FR2657781A1 - Process for lightening or erasing the colour of dyed hair and compositions employed - Google Patents

Abstract

The invention relates to a process for erasing or lightening the coloration of dyed hair, consisting in applying to the dyed hair, in a first stage, an acid solution of potassium permanganate and, in a second stage, a solution of a reducing agent chosen from sodium bisulphite, sodium hydrosulphite, cysteine and oxalic, thioglycolic, citric and ascorbic acids.

Description

Process for lightening or erasing the color of dyed hair and compositions used.

 The present invention relates to a new process for lightening or erasing the coloring of dyed hair, as well as to the compositions used.

 It is well known to dye the hair in various shades and colors, using precursors of oxidation dyes or even indole dyes, such as 5,6-dihydroxyindole or its derivatives, which may be revealed by an oxidizing system or even by a direct dye using so-called "direct" dyes.

 We wish, in the field of hair coloring, sometimes to erase the artificial color which has been given to them or to lighten it. Generally, bleaching methods are used for this purpose, which are also used to bleach hair and destroy the natural color of the hair.

 These processes are generally based on the use of oxidizing mixtures, such as hydrogen peroxide, persalts, percarbonates, perborates and mineral peroxides and basifying agents such as ammonia, monoethanolamine, in various supports, such as creams, shampoos, oils, gels, powders and poultices.

 These state-of-the-art methods have a drawback, however, because the fading or lightening of the dye is also accompanied by discoloration, that is to say destruction of the natural pigments of the hair.

 These treatments therefore do not make it possible to return to the natural color of the hair when it has been previously dyed. This is particularly troublesome for gray hair which is a mixture of unpigmented hair and pigmented hair. In this case, we do not find after treatment, the white hair and the original pigmented hair, but slightly yellowed white hair and partially discolored pigmented hair, which gives the hair a color turning yellow, little aesthetic and artificial.

 In addition, the destruction of natural pigments is accompanied by damage to the hair which one wishes to avoid.

 The object of the invention is therefore to remedy the drawbacks mentioned above.

 The present invention relates to a process for lightening or erasing the color of dyed hair while preserving their natural color (pigmentation).

 A subject of the invention is also the compositions intended to be used in this process.

 The process according to the invention for lightening or erasing the coloring of dyed hair is essentially characterized by the fact that an acid solution of potassium permanganate is applied to dyed hair, and in a second step, a solution of a reducing agent chosen from sodium bisulfite, sodium hydrosulfite, cysteine, oxalic, thioglycolic, citric and ascorbic acids, the two steps being optionally separated by rinsing and the second step possibly being followed by a final oxidizing rinse to remove the last traces of reducing agent, this rinsing being carried out with a solution of hydrogen peroxide titrating from 0.5 to 5 volumes and preferably 1 to 3 volumes and whose bp is less than 7.

 According to a variant of the method according to the invention, the first step can be carried out in two phases, one of which consists in impregnating the hair with an acid solution, and the other in an application of a solution of potassium permanganate, the two stages being optionally separated by rinsing.

 The acid solution preferably applied in the first phase contains hydrochloric acid or sulfuric acid at a pH varying between 1 and 3.

 When an acid solution of potassium permanganate is applied in the first step, its pH varies between 1.5 and 4.

 The solution of reducing agent applied in the second step is preferably acidic or neutral and its pH varies between 1 and 7.

 Preferably used oxidizing solutions containing 0.01 to C, 5 mole / liter of potassium permanganate and preferably 0.01 to 0.2 mole / liter.

 The reducing agent is preferably used in concentrations ranging from 0.02 mole to 1 mole / liter and preferably between 0.04 and 0.8 mole / liter.

 The molar ratio of the reducing agent to potassium permanganate is preferably greater than 2 and in particular equal to or greater than 4.

 The exposure time of each of the solutions used in this process varies between 1 and 20 minutes and preferably between 1 and 10 minutes.

The lightening or erasing method according to the invention is applicable to hair dyed according to various methods and in particular
10 / hair dyed with compositions containing, in a cosmetically acceptable medium, precursors of oxidation dyes of the para or ortho type optionally combined with couplers.

 The precursors of para-oxidation dyes are chosen in particular from paraphenylenediamines, paraaminophenols and heterocylic bases of the 2,5-diaminopyridine or 2,4,5,6-tetraaminopyrimidine type.

 The precursors of ortho oxidation dyes are chosen from orthoaminophenols and ortho phenylenediamines.

 The couplers belong to the classes of phenols, naphthols, diphenols, metaphenylenediamines, metaaminophenols, heterocyclic couplers derived from sesamol, benzomorpholine or even indole couplers.

 The hair is generally dyed with compositions containing from 0.01 to 5% by weight of oxidation dye (s) precursor (s) of the para or ortho type and O to 5% by weight of couplers.

 These compositions, as is well known in the state of the art, are mixed just before use with an oxidizing agent which can be a solution of hydrogen peroxide titrating from I to 40 volumes.

 20 / dyed hair by using compositions containing, in a medium suitable for dyeing and cosmetically acceptable, an indolic dye mono- or dihydroxylated and in particular 5,6-dihydroxyindole and / or its derivatives These dyes are generally used in proportions between 0.01 and 5% by weight, the revelation of the color on the hair being carried out either by oxygen in the air or by means of a chemical oxidizing system.

 Among the oxidizing systems, there can be used a solution of hydrogen peroxide, the periodic acid and its water-soluble salts, sodium hypochlorite, potassium ferricyanide, silver oxide, Fenton's reagent, oxide lead, ammonium persulfate.

It is also possible to use a solution of quinone derivative chosen from ortho- or parabenzoquinones, 1,2- or 1,4-naphthoquinones or 1,2- or 1,4naphtoquinones monoimines, these quinone derivatives being chosen so that the difference in redox potential Ei of 5,6-dihydroxyindole at pH 7 in phosphate medium on glassy carbon electrode by voltammetry, and the redox potential Eq of the quinone derivative determined at pH 7 in phosphate medium by polarography on electrode of mercury with respect to the saturated calomel electrode, ie such that AE = Ei
Eq 4,320 mV.

 The oxidizing system can also consist of iodide ions and hydrogen peroxide, the iodide ions being present in the composition containing the indole derivative and the hydrogen peroxide being applied in a subsequent step.

 It is also possible to use metal salts from groups III to VIII of the periodic table, these metal salts being applied before the composition containing the indole derivative. They are chosen in particular from copper, manganese, cobalt, iron and silver salts.

 These methods are known in themselves and are described, in particular in French patents and patent applications 1133594, 1166172, 1264707, 2390158, 2536993, 2252841, 2593061, 2593062, 2594331, 2595245, 2599970, 2606636, 2613221, 2615730, 2615731 , 2618070, 2624730, 2625435, 2626173, 2626771, EP-0337853, 0348280, 0350385, 89 / 402311.8, FR-89/11814.

 3 "/ the hair can also be dyed with direct dyeing compositions containing, in a cosmetically acceptable medium, the direct dyes chosen from nitro benzene derivatives (aromatic amines, aminophenols, phenols or nitro polyphenols), azo dyes , anthraquinone dyes, azine dyes.

These direct dyes are generally used in amounts of between 0.1 and 5% by weight relative to the total weight of the composition. Dyeing is carried out in this case without the addition of an oxidizing agent.

Such methods are known in themselves and are described in particular in "The Science of Hair Care"
Charles Zviak - Marcel Decker Inc. 1986.

 It is possible to determine the degree of lightening or fading of the coloration by evaluating the color of the hair, dyed or natural, by measurements in the colorimetric system 1, a, b.

 According to this colorimetric system, a color is defined by three parameters: L indicating the intensity, a the component of the color along the red-green axis, b the component of the color along the yellow-blue axis.

 A color is light when it has a high L value and dark when the value of L is low.

 Likewise, the redder a color, the higher a, the more yellow a color, the higher b.

It is estimated that a lightening or fading of the color is obtained without having discoloration of the natural hair when the values of
L and b approximate those of natural hair color. On the other hand, in the case of discoloration, an increase in the parameters is observed
L and b compared to the values determined on natural hair.

 The process according to the invention is particularly useful for recovering after a dyeing, the natural color of the hair or then for lightening a dye which is too dark, without however damaging the hair.

 An object of the invention is also constituted by the erasing or lightening agent used which comprises several separate components which can be stored in devices with several compartments, such as "lightening" or "kits". erasing of the coloring.

 According to an implementation of the invention, this agent comprises a first component consisting of an acid solution of potassium permanganate and a second component consisting of a solution of a reducing agent chosen from sodium bisulfite, sodium hydrosulfite, cysteine, oxalic, thioglycolic, citric and ascorbic acids; this agent possibly comprising a third separate component consisting of an oxidizing agent intended to eliminate the last traces of reducing agent.

 According to a variant of the invention, the erasing or lightening agent with several separate components comprises a first component containing an acid solution having a pH of between 1 and 3, a second component containing a permanganate solution of potassium, a third component containing a solution of a reducing agent chosen from sodium bisulfite, sodium hydrosulfite, cysteine, oxalic, thioglycolic, citric and ascorbic acids.

 According to the invention, the solution containing potassium permanganate has a pH preferably between 1.5 and 4.

 The solution containing the reducing agent preferably has an acidic or neutral pH, between 1 and 7.

 The oxidizing solution contains from 0.01 to 0.5 mole / liter of potassium permanganate and preferably from 0.01 to 0.2 mole / liter.

 The reducing agent is present in the solution in proportions of 0.02 mole to 1 mole / liter and preferably between 0.04 and 0.8 mole / liter.

The following examples are intended to illustrate the invention without, however, being limiting in nature.
EXAMPLE 1
Locks of natural gray hair are dyed with the following composition - 5, 6-dihydroxyindole 1.0 g - ethanol 10.0 g - sodium lauryl ether sulfate 1.0 g - water qs 100.0 g
The pH is adjusted to 8.5
After having allowed to stand for 10 minutes at room temperature, the hair is washed with shampoo, rinsed, then dried.

 They are dyed in a uniform gray color.

If we want to erase this color, we successively apply the following solutions
Solution a - RMn04 1.6 g (0.1M) - HCl 0, yin qs 100.0 g
pH = 1.7
Solution b - Sodium bisulfite 5.0 g (0.5M) - Water qs 100.0 g
pH = 4.8
Solutions a) and b) are applied for 3 minutes each and are separated by rinsing.

 After applying solutions a) and b), there is a significant lightening of the color.

 After three successive applications of solutions a) and b), an almost complete erasure of the color is observed.

EXAMPLE 2
The dye is identical to that of Example 1.

The lightening is carried out as follows
Solution a: 0.1N HCl solution Solution b: b - KMnOo 1.6 g (0.1 µM) - Water qs 100.0 g
pH = 3
Solution c - Sodium bisulfite 5.0 g (0.5M) - Water qs 100.0 g
pH = 4.8
The dyed hair is impregnated with solution a) for 1 minute; then the composition b) is applied for 3 minutes and finally the solution c) for 5 minutes.

 The hair is rinsed and dried.

 There is a significant lightening of the color.

EXAMPLE 3
Natural gray locks of hair containing 90% white hairs are dyed in two stages with the following compositions 1st stage - 5, 6-dihydroxyindole 1.0 g - Ethanol 10.0 g - Potassium iodide 0.7 g - Na lauryl ether sulfate 1.0 g - Water qs 100.0 g
The pH is adjusted to 5 by HCl
After leaving 10 minutes at room temperature, rinse.

2nd stage - Hydrogen peroxide 10 volumes
spontaneous pH = 4
After leaving for 10 minutes at room temperature, the hair is washed with shampoo, rinsed, and then dried.

 They are dark brown to brown.

If we want to clarify them, we successively apply the following solutions
Solution a - KMn04 1.6 g (0.1 µM) - 0.1N HCl qs 100.0 g
pH = 1.7
Solution b - 5% sodium bisulphite (0.5M)
pH = 4.8
These solutions are applied for 3 minutes each with an intermediate rinse and a final rinse. After three application cycles a), then b), the hair is lightened and has a light mahogany brown color.

EXAMPLE 4
Natural gray locks of hair at 90% white are dyed in two stages with the following compositions 1st stage - 5, 6-dihydroxyindole 1.0 g - Ethanol 10.0 g - Ammonium lauryl ether sulfate 1.0 g - Water qs 100.0 g
The pH is adjusted to 8.5 by NaOH
After leaving 10 minutes at room temperature, rinse.

2nd stage - Hydrogen peroxide 10 volumes
The pH is adjusted to 9.5 by NaOH
After having allowed to stand for 10 minutes at room temperature, which has the effect of deepening the coloring, the locks are rinsed and washed, which are then dark brown.

If we want to erase this coloring, we apply successively the following solutions
Solution a - KMnO4 0.4 g (0.25M) - 0.1N HCl asp 100.0 g
pH = 1.7
Solution b - Cysteine hydrochloride 5.0 g - Water qs 100.0 g
spontaneous pH = 1.9
The two solutions are applied for 3 minutes each with intermediate rinsing, rinsing and final shampoo.

 The hair is lightened and, if we apply two more cycles a) then b), we return to a very light shade: gray to ash blonde.

EXAMPLE 5
Natural gray hair strands with 90% white hairs are dyed in two stages by the following compositions 1st stage - 5, 6-dihydroxyindole 0.5 g - Ethanol 10.0 g - Sodium lauryl ether sulfate 1.0 g - Water qs 100 0.0g
pH = 8.5 Far NaCH
After leaving 11 minutes at room temperature, rinse.

2nd step - Benzoquinone 0.1 g - Water qs 100.0 g
spontaneous pH = 3.6
Leave on for 5 minutes, which has the effect of strengthening the coloring.

 After rinsing and shampooing, the hair is dyed brown.

 If solutions a) and b) are applied successively as described in Example 1, and this three times in succession, the initial gray shade of the hair is practically found.

EXAMPLE 6
Natural gray hair strands are pretreated with the following composition 1st time - CuS04 1.0 g - Sodium lauryl ether sulfate 1.0 g - Water qs 100.0 g
pH = 9.5 with monoethanolamine
After an exposure time of 10 minutes and a rinse, the locks are dyed with the following composition 2nd step - 5, 6-dihydroxyindole 1.0 g - Ethanol 10.0 g - Sodium lauryl ether sulfate 1.0 g - Water qs 100 0.0g
pH = 8.5 by NaOH
The locks are colored black.

 After three successive applications of solutions a) and b) as described in Example 1, the locks are lightened in a medium gray shade.

EXAMPLE 7
Locks of natural gray hair containing 90% white hairs are dyed with the composition of Example 1 for 10 minutes.

 A second application of this same composition is carried out again for 10 minutes.

 After rinsing and drying, the hair is dyed dark brown.

If we want to clarify them, we do three successive treatments with the following solutions
Solution a - KMnO4 1.6 g (0, lu) - 0.1N HCl qs 10G, O g
pH = 1.7
Solution b - Oxalic acid 2.0 g - Water qs 100.0 g
spontaneous pH = 1.1
at the rate of 3 minutes each, with intermediate rinsing, rinsing and final shampoo.

 After drying, the hair is lightened in a light golden brown.

EXAMPLE 8
Locks of natural gray hair containing 90% white hairs are dyed according to the method described in Example 7.

 The hair is dark brown.

If we want to clarify them, we do three successive treatments with the following two solutions
Solution a - KMnO4 1.6 g - 0.1N HCl qs 1CO, O g
Solution b - Thioglycolic acid 2.0 g - Water qs 100.0 g
spontaneous pH = 2.1
at the rate of 3 minutes each, with intermediate rinsing, rinsing and final shampoo.

 The locks are finally very light in a pinkish beige blonde color.

EXAMPLE 9
Natural gray hair strands with 90% white hairs are colored by the following composition - 5, 6-dihydroxyindole 0.5 g - Ethanol 10.0 g - Ammonium lauryl ether sulphate 1.0 g - Water qs 100.0 g
pH = 8 by NaOH
with an exposure time of 10 minutes.

 After rinsing and drying, a second identical application is carried out.

 The hair is dyed brown.

 They are then treated in order to erase the color with the following two solutions, for 3 minutes.

Solution a - KMnO4 1.6 g - 0.1N HCl qs 100.0 g
Solution b - Sodium hydrosulfite 5.0 g - Water qs 100.0 g
spontaneous pH = 4
with an intermediate rinse and a final rinse. This treatment is repeated two more times, and we end with a shampoo.

 The locks then have a light gray shade very close to their initial shade.

EXAMPLE 10
Locks of natural gray hair containing 90% white hairs are dyed, according to the method of Example 9, in brown.

In order to clarify the nuance, they are treated successively by the two solutions
Solution a - KMn04 1.6 g - 0.1N HCl qs 100.0 g
Solution b - Citric acid 5.0 g - Water qs 100.0 g
spontaneous pH = 2.5
with a pose of 3 minutes in each case, an intermediate rinse and a final rinse.

After three application cycles, the wicks are light brown
EXAMPLE 11
Locks of natural gray hair containing 90% white hairs are colored according to the method of Example 9.

They are colored in chestnut.

In order to remove the coloring, they are then treated successively for 3 minutes with the following two solutions
Solution a - KMnO4 1.6 g - 0.1N HCl asp 100.0 g
Solution b - Ascorbic acid 5.0 g - Water qs 100.0 g
spontaneous pH = 2.6
with intermediate and final rinsing.

 The locks are then very lightened in a light brown.

 After two other cycles of solutions a) and b), the locks returned to their initial gray hue.

2,0 g MA - Alkylsulfate de triéthanolamine vendu
sous la dénomination SACTOL LT 41 par
la Société LEVER 3,0 g - Diéthanolamide laurique 6,3 g - Acide éthylènediamine tétracétique 0,2 g - Hydroquinone 0,2 g - 3-méthyl 2-phényl 5-pyrazolone 0,2 g - Solution d'ammoniaque à 20% de NH3 10,5 g - Eau déminéralisée asp 100,0 g
Cette composition est mélangée au moment de l'emploi avec un poids égal d'eau oxygénée à 20 volumes.EXAMPLE 12
Natural gray locks of hair containing 90% white hairs are colored with an oxidation dye having the following composition - Paraphenylenediamine 0.80 g - Paraaminophenol 0.05 g - Resorcin 0.6 g - Metaaminophenol 0.05 g - Hydrochloride 2,4-diamino
phenoxyethanol 0.25 g - Oleic acid 19.0 g - Octyldodecanol sold under the
name EUTANOL G by the
HENKEL 8.5 g - Cetylstearyl alcohol sold under
the name EMULGIN B 3 by the
HENKEL 2.8 g - 2-amino 2-methyl propanol 10.5 g - Ethyl alcohol 10.0 g - Benzyl alcohol 10.0 g - Cationic polymer consisting of
patterns

2.0 g MA - Triethanolamine alkyl sulphate sold
under the name SACTOL LT 41 by
LEVER 3.0 g - Lauric diethanolamide 6.3 g - Ethylenediamine tetracetic acid 0.2 g - Hydroquinone 0.2 g - 3-methyl 2-phenyl 5-pyrazolone 0.2 g - 20% ammonia solution NH3 10.5 g - Demineralized water asp 100.0 g
This composition is mixed at the time of use with an equal weight of hydrogen peroxide at 20 volumes.

 Applied to gray hair for 30 minutes, it gives them, after rinsing and shampooing, a dark chestnut color.

If you want to lighten the color, the locks are treated successively with the two solutions
Solution a - KMnO4 1.6 g - 0.1N HCl qs 100.0 g for 12 minutes.

Solution b - Sodium bisulfite 5.0 g - Water qs 100.0 g
pH = 4.8 for 12 minutes, after an intermediate rinse.

 This treatment is repeated two more times.

 The dark brown locks at the start are dark ash blonde after the three cycles.

EXAMPLE 13
Locks of natural gray hair containing 90% white hairs are dyed with a direct dye having the following composition: 2-N-methylamino 4-ss-hydroxyethyloxy-
nitrobenzene 0.1 g 2-N-methylamino 4-ss- γ -dihydroxy-
propyloxynitrobenzene 0.5 g 2-N-ss-hydroxyethylamino 5-N, N-bis (ss-
hydroxyethyl) aminonitrobenzene 1.35 g 2-N-methylamino 5- (N-methyl N, ss, γ; -
dihydroxypropyl) aminonitrobenzene 0.9 g 4-amino 2'-methyl 4 '- (N, N-bis-13-hydroxy-
ethylamino) phenylazobenzene 0.15 g dye sold under the name
BLUE EXTRA CELLITON by BASF 0.14 g - Oleic diethanolamide 2.5 g Lauric acid 1.0 g Ethylene glycol monoethyl ether 4.5 g - Hydroxyethylcellulose sold under the
name NATROSOL 250 MR by the
AQUALON 1.25 g - 2-mole polyglycerolated oleic alcohol
of glycerol 3.2 g - Preservatives qs - Perfume as
Monoethanolamine qs pH = 9.5 - Demineralized water qs 100.0 g
Applied to gray hair for 30 minutes, it gives them, after rinsing, a deep brown color.

 If one wishes to erase the color, solutions 3 and a of example 3 are applied under the same conditions; the locks go from light brown to light gray.

EXAMPLE 14
Natural gray hair strands with 90% white hairs are dyed with a direct dye of the following composition - 2-amino 5-hydroxynitrobenzene 0.2 g - 2-N-ss-hydroxyethylamino 5-hydroxy
nitrobenzene 0.9 g - 2-N-ss-hydroxyethylamino 5-amino
nitrobenzene 0.07 g - 2-N-ss-amino monohydrochloride
ethylamino 4-methoxynitrobenzene 0.025 g - N-lauryl N-carboxymethyl N'-lauryl
N'-carboxymethyl 1,3-diaminopropane 9.5 g - Oleocetyl dimethyl chloride
hydroxyethyl ammonium 1.5 g - Lauric alcohol with 10 moles of oxide
ethylene sold under the name
HYDOL 100 by the company HENKEL 9.0 g - Glycol distearate 0.8 g - Diethylethanolamine cocoate
oxyethylenated to 4 moles of ethylene oxide 2.0 g - Citric acid 0.35 g - Carboxymethylcellulose sold under the
name BLANOSE 7 M 8 / SF by the
HERCULES 1.25 g - Preservatives qs - Perfume qs - Ammonia qs pH = 6 - Demineralized water qs 100.0 g
Applied for 30 minutes on natural gray hair, this composition gives them, after rinsing, a copper-red color.

 If it is desired to lighten the color, the solutions a and b of Example 3 are applied under the same conditions; the locks go from deep coppery blonde to light pinkish blonde.

EXAMPLE 15
Locks of natural gray hair containing 90% white hairs are colored by the following composition - 3-methyl 5,6-dihydroxyindole 1.0 g - ethanol 10.0 g - ammonium lauryl ether sulfate 1.0 g - water qs 100, 0 g
pH = 8.5 by NaOH
The exposure time is 10 minutes and a second identical application was made.

 After three erasing cycles applied according to the method of Example 3, the locks, which were bluish dark gray, are light greenish gray.

EXAMPLE 16
Locks of natural gray hair containing 90% white hairs are colored by the following composition - 2,3-dimethyl hydrobromide
5, 6-dihydroxyindole 2.0 g - Ethanol 10.0 g - Ammonium lauryl ether sulfate 1.0 g - Water qs 100.0 g
pH = 9 by NaOH
The application is repeated a second time, the exposure times being 10 minutes.

Three erasing cycles are carried out with the following solutions and exposure times of 3 minutes
Solution a - KMnO4 0.8 g (0.05M) - HCl 0.05N qs 100.0 g
Solution b - Sodium bisulphite 2.5 g (0.25M) - Water qs 100.0 g
The hair that was medium brown is ultimately ash blonde.

Claims (21)

 1. A method for erasing or lightening the dyeing of dyed hair, characterized in that one applies to dyed hair, in a first step, an acid solution of potassium permanganate, and in a second step, a solution of a reducing agent chosen from sodium bisulfite, sodium hydrosulfite, cysteine, oxalic, thioglycolic, citric and ascorbic acids.  2. Method according to claim 1, characterized in that the two stages are separated by a rinsing stage.  3. Method according to claim 1 or 2, characterized in that the second step is followed by a final oxidizing rinse to remove the last traces of the reducer  4. Method according to any of claims 1 to 3, characterized in that the first step is carried out in two phases, a first phase consisting of a prior impregnation of the hair with an acid solution followed, in a second phase, applying a potassium permanganate solution.  5. Method according to claim 4, characterized in that the two phases are separated by rinsing.  6. Method according to any one of claims 1 to 5, characterized in that the potassium permanganate solution has a pH between 1.5 and 4.  7. Method according to any one of claims 1 to 6, characterized in that the reducing solution is acidic or neutral and has a pH between 1 and 7.  8. Method according to any one of claims 1 to 7, characterized in that the oxidizing solution contains 0.01 to 0.5 mole / liter of potassium permanganate and preferably 0.01 to 0.2 mole / liter .  9. Method according to any one of claims 1 to 8, characterized in that the reducing solution contains 0.02 mole to 1 mole / liter and preferably between 0.04 and 0.8 mole / liter of reducing agent.  10. Method according to any one of claims 1 to 9, characterized in that the molar ratio between the reducing agent and the potassium permanganate is greater than 2 and preferably equal to or greater than 4.  11. Method according to any one of claims 1 to 10, characterized in that the composition applied at first is maintained in contact with the hair for a period of 1 to 20 minutes and preferably between 1 and 10 minutes and that the composition applied in the second step is maintained in contact with the hair for a period of 1 to 20 minutes and preferably 1 to 10 minutes.  12. Method according to any one of claims 1 to 11, characterized in that the hair has been previously dyed with a composition containing, in a cosmetically acceptable medium, precursors of oxidation dyes of the para or ortho type optionally associated to couplers, in the presence of an oxidant.  13. Method according to any one of claims 1 to 11, characterized in that the hair has been dyed beforehand with a composition containing in a cosmetically acceptable medium, at least one indolic dye, the development of the color having been carried out by the oxygen in the air or by a chemical oxidizing system.  14. Method according to any one of claims 1 to 11, characterized in that the hair has been dyed beforehand thanks to a composition containing at least one direct dye chosen from nitrobenzene dyes, azo dyes, anthraquinones, azine dyes.  15. Agent for erasing or lightening the coloring of dyed hair, characterized in that it comprises several separate components, a first component consisting of an acid solution of potassium permanganate, and a second component consisting of a solution containing a reducing agent chosen from sodium bisulfite, sodium hydrosulfite, cysteine, oxalic, thioglycolic, citric and ascorbic acids.  16. Agent according to claim 15, characterized in that the first component consists of two separate compositions, the first consisting of an acid solution and the second consisting of a solution of potassium permanganate.  17. Agent according to any one of claims 15 or 16, characterized in that the solution constituting the first component and containing potassium permanganate, has a pH between 1.5 and 4.  18. Agent according to any one of claims 15 to 17, characterized in that the second component containing a reducing solution has an acidic or neutral pH varying between 1 and 7.  19. Agent according to any one of claims 15 to 18, characterized in that the solution containing potassium permanganate contains 0.01 to 0.5 mole / liter and preferably from 0.01 to 0.2 mole / liter.  20. Agent according to any one of claims 15 to 19, characterized in that the solution containing the reducing agent contains 0.02 mole to 1 mole / liter of reducing agent and preferably 0.04 to 0.8 mole / liter.  21. Kit for erasing or lightening the coloring of dyed hair with several compartments, characterized in that it contains an agent as defined in any one of claims 15 to 20, the different separate components being stored in separate compartments.