The invention relates to a single- or multicoloured wa¬ ter paint, particularly for simulation, that is, a paint which does not have organic solvents and thus is ecologically acceptable, and which is particularly suitable for simulating the special aesthetic effects of plastering or coverings which can be produced with the use of materials of a decorative nature, that is, a paint which, when applied, can simulate coverings of plasterwork, wood, paper, marble, ornamental stones, leather, plastics materials and other materials.

Water paints comprising a dispersion or emulsion of an insolubilised macromolecular colloid in water are known from US-3,458,328, US-4,476,654 and EP-A-0 182 926, whose description is incorporated herein by reference.

The prior art comprises no paints with which anyone who is not a skilled painter can produce, in a simple and repeatable manner, aesthetic effects simulating cover¬ ings which up to now could generally be produced in a satisfactory manner only by the application of plaster or by the use of wood, paper, marble, ornamental ston¬ es, leather, plastics material or other material which, by its nature, is suitable to produce decorative sur¬ face effects due to patterns, colours or bas-relief; moreover, these effects could not be produced with the use of a single paint nor, on the other hand, could different effects be produced with the use of the same paint.

At the moment, in order to attempt to produce similar

aesthetic effects, it is necessary to use two or more single-coloured paints of different colours and to make use of professionals in the field who, what is more, should have wide experience and artistic sensitivity; this involves considerable cost with a risk of obtain¬ ing results which do not conform to the effects origi¬ nally envisaged and which, sometimes, cannot even be repeated to an appreciable extent from one wall to ano¬ ther.

As a result of the foregoing, there is a need to solve the technical problem of finding a paint which, during application and in dependence on the methods and tools used, can form coverings which simulate surfaces formed with plasterwork, wood, paper, marble, ornamental ston¬ es, leather, plastics materials and other materials without the need for any particular skill to achieve the desired aesthetic result; these effects should al¬ so be obtainable even with the use of a single paint.

The invention solves the aforesaid technical problem by providing a paint comprising a dispersion of a ma¬ cromolecular colloid in the form of agglomerations with dimensions tipycally of from 0.5 to 10 mm, which are obtainable by insolubilising a first macromolecular colloid or mixture thereof in a water dispersion of elemental particles obtained by insolubilising a second macromolecular colloid or mixture thereof in water in the presence of solid particles and a film forming emulsion polymer, said agglomerations being susceptible to break up into said elemental particles when subject¬ ed to shear stress conditions of usual paint applica¬ tion means.

According to a preferred embodiment, said elemental

particles are capable of retaining their individuality when the agglomerations are subjected to shear stress by application means such as a brush, a roller or spray guns, but are susceptible to break further into frag¬ ments when the agglomerations are subjected to the higher shear stress which may be generated by applica¬ tion means such as a spatula, a sponge or a plastering trowel.

The advantages achieved by the invention are that dif¬ ferent aesthetic effects can be produced easily, even with a single paint, by varying the method of applica¬ tion of the paint and the tool used and can be repeated where necessary so that even a non-professional painter can produce aesthetic effects which simulate coverings of plasterwork, wood, marble, paper, ornamental stones, leather, plastics material and other materials.

The macromolecular colloid used in the practice of the invention is preferably a hydrophilic anionic polyelec- trolyte or a non-ionic colloid.

Anionic polyelectrolytes include sulphonated, sulphated and carboxylated synthetic and/or natural linear poly¬ mers. Particularly preferred are carboxylated polysac- charides such as starch and cellulose, particularly carboxylated cellulosic materials, including carboxyal- kyl cellulose, such as carboxymethylcellulose, and car- boxyalkylhydroxyalkyl cellulose, such as carboxyalkyl- hydroxypropyl cellulose, and acrylic polymers.

Carboxylated starch and cellulose are preferred since they contain hydroxy groups which contribute to avoid full dehydration of the insolubilised colloid.

Non-ionic colloids include alkyl and hydroxyalkyl ethers of polysaccharides such as methyl cellulose, me- thylhydroxypropyl cellulose, hydroxyethyl cellulose. Preferred are polysaccharides having "vicinal" hydroxyl groups, that is hydroxyl groups in adjacent positions in the polysaccharide ring such as polygalactoglycanes (guar gum or locust bean gum) and ethoxylated or propo- xylated polygalactoglycanes.

Film forming emulsion polymers which are useful in the practice of the invention include modified vinyl poly¬ mers and acrylic polymers such as styrene-acrylic re¬ sins, vinyl-acrylic resins, pure acrylic resins, chlo- ro-vinyl polymers and vinyl-versatic resins.

Solid particles referred to herein, comprise organic and inorganic fillers and/or pigments having a particle size typically of from 0.2 to 40 micron, preferably from 10 to 20 micron, which may have different shapes. The solid particles provide a solid surface on which the colloid may be adsorbed and they should be selected in order to be non-reactive or chemically inert in the dispersion wherein they are introduced.

Preferred solid particles include silicates (kaolin, mica), barium sulphate, aluminum oxide, titanium dioxi¬ de, silica, Ca carbonate, inorganic pigments such as Fe oxide, Cr oxide and solid organic pigments such as phthalocyanines, carbon black and naphthol derivatives (e.g. naphthol red) and arylamides.

The process for preparing the water paints, according to the invention, comprises the steps of: a) contacting in water a first macromolecular colloid or mixture thereof with an insolubilising agent for

said colloid, in the presence of said solid particles and of a film forming emulsion polymer thereby to cause gelification or at least partial insolubilisation of said colloid on said solid particles and obtain a dis¬ persion of elemental particles in water, and b) insolubilising a second macromolecular colloid or mixture thereof with an insolubilising agent therefor in the presence of said water dispersion of elemental particles.

The step of insolubilising a colloid in order to provi¬ de a dispersion in water is known in the art and suit¬ able insolubilising agent for different colloids are described in literature. US-3,458,328 (cf. col.8, table I) provides an extensive listing of insolubilising agents for different colloids.

The procedure described in EP-A-0 182 962 to provide a water dispersion of non-soluble precipitated colour particles may as well be used.

In the process of the invention it is however preferred to carry out step a) by first dispersing said solid particles consisting of fillers and/or pigments in wa¬ ter containing a non-ionic wetting agent, which is pre¬ ferably selected from products of condensation of ethy¬ lene or propylene oxides and alkylphenols, such as C ₈ - C, ₂ alkylphenol, derivatives of ethoxylated or propoxy- lated fatty acids (e.g. polyethyleneglycol monolaurate) and ethoxylated acetylene derivatives.

The typical concentration of non-ionic wetting agent is from 0.1 to 0.5% by wt.

The concentration of solid particles in water is typi-

cally from 0.5 to 40% by wt.

In order to achieve as much as possible irreversible adsorbtion of the colloid on the solid surface, the colloid is introduced in the suspension of solid parti¬ cles in the absence of ionic surfactants which are com¬ petitive with the colloid in the adsorbtion on the so¬ lid surface.

The film forming emulsion polymer is typically present in a concentration of from 10 to 35% wt..

The concentration of the colloid, which is added, is from 0.5 to 7% by wt.

The colloid is insolubilised by means of addition of an insolubilised agent, as previously specified.

If the macromolecular colloid is an anionic colloid with carboxylic groups, the preferred gelling and/or insolubilising agents are one or more salts containing a polyvalent cation, particularly organic or inorganic salts of Al, Fe, Cu, Ca, Ag and heavy metals.

If the macromolecular colloid used is a non-ionic col¬ loid with so-called "vicinal" hydroxyl groups, the pre¬ ferred gelling and/or insolubilising agents used are boric acid and organic titanates or zirconates such as alkanolamine or acetylacetonate titanate or zirconate, e.g. triethanolamine titanate.

The insolubilising step may be carried out in the pre¬ sence of a thickener. The preferred thickeners are non- ionic thickeners preferably modified by lipophilic groups, such as cellulose ethers modified with intro-

duction of lipophilic groups.

It is preferred to operate under conditions which cause only partial insolubilisation of the colloid, whereby, when carboxylated polysaccharides or acrylic polymers are used, the amount of insolubilising agent which is added is such as to not neutralize all the functional groups which make water soluble the original colloid.

In step b) , the dispersion of elemental particles pre¬ pared according to step a) , is used and a second col¬ loid or mixture of colloids is insolubilised in said water dispersion of elemental particles.

Preferably, the colloid used in step b) has the same chemical nature (that is anionic or non-ionic) or is the same colloid as that used in step a) . Preferably, a colloid is used having a molecular weigth above 400,000, more preferably above 500,000.

The colloid is insolubilised by further addition of an insolubilising agent or if an excess thereof has been used in the first step without further addition.

It has been found that the concentration in water of the solid particles, which act as reaction inhibitors and provide a solid surface on which the colloid is preferably irreversibly adsorbed and the nature of the colloid, play an important role in determining the dimensions and break up properties of the agglomera¬ tions into said elemental particles.

In order to obtain elemental particles having a dimen¬ sion of from 0.1 to 0.5 mm, it is preferred to use a concentration of solid particles in water of from 10 to

40% by wt. preferably together with a relatively low molecular weigth colloid.

In order to obtain elemental particles having a dimen¬ sion of from 0.5 to 2 mm and higher, solid particle concentration in water of from 0.5 to 5% by wt., is used preferably from 1 to 2% by wt. preferably together with a high molecular weigth colloid.

In the present description, high molecular weigth or high viscosity colloid is meant to indicate a colloid having preferably a molecular weigth above 500,000 and low molecular weigth or low viscosity colloid is meant to indicate a colloid having preferably a molecular weight below 100,000.

In the second step b) , it is preferred to use a high molecular weigth colloid in order to obtain coarse ag¬ glomerations; the colloid concentration is typically from 0.5 to 5% wt.. In step b) , a pigment may be added to the colloid to be insolubilised, typically in a small amount of from 0.05 to 0.1% by wt. in order to colour the external phase of the agglomerations; addi¬ tion of solid surface fillers should however be prefe¬ rably avoided.

A film forming emulsion polymer, as previously defined, may be added in step b) , preferably in the amount of from 2 to 20% wt referred to the overall composition.

If the reagents are mixed slowly during the formation of the gel and insolubilisation of the macromolecular colloid, agglomerations with dimensions of 0.5-10 mm, coloured by the pigments, are formed producing a sin¬ gle-coloured paint.

If two or more single-coloured paints are mixed toge¬ ther, a multicoloured paint is produced.

The dimensions of the particles into which the agglome¬ rations of the gel break up upon application are con¬ trolled by the solid particles of the pigments and fil¬ lers.

The dispersant phase of the paint may be coloured with transparent pigments or with water-soluble dyes of a colour different from that of the pigments in the gel particles in order to produce a paint which, once ap¬ plied, forms a covering constituted by a background co¬ lour on which the colour effects due to the pigments in the gel particles can be clearly distinguished.

According to the invention, it may be desirable to ob¬ tain agglomerations of elemental particles, having dif¬ ferent mechanical properties. A first type of agglome¬ rations may comprise a matrix which has a mechanical strength against breaking up into said elemental parti¬ cles which is not higher than the stress exertable by paint application means such as paint brushes and rol¬ lers. Such agglomerations are obtainable by using in step b) anionic macromolecular colloids, particularly carboxylated starch and cellulose, which are made inso¬ luble by means of metal cations as insolubilising a- gents, in order to obtain the matrix structure.

It may be desirable to obtain a second type of agglome¬ rations which have a matrix of higher mechanical strength, such that they are susceptible of being bro¬ ken up into particles only under the stress exertable by paint application means such as the spatula, the sponge or the plastering trowel. This latter type is

obtainable by using in step b), in order to obtain the matrix structure, non-ionic polymers such as particu¬ larly polygalactoglycanes (polygalactomannan) which are made insoluble by means of boric acid and/or organic zirconates or titanates.

The paints may comprise usual additives for paints, such as preservatives, biocides.

Examples of paints produced according to the invention are described below, the quantities of the components being expressed as percentages by weight and the compo¬ nents being indicated in a preferred order of addition. Examples 1-10 relate to the preparation of paints con¬ sisting of water dispersions of said elemental particl¬ es.

EXAMPLE 1

water to make up to 100 non-ionic wetting agent* from 0.01 to 0.5 preservative from 0.2 to 0.3 barium sulphate from 2 to 15 inorganic pigments from 10 to 15 low-viscosity sodium carboxymethyl cellulose from 1 to 5

2.5% non-ionic thickener with lipophilic groups in water from 5 to 10

2% high-viscosity sodium carboxymethyl cellulose in water from 0.75 to 2.5

10% aqueous solution of aluminium acetate from 1.5 to 5 vinyl versatate resins in

UtBST1TUTE SHEET

emulsion from 10 to 25

2% high-viscosity sodium carboxymethyl cellulose in water from 7 to 14

2.5% non-ionic thickener with lipophilic groups in water from 5 to 15

* e.g. nonyl phenol condensated with 12 moles of oxye- thylene.

The product is prepared by first dispersing in water the non-ionic wetting agent, the solid particles (ba¬ rium sulphate and pigments) and low-viscos'ity Na CMC.

In a second vessel a solution of the non-ionic thicke¬ ner and high-viscosity Na CMC is prepared in the amount required to provide the given concentration. In a third vessel a reactive medium is prepared comprising the in¬ solubilising agent (Al acetate) and film-forming poly¬ mer (polyvinyl-versatate) . The content of said third vessel is then poured into said second vessel under stirring and the resulting composition is poured into the water dispersion under stirring. High-viscosity Na CMC may further be added to avoid dehydration of the insolubilised colloid and a non-ionic thickener, selec¬ ted from those previously cited, may finally be added to control the reology properties.

EXAMPLE 2

The composition corresponds to that of example 1 where¬ in barium sulphate is substituted with mica (particle size from 5 to 20 micron) in the amount of from 2 to 13 % wt. referred to the overall composition. The product

may be prepared by means of the same preferred procedu¬ re of Example 1.

EXAMPLE 3

The composition corresponds to that of example 1 where¬ in barium sulphate is substituted with kaolin (particle size from 5 to 20 micron) in the amount of from 2 to 13 % wt. referred to the overall composition. The product may be prepared by means of the same preferred procedu¬ re of Example 1.

EXAMPLE 4

The composition corresponds to that of example 1 where¬ in barium sulphate is used in the amount of from 9 to 20% wt and organic pigments are used in the amount of from 1 to 3 %wt. The product may be prepared by means of the same preferred procedure of Example 1.

EXAMPLE 5

By following the procedure of Example 1, the following composition may be prepared:

water non-ionic wetting agent preservative barium sulphate inorganic pigments organic pigments in aqueous dispersion from 0.5 to low-viscosity sodium carboxymethyl cellulose from 1 to

2.5% non-ionic thickener

with lipophilic groups in water from 5 to 10

2% low-viscosity sodium carboxymethyl cellulose in water from 0.75 to 2.5

10% aqueous solution of aluminium acetate from 1.5 to 2.5 vinyl versatate resins in emulsion from 10 to 30

2% low-viscosity sodium carboxymethyl cellulose in water from 7 to 14

2.5% non-ionic thickener with lipophilic groups in water from 5 to 15

EXAMPLE 6

By following the procedure of Example 1, the following composition may be prepared:

water to make up to 100 non-ionic wetting agent from 0.01 to 0.30 barium sulphate from 3.5 to 12.4 inorganic pigments from 6.5 to 16 organic pigments in aqueous dispersion from 0.5 to 5 low-viscosity sodium carboxymethyl cellulose from 1 to 5

2.5% non-ionic thickener with lipophilic groups in water from 5 to 10

2% high-viscόsity sodium carboxymethyl cellulose in water from 0.75 to 2.5

10% aqueous solution of aluminium acetate from 1.5 to 5 vinyl versatate resins in emulsion from 20 to 25 carboxylated natural resins

(50%wt alkali solution) from 1 to 2 2% high-viscosity sodium carboxymethyl cellulose in water from 7 to 14

2.5% non-ionic thickener with lipophilic groups in water from 5 to 15

In the above composition, carboxylated natural resins such as rosin resin or shellac are anionic colloids which are added together with the vinyl versatate re¬ sins.

EXAMPLE 7

The following composition may be prepared according to the procedure of Example 1:

water to make up to 100 preservative from 0.2 to 3 barium sulphate from 2 to 12.4 inorganic pigments from 6.5 to 16 organic pigments in aqueous dispersion from 0.5 to 1 low-viscosity sodium carboxymethyl cellulose from 1 to 5 2.5% non-ionic thickener with lipophilic groups in water from 5 to 10 2% high-viscosity sodium

carboxymethyl cellulose in water from 0.75 to 2.5 branched polyacrylate from 0.01 to 1.3

10% aqueous solution of aluminium acetate from 1.1 to 5 vinyl versatate resins in emulsion 22 carboxylated natural resins from 1 to 2

2% high-viscosity sodium carboxymethyl cellulose in water from 7 to 14

2.5% non-ionic thickener with lipophilic groups in water from 5 to 15

EXAMPLE 8

The following composition may be prepared according to the procedure of Example 1, wherein acrylic resin emul¬ sion is used as film forming polymer:

water to make up to 100 non-ionic wetting agent from 0.01 to 0.5 preservative from 0.2 to 3 barium sulphate from 3.5 to 12.4 inorganic pigments from 6.5 to 16 organic pigments in aqueous dispersion from 0.5 to 1 low-viscosity sodium carboxymethyl cellulose from 1 to 5

2.5% non-ionic thickener with lipophilic groups in water from 5 to 10

4% high-viscosity sodium

SUBSTITUTE SHEET

carboxymethyl cellulose in water from 0.35 to 1.3 10% aqueous solution of aluminium acetate from 1.5 to 5 carboxylated natural resins (50% wt. alkali solution) from 1 to 2 acrylic resins in emulsion from 22 to 35 4% low-viscosity sodium carboxymethyl cellulose in water from 3.5 to 14 2.5% non-ionic thickener with lipophilic groups in water from 5 to 15

EXAMPLE 9

water to make up to 100 non-ionic wetting agent from 0.01 to 0.5 preservative from 0.2 to 3 barium sulphate from 2 to 12.4 inorganic pigments from 6.5 to 16 organic pigments in aqueous dispersion from 0.5 to low-viscosity sodium carboxymethyl cellulose from 1 to 2.5% non-ionic thickener with lipophilic groups in water from 5 to 10 2% high-viscosity sodium carboxymethyl cellulose in water from 0.75 to 5 10% aqueous solution of aluminium acetate from 1.5 to 5

vinyl versatate resins in emulsion from 22 to 35 carboxylated acrylic styrene resins from 1 to 2 2% high-viscosity sodium carboxymethyl cellulose in water from 7 to 14 2.5% non-ionic thickener with lipophilic groups in water from 5 to 10

The products of Examples 1 to 9 are single-coloured paints which comprise a water dispersion of said ele¬ mental particles having a dimension of from 0.1 to 0.5, which can be applied singly or mixed with each other at least by spraying, with a roller, with a brush or with a spatula.

According to the invention, such products are used for preparing paints comprising agglomerations susceptible of breaking up when applied. In view of the relatively high amount of fillers and/or solid pigments, the ag¬ glomerations obtained therefrom break up, when applied, into relatively small elemental particles having a di¬ mension in the above-quoted range.

In these paints, the sodium carboxymethyl cellulose constitutes the anionic macromolecular colloid, the aluminium acetate is the insolubilising agent, the ba¬ rium sulphate, the mica and the kaolin are the solid fillers, the carboxylated natural resins and the carbo¬ xylated acrylic styrene resins reduce the stiffness of the gel; the vinyl versatate resins are preferred since they keep the pH of the colloidal dispersion within the acid range in order to prevent the formation of sodium

SUBSTITUTE SHEET

aluminate.

Further examples of formulations of the paint according to the invention are given below.

EXAMPLE 10

A dispersion of coarse elemental particles is produced according to the following:

1% high-viscosity sodium carboxymethyl cellulose in water 69.5

50% solid pigment in aqueous dispersion 2

50% solid vinyl versatate emulsion 7

25% aqueous solution of calcium acetate 2.5

10% solution of aluminium acetate 1.25 2% high-viscosity sodium carboxymethyl cellulose in water 17.5

The product thus produced is in the form of a dense ge¬ latinous mass.

If the product is mixed with another of the same compo¬ sition, or two or more such products of different co¬ lours, are mixed slowly, a dispersion of elemental par¬ ticles is obtained having a dimension typically of from 0.5 to 2 mm.

In this example, the sodium carboxymethyl cellulose re¬ presents the anionic macromolecular colloid, and the calcium acetate and the aluminium acetate are the inso¬ lubilising agents.

EXAMPLE 11

Paints consisting of agglomerations in water, according to the invention, are obtained according to the follow¬ ing composition, wherein the components are listed in the preferred order of addition:

water to make up to 100 high-viscosity sodium carboxymethyl cellulose 1-2 product of examples 1 to 9 10-40

50% solid vinyl versatate emulsion 5-10 branched sodium polyacrylate up to 0.8

25% aqueous solution of calcium acetate 2.5-5

10% aqueous solution of aluminium acetate 1-2 2% high-viscosity sodium carboxymethyl cellulose 10-25

The paint thus produced is in the form of a dense gela¬ tinous mass.

If the paint is mixed with another of the same composi¬ tion, or two or more such paints of different colours, are mixed slowly agglomerations of gels are produced and, upon application, these break or split up as a re¬ sult of the forces exerted by the tool used, giving ri¬ se to single-coloured spots of colour in graduated sha¬ des, or to multicoloured spots of colour, also in gra¬ duated shades, if a mixture of two or more paints of different colours is used.

The paints produced according to the present example may also be mixed with a paint produced according to one of Examples 1 to 9 to obtain, upon application, a surface with spots of colour on a background which in turn is coloured.

SUBSTITUTE SHEET

In this example, the sodium carboxymethyl cellulose. and the sodium polyacrylate represent the anionic macromo¬ lecular colloids and the calcium acetate and the alumi¬ nium acetate are insolubilising agents.

EXAMPLE 12

water make up to 100 high-viscosity sodium carboxymethyl cellulose from 1 to 2 product of example 10 from 5 to 20

50% solid vinyl versatate emulsion from 5 to 10

25% aqueous solution of calcium acetate from 2 to 4

10% aqueous solution of aluminium acetate from 1 to 2.5

2% high-viscosity sodium carboxymethyl cellulose from 10 to 25

The paint thus produced is in the form of a dense, transparent, gelatinous mass containing the coloured particles of paint.

If the paint is mixed with another of the same composi¬ tion, or two or more paints of different colours, are mixed slowly, agglomerations with dimensions up to 10 mm are produced.

The paints produced according to the present example may also be mixed with a paint produced according to one of Examples 1 to 9 formed with transparent pigments or without pigments, to produce, upon application, a surface constituted by a dispersion of coloured parti¬ cles on a transparent or slightly coloured background.

SUBSTITUTE SHEET

EXAMPLE 13

A product according to the invention is obtained accor¬ ding to the following procedure:

COMPOSITION A

water 53.7 calcium carbonate (powder) 2-30 galactomannan 0.8-1.5

50% acrylic styrene resin emulsion 18 coalescent (a mixture of carbonyl ethers) 0.3 preservative 0.2

An organic and/or inorganic pigment dispersion and in¬ solubilising agents are added to composition A, which contains a non-ionic macromolecular colloid with so- called vicinal hydroxyl groups, that is, galactomannan, to produce composition B constituted by a resilient, gelatinous mass.

COMPOSITION B

composition A 94.5 organic and/or inorganic pigment dispersion 2.8 triethanolamine titanate 1.9-4

1.5% solution of boric acid 0.8-1.5

The triethanolamine titanate and the boric acid are the insolubilising agents.

The calcium carbonate in the composition A has the ef¬ fect of making the gel more resistant to forces which tend to break it up.

A gelatinous mass is obtained which is then dispersed in a vehicle having the following composition to provi¬ de dispersion of elemental particles in water.

VEHICLE

1% high-viscosity sodium carboxymethyl cellulose in water 46.5

50% acrylic styrene emulsion 23.10

10% aqueous solution of NaOH 4.6

10% aqueous dispersion of aluminium silicate 23.10

3% aqueous solution of boric acid 2.70

The thus obtained dispersion of elemental particles is introduced into the following composition:

water to make up to 100 galactomannan 0.8-1.5 50% acrylic-styrene resin emulsion 18

and the obtained product is introduced in the above- mentioned composition B in replacement of composition A; upon gently mixing a dispersion comprising agglome¬ rations is obtained.

When in composition A a relatively high amount of Ca carbonate or other suitable solid powder is used (e.g. 25-30%), paints are obtainable which provide an emboss¬ ed surface when applied. Low amounts of Ca carbonate provide paints giving smooth surfaces.

It may be desirable to mix with each others gels having the same or different colour as obtained according to

composition B of Example 13, prior to their introduc¬ tion into the vehicle. This operating procedure allows to obtain elemental particles having increased homoge¬ neity in their average dimension.

Similarly, when it is desirable to obtain agglomera¬ tions having a more uniform average dimension, it is preferred to mix with each other gels having the same or different colour, e.g. obtained according to compo¬ sition B of Example 13, wherein composition A has been replaced by the obtained dispersion of elemental parti¬ cles.