes' entire length and processed without added heat or according to the product manufacturer's instructions , combing and smoothing with the back of a wide-toothed comb.   The active chemicals or products intended to be later used on the whole head of hair should for this test only include and cover the regrowth and overlap onto any previously-treated length of hair shaft to ensure compatibility with the whole hair whatever treatment that existing hair length had previously received, and should be processed for this test for at least the manufacturer's recommended normal processing time and at ambient (room) temperature ( without added heat - unless manufacturer-recommended).   The results should be checked throughout the test-processing at 3-5 minute intervals.   Any change in colour heat or tensile strength during that test-processing should be noted and recorded. The minimum time required to give the desired colour-lift (if decolouring or bleaching) or colouration (if colouring, tinting, dyeing) should also be recorded.   The test chemicals should then be washed off and the strands checked again for Test b) any sign of untoward hair shaft porosity or damage, and Test c) the hair's elasticity or tensile strength down its entire length as a result of this sample proposed treatment.   Such tests, which take time are best done when the client requests the appointment - before the appointed date. Uncertainty must always exist over the possibility of other chemical treatments (or even cosmetic hair products) that may have affected the hair since the last tried-and-trusted treatment. A client's body-chemistry could also possibly have changed over time.   For safety and success therefore the above three tests should be made before each and every application of active-based chemical decolourant or colourant (whether hair dye or bleach) in order to ascertain the current wisdom of whether or not to safely proceed as proposed.

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Industry accepted 'Performance Criteria':  

dictates that records of the outcomes of all the above tests are accurately written onto the client's Record Card for each occasion of a treatment, and that after the chosen treatment has been carried out a record of all products used, strength of activator, type of temperature whether ambient or machine-added, total development time from commencement of application, and any other salient points be likewise accurately written onto the client's Record Card.

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An explanatory note on:

HYDROGEN PEROXIDE - used in the salon as 'activator' of Decolouring and Colouring products.

The chemical structure of this compound is H 2 O 2 (or H-O -O- H).   It is therefore loosely related to water but has a controlled amount of active oxygen dissolved within it which, when released, will oxidise the product with which it is mixed and also oxidise or de-construct the material on which that mixture is deposited. In hairdressing that material is the hard keratin of hair - and if in contact the soft keratin of skin - to a given degree according to its 'strength' of dissolved oxygen. That strength is measured in 'volumes' of available active oxygen per unit volume.

It is a dangerous liquid and must always be used with care.    The strength is often given as a 'percentage' figure.

one 'quantity' of 3% hydrogen peroxide contains 10 times its volume of oxygen to become free and active.

one 'quantity' of 6% hydrogen peroxide contains 20 times its volume of oxygen to become free and active.

one 'quantity' of 9% hydrogen peroxide contains 30 times its volume of oxygen to become free and active.

one 'quantity' of 12% hydrogen peroxide contains 40 times its volume of oxygen to become free and active.

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60volume ( 18% ) and 100volume ( 30% ) hydrogen peroxides exist, but have no place in a hairdressing salon.

40 volume (12%) is the highest strength that may be used as a salon-use activator but then only if for non scalp-contact use mixed with a product such as highlift cream tint (or bleach if manufacturer allows, for off-scalp use only) that will reduce its strength from harmful direct activity upon scalp (or hair) and only when used at room temperature .   Otherwise 30 volume (9%) is the highest strength of peroxide that may be safely used in a product liable to contact the skin even at room temperature.

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PROCEDURES for Decolouring and Colouring:

Pre-Application - Whether of standard or highlift dye or of bleach, those tests already outlined for incompatibility, porosity and elasticity must have been made, note taken of the client's skin condition and sensitivity, and records made.   If use of para-dye of any strength or shade is contemplated a patch test must have been carried out 24 to 48 hours before the proposed treatment and be seen to have had no adverse reaction.

It is common practice that application of decolourant/colourant is carried out as follows:

The hair should be combed well free of tangles. The scalp should not have been shampooed for 2 days before proposed treatment as, if done within the two days this will have removed the natural protective mantle of oils rendering both scalp and hair more sensitive to the proposed chemical activity.

Method : - for full virgin-head or full virgin hair-shaft length - the head of hair is parted into four quarter sections and each in turn is worked upon upwards from the nape .   Decolourant/colourant is applied by brush or applicator-nozzle as quickly as possible via horizontal or sometimes vertical parted sections - commencing 2cm (at least ½´´) from the scalp.   If the pre-treatment tests showed that the ends of the hair had 'lifted' or developed quickly

(indicating a greater porosity here) the chemicals should be applied to the mid-lengths first, never to the 2cm nearest the scalp , also leaving the hair ends free of decolourant/colourant.   It must be remembered that normal body-heat of the scalp accelerates the strength and speed of chemical development near scalp level, as well as rendering the scalp increasingly sensitive to the chemicals.   Application to then complete work to the hairshaft ' ends' - and at the area known as 'roots' two centimetres nearest scalp down to actual scalp contact - should therefore be done last.

- for a full root-retouch decolouring/colouring application - the procedure is the same except that the active chemicals should be applied only to the regrowth, nearest upon the scalp.   If the boundary of this regrowth is greater than 2cm from the scalp the decolourant/colourant should first be applied section-by-section at the 1cm-2cm from scalp point but not overlapping onto any pre-existing treated length until all sections have had application - before then re-applying the chemicals in scalp contact over the whole regrowth.   Only then, when development has evenly commenced may the decolourant/colourant be applied as a toner-application down previously treated lengths, first to mid-lengths of each section and then only finally to the distal ends of these previously chemically-treated lengths.   Care must always be taken preferably to keep the chemicals from overlapping onto any previously lightened or coloured hair lengths other than in this instance.   Destructive hair damage can easily be a likely consequence.

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Highlights, Lowlights, Strands, Streaking, Weaving, Flashes, Bands, are names given to separate strands of bleached (or nowadays more usually 'high-lift tinted') lightened hair.   The technique required to produce these highlights or lowlights is different to that of general root-retouch or full-head decolouring/colouring but the precautions to be taken are the same.   The applied chemicals should never be occluded under a plastic bag or have added-heat applied.

If the head of hair is short , selected strands may be pulled through holes in a protective rubber mesh-cap for the active decolourant to be applied safely.   For shoulder-length or longer hair foil or special mesh-wraps must be used to totally encase the strand with its active decolourant without strain or pain upon the scalp or hair.

Due to the strength of the peroxide activator when carrying out lowlights or highlights there must not be any skin contact with the decolourant , be it bleach or tint, nor must such contact become likely during the development or processing period; eg: through carelessness or occlusion or use of added heat.   Only if that consideration of safety has been assured may the appropriate stronger chemicals be employed.  

Slices, Tipping, Comb-through Lightening, Frosting, Brightening, Painting and Blending are terms used to describe the effects of using a permanent hair-dye or straight bleach as lightener on a section of hairs or parts of hairshafts selected from a head of hair .   They are achieved without scalp contact in similar fashion to 'highlights'.

Method 1 :   If the hair is short (above shoulder-length) strands of hair may be pulled through holes that have been strategically placed in a close-fitting special silicon or rubber mesh-cap, using a crochet-hook.   The bleach or hair-dye is then applied with either a brush or applicator-nozzle as quickly as possible. With this method there is no guarantee of measure of strand thickness or of accurate strand positioning and this can create an uneven colour-balance.   A mesh-cap should never be used for hair longer than shoulder-length or when the head of hair has a strong natural wave or is particularly dense.   It is usually impossible to remove a mesh-cap from long or curly hair without hair damage.   The mesh-cap must keep the decolourant/colourant from seepage or running through onto the main head of hair underneath and especially from contacting the scalp, forehead, ears, or other tissues. The chemicals must not be allowed to dry out but they should never be enclosed under a close cover (plastic bag) that will most likely prove gas-tight and cause seepage onto the skin tissues by 'blow-back' of active oxygen, causing both chemical burns and a likely over-processing of the hair.   The client's head may be covered loosely by a porous paper or cotton towel but is

usually more wisely left uncovered.   Processing is best and safest done at room temperature. The client's comfort and safety must be monitored continuously.   Only if specified by the product-manufacturer should chemical development be speeded-up by placing the head within an infrared accelerator or steamer.   In such situation on no account should a head with mesh-cap ever be covered under a plastic bag.    A heated hairdryer should never be used.

Method 2 :   If the hair is below -shoulder length small strands may be wrapped in aluminium foil or commercially prepared streaking-packets. These retain heat produced by the oxidising activity of the decolourant/colourant as well as from the head.   The decolourant or bleach should have been applied more sparingly at the 'root' end of the strand to accommodate any later swelling of the packet.   Such swelling is possible even at room temperature.   The packets should be firmly enclosed to prevent chemicals seeping out onto other parts of the head of hair or onto the client's scalp.   Cotton-wool strip may be loosely placed under and around each foil parcel for support and scalp safety.   A steamer, hairdryer or any other form of added heat must never be used since the enclosed decolourant/colourant will liquefy, active gases will expand rapidly and will most likely cause the active chemical contents to burst through the foil contaminating both the head of hair and the skin, with great possibility of causing chemical burns and over-processing of the hair.   Foil parcels or streaking-packets must never be covered or heated.

The "weaving" technique is a useful variant of this method.   The hair is first divided and pinned-up into clean sections starting from the front.   Commencing with a nape section, a wide mesh of hair is finely woven-through with a tail-comb taking say 10 fine strands every time.   A strip of foil is then placed underneath each isolated mesh, the decolourant or bleach is brushed on, being applied more sparingly at the 'root' end of the mesh to accommodate any later swelling of the packet which is possible even at low room temperature.   The foil is then carefully folded and secured to make a neat flat parcel.   Working from the nape upwards this weaving is continued until there are the required number of parcels depending upon the desired highlighting effect.   It would take a reasonably competent practitioner say 45 minutes to weave and wrap a head of hair into such parcels.   For reasons already given, the parcels must never be covered under a plastic bag or other occlusion and added heat never be used.

With either individual strands or woven meshes and whether in foil, streaking packets, or resting on layers of foil, processing-time guidelines given by product manufacturers are usually a maximum of 50 minutes.   It can therefore be seen that the first parcels packets or layers should be removed as soon as the last ones are completed - if not sooner! - and it is important that the chemicals on the hair of those first unwrapped ones should immediately then be well diluted with water-soaked cotton swab to reduce further chemical activity on that first-treated hair.

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FOR ALL TECHNIQUES :

PROCESSING of Decolourants/Colourants :

a)    At all times the Manufacturer's Instructions must be followed, but with respect to the above-given knowledge.

b)   Development time starts from the moment the first hairs of section, strand,   parcel or layer have the chemicals applied - not when the treatment application       has been completed.

c)   When application is complete the chemicals should be left to develop at room temperature uncovered or only lightly-so. Frequent checks on selected strands for       colour development must then be made, and scalp condition observed. [see ' Strand Test ' under later ' Review and Considerations ' at paragraph 8 of this       paper]     

d)   Frequent cautionary checks must be taken regarding temperature, timing, skin-comfort and/or contamination.

e)   Diluted decolourant/colourant may be combed gently through the hair near completion of development, to even-out the colouration upon varying porosity of hair       lengths.

f)    If the decolourant is specifically a bleach, added heat must never be used (ie: that from a heated-dryer,steamer, infra-red array or any other form of       accelerator) unless this has approval of the manufacturer of the product.   Nor should bleach chemicals ever be processed under occlusion or any form of cover.

g)   With a para-dye decolourant (eg: high-lift tint) the head must not be covered unless recommended by the product manufacturer, and never when a mesh-cap or       foil packets are being used.

h)   If for some special reason heat has to be used to develop an applied active-chemical, close consideration should have been given to the sensitivity of the       client's scalp and surrounding tissues as well as to any pre-existing chemically treated lengths.

i)   As soon as an even and satisfactory degree of colour depth or lift has been achieved the decolourant/colourant should be rinsed from the hair and all chemical      traces thoroughly shampooed from the scalp.

j)   After removal of the decolourant or colourant, rinses containing the following substances may be used:

   i.   an Anti-oxidant .   This stops any further bleaching lightening or colouring action.

  ii.   an Acidic product - for neutralising any alkali left in the hair and to close the cuticle scales to make the hair smoother, adding lustre and 'comb-ability'.

  iii. a hair Conditioner (usually of cationic or 'electrically positive-charged' form).   NOTE: - all chemical processing necessarily weakens hair to some extent and it       is for the hairdresser to have minimised that 'acceptable damage' as much as possible.   Such hair takes up more cationic conditioner than untreated or virgin       hair due to electrostatic attraction of these 'conditioner compounds' to the hair.   A cationic conditioner also helps smooth the hair cuticle, improving strength,       lustre and manageability.

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NB: If it is proposed to lighten a dark shade of virgin hair, but especially of previously dark or red artificially coloured hair to a very much lighter shade it should be realised that this is a drastic measure and that a probable high degree of permanent and destructive hair damage will be a likely consequence.
Dye-colour correction is a highly technical expertise requiring proper 'qualification' [such as NVQ hairdressing at Level 3] and is a serious matter.

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Review and Considerations :

1. All prior tests must always be made for incompatibility, porosity and elasticity, and therefore of hair-suitability to the proposed chemicals and the proposed process.

2. A patch test for skin sensitivity must have been carried out some days beforehand if there is to be a para-dye component in any product to be used, to warn of possible acquired allergic sensitivity - before proposed work.

3. If attempting to produce light shades on virgin hair, decolouring may only be undertaken over several separate treatments - using low volume strengths of peroxide in the product-mixes, never one high-strength treatment.

4. Generally the less porous parts of a client's hair shafts are treated first.   The chemicals should be applied quickly and evenly.   It is important not to overlap onto previously decoloured/coloured more porous parts.  

5. Tint and paste bleach requires smaller sections compared to the less commonly used liquid or oil bleach.   But whatever type of decolourant/colourant is used a quick application-time is essential.

6. For strands (highlights, lowlights) - foil or commercially prepared ' wraps ' must be used on any head of hair that is dense, long or very wavy.   A mesh-cap may only be used on hair that is less than shoulder-length.

7. Hair damage however slight is very likely to lead to hair breakage later.

8. The National Occupational Standards (NVQ in Hairdressing) consider the phrase 'strand test' only in the context of checking of colour or bleach during the development process seen upon a selected strand to gauge if the hair has reached the desired colour.   Following such development check or strand test, the colour or bleach will either have developed to the target colour - or the colour or bleach may require further development.   Such check or test must not be confused with the preliminarily required Patch test or Sensitivity, Hair Suitability and other pre-treatment tests.

9. When lightening previously darker or red dyed hair a ' colour reduction' process must first be undertaken, not the application of any peroxide-activated product such as hairdye or bleach.   Such work will require more advanced knowledge from the hairdresser (at NVQ Level 3 qualification)   - and if it had been a dark or red dye, to achieve safe acceptable results the work may have to be undertaken through several sittings, never by multisession processings.

10. With all colouring/decolouring work, multiple processings upon the same hair shafts must never be undertaken at the same sitting or 'over-processing' and hair breakage will most likely result.

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OVER-PROCESSING :   - overprocessed hair is that in which cuticle and cortex have been caused to lose structure.

- may be caused by any single factor or combination of the following:  

i) too high a strength of developer or activator (hydrogen peroxide).   

ii) processing for too long (total figure for this must include application-time from its commencement).

iii) processing at too high a temperature.  

iv) processing dye or bleach on top of a previous application, or allowing that hair to become overlapped.

v) combing full-strength decolourant/colourant through already treated or pre-existing porous hair. Any overlap on either of these types of hair (other than of specifically-diluted mixture as per manufacturer's instructions) could easily result in breakage.

Over-decolouring/colouring (over-processing) results in the hair becoming very brittle when dry, spongily porous, and often unevenly-coloured. Over-processed hair is likely to be very stretchy like chewing gum when wet, and any resultant shape of setting will soon be lost. The structure is so weakened that the hair will break even by bending and under very little tension. The breakage may be partial across many hairshafts and invisible to the eye. This breakage may therefore not be noticeable at the time of treatment but is often realised by the client only later in normal daily wear, washing or grooming once the hair has properly dried.

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WARNING :

If, with any technique during the treatment the client makes mention of scalp 'burning' or even only of 'tingling' 'irritation' or 'itching' all chemicals should immediately be washed thoroughly from both the hair and the scalp, and the treatment discontinued.   

This is an imperative duty of care.

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© D Dane FTTS MAE (refer to the author)
 
Hair-sciences & Hair-specialisms - The Trichological Society

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