WO2007086094A1

WO2007086094A1 - Method for the production of vitreous slabs

Info

Publication number: WO2007086094A1
Application number: PCT/IT2007/000058
Authority: WO
Inventors: Vittorio Bulgarelli
Original assignee: Vittorio Bulgarelli
Priority date: 2006-01-30
Filing date: 2007-01-29
Publication date: 2007-08-02
Also published as: ITRA20060004A1

Abstract

Method for the production of coloured slabs, said method comprising the steps of mixing vitreous particles with pigments in a liquid substance containing water to permit diffusion of the piments through the particles so as to obtain a pigmented suspension; putting said semifinished product (1) into a mould (11); eliminating said liquid substance from said pigmented suspension to obtain a semifinished product (1) substantially solid; raising the temperature of said semifinished product (1) to a determinate temperature in such a way as to obtain a slab (10) of determinate shape, substantially homogeneous and cuttable along substantially rectilinear lines; said method being characterized in that said step of eliminating said liquid substance from said pigmented suspension comprises absorption of said liquid substance by said mould (11).

Description

METHOD FOR THE PRODUCTION OF VITREOUS SLABS

DESCRIPTION

The present invention relates to a method for the production of vitreous bodies. In particular, the present invention relates to a method for the production of vitreous bodies, the method including the stages of forming at least one slab of determinate shape, capable of being cut for the production of tesserae of determinate shape, usable as in the execution of wall-claddings and/or mosaic compositions or similar products. BACKGROUND TO THE INVENTION

It is known that, in the field of the production of glass for mosaic applications or of tesserae for the production of particularly valuable floors, a method is used which includes charging a crucible with a mixture of glasses and colourants until the composition of the material has taken on the desired colouring. It is as well to point out that these operations of charging the crucible and assessing the colouration assumed by the mixture are carried out at a temperature of approximately 1300⁰C, which must be maintained substantially constant for technical reasons and to preserve the crucible in good condition over time.

Once the desired colour has been obtained, it is possible to proceed with pouring the vitreous material into the moulds to obtain semifinished products in the desired formats, and therefore of glass of the desired shade. In addition, it must be pointed out that this glass must necessarily undergo a thermal cooling cycle, so-called "tempering", in a controlled-temperature environment, in order to avoid the explosion of the vitreous material which would inevitably occur at the moment of cutting into tesserae. In order therefore to be able to carry out this production stage, it will be necessary, after removing the material from the crucible and then cooling it, to transfer it to a suitably-equipped oven. This requires setting up the production site for the installation of this equipment and, naturally, confronting the corresponding costs. Among the costs mentioned above, it is worth recalling those due to the space which must be reserved for the corresponding unit, and those due to the corresponding operating times.

In virtue of what has been described above, the subsequent production, using the same crucible, of a frit of a different shade from that which has just been poured will require the previous cleaning of the crucible, in order to reduce the risk of chromatic contamination of the new colour with the old.

In any case, this technique of cleaning does not allow complete freedom from being affected by the old colour for reasons connected with the management of the crucible which, as explained above, must be maintained at a substantially constant temperature. In order to at least partially obviate the unavoidability of cleaning the crucible, some people have thought of postponing fulfilment of the order until a sufficient number of mutually similar commissions have been received, and of grouping the orders in such a way as to schedule production with sequences of colours very similar to each other. It becomes possible to determine of the new colour while avoiding cleaning the crucible provided that pigments or coloured glasses are added to correct the colour of the molten material of the new melt of frit obtained by addition to the residue of the previous melt. It appears evident that the excessive randomness of the added material, the considerable but limited capacity of the crucible and, in particular, the craftsman-like nature of the method, mean that it will not always be possible to correct the final colour of the frit before the pour. In fact, because it is not possible to easily determine the residual quantity of molten frit inside the crucible after the pour, the colour shade of the latter, and especially the relationship between this residual colour and the precise colour which it is desired to obtain, it will not always be possible to determine the percentage of material or pigment to add in order to bring the assigned task to a conclusion with repeatability. This limits the application of this method to craftsmen, so- called "master glassmakers" whose technological education is the fruit of years of experience, and at all events this method remains affected by the disadvantages of not allowing the production of minimal quantities of material of a determinate colour, repeatable even years later. In addition, it is as well to point out that the application of this method prevents the simultaneous production of vitreous materials of different colour using the same equipment. In virtue of what is described above, the resolution of the disadvantages listed above represents a problem currently unresolved, which conditions the activities of mosaicists and mosaic floor makers, besides representing an interesting challenge which the applicant has decided to take up.

To solve the problems described above in relation to the management of a plant for the casting of vitreous substances at high temperature, and of a relative crucible of large dimensions, the ideas have been conceived both of altering the process of colouring the glass, in such a way as to carry out the corresponding operations at room temperature, and of reducing the dimensions of the crucibles and/or the moulds, in such a way as to make them easily replaceable at the end of each production process, to avoid the disadvantages connected with the presence of vitreous residues. For example, document JP5233909 describes a method for producing mosaic tesserae in coloured glass, starting from an inert liquid in which glass and colourant powders are mixed; this vitreous mixture is poured into a mould and the liquid phase of the mixture is eliminated by filtering at high pressure; the application of this high pressure furthermore has the object of adapting the mixture to the conformation of the mould itself. The formation of the vitreous slab, from which the tesserae are made, is finally completed by prolonged calcination. Unfortunately, this solution does not allow the making of limited quantities of tesserae of a particular colour at a cost within the reach of an individual mosaic craftsman, given that the high-pressure filtering of the liquid phase of the vitreous mixture requires the use of expensive machinery, which must be completely dismantled and washed between one stage of filtering and the next, to avoid the possibility of the residues of a particular colourant altering the colouring of each further mixture to be treated subsequently to the first. Furthermore, the washing of the filters and the respective machinery requires a process of purification of the waste water to avoid environmental contamination; the result of all these operations to be carried out on the equipment, some of which require operational times of several hours, is to contribute to keeping the costs of production of mosaic tesserae high, with the effects indicated above. For these reasons, this method is revealed as burdensome and not very practical; furthermore, the need to clean the machine at every change of colouring of the vitreous mixture prevents the possibility of using the same production line for making mosaic tesserae with more than one particular colour within a period of 24 hours. Production methods similar to those described above are known from the most recent patent documents EP1190993 and WO03/033424, where the principal difference with respect to document JP5233909 consists in the introduction of adhesive substances to the vitreous mixture, while this is still in the liquid phase; these adhesives have the object of fixing the colour to the glass particles and of making the vitreous mixture more homogeneous, especially in the presence of powders obtained by recycling glasses of different type. Clearly these methods also present the same disadvantages connected with the cost of the high-pressure filtering stage; furthermore, the possible presence of a residue of adhesive material prevents the production of mosaic tesserae or vitreous materials of sufficient quality to be used in the execution of valuable work. In addition, if it were feasible to eliminate the adhesive through the application of heat at high temperatures, it would not be possible to ignore the contribution to contamination of the atmosphere, which would necessitate adding a device for removing toxic fumes, and this device, besides increasing the costs of purchasing and running the plant, would make it possible to install the plant only in designated areas in accordance with the provisions of the competent authorities, areas which are normally remote from centres of habitation. In other cases, the idea has been proposed of minimising the running costs by resorting to a process of sintering glass powders contained in moulds; in particular, patent JP10265231 provides teachings for producing vitreous materials by mixing glass powder and a colourant directly inside a mould and subsequently sintering the vitreous mixture thus obtained. This method proves to be practical and apparently allows the production of even limited quantities of vitreous material at low cost, but it will be seen below that it presents a series of disadvantages. First of all, the mixing of particles of glass and of colouring pigments, performed substantially in a dry state, does not allow a homogeneous vitreous mixture to be obtained; furthermore, it is well-known that materials obtained by sintering, even if they are made of vitreous particles, do not present a homogeneous structure such as is typically obtained by vitrification; and this fact only permits the production of material which is unsuitable for use in the mosaic sector, due to the impossibility of cutting it so as to show regular surfaces, and into tesserae of substantially identical dimensions. Therefore, in virtue of what is described above, the availability of a method for the production of even limited quantities of mosaic tesserae of high quality at low cost, is a problem currently unresolved, which conditions the activities of mosaicists and mosaic floor makers, besides representing an interesting challenge which the applicant has decided to take up.

In consideration of the situation described above, it would be desirable to have available a method which, besides having the advantages connected with mixing the particles and colourants at room temperature and in the liquid phase, avoids the costs and the problems connected with the use of a high-pressure filtering plant, the removal of the adhesive residues, and the disposal of liquid and gaseous waste products; such a method would allow the disadvantages typical of the known state of the art, explained above, to be limited and if possible

^' overcome, and in addition would permit the production of frits of determinate colours and in minimal quantities, such as to be accessible even to amateur mosaicists, and make possible the execution of works which hitherto are only realisable with the techniques of painting and not of mosaic.

SUMMARY OF THE PRESENT INVENTION The present invention relates to a method for the production of vitreous bodies. In particular, the present invention relates to a method for the production of vitreous bodies, the method including the steps of forming at least one slab of determinate shape, capable of being cut for the production of tesserae of determinate shape, usable for the execution of wall-claddings and/or mosaic compositions or similar products.

An object of the present invention is to provide a method which permits the resolution of the disadvantages set forth above, and which is capable of satisfying a series of requirements to which in the present state of affairs there is no answer, and therefore of representing a new and original source of economic advantage, able to alter the current market for mosaic tesserae, mosaic floors, and works of art which require the application of the technique of shading the subjects represented.

According to the present invention a method is provided for the production of vitreous bodies, and the principal characteristics of this method and of the products which can be obtained through this method will be described in at least one of the claims which follow.

A further object of the present invention relates to the production of a body in coloured glass or to any other glass or plastic product which is obtainable in the same way.

According to the present invention, furthermore, a body in coloured glass is produced for mosaic or flooring uses, the principal characteristics of the body itself being described in at least one of the claims which follow. The present invention, furthermore, refers to an apparatus for the application of the production method for vitreous bodies.

According to the present invention, furthermore, an apparatus is created for the application of the production method for vitreous bodies, the principal characteristics of this apparatus being described in at least one of the claims which follow.

BRIEF DESCRIPTION OF THE DRAWINGS Further characteristics and advantages of the product according to the present invention will appear more clearly from the following description, explained by reference to the attached drawings which illustrate some non-limiting examples of embodiment, in which identical or corresponding parts of the device itself are identified by the same reference numbers. In particular:

- figure 1 is a schematic perspective view of a first tool for the operation of a method according to the present invention during the execution of a respective operative stage;

- figure 2 shows figure 1 in transverse section and on an enlarged scale;

- figure 3 illustrates a plurality of second tools for the operation of the method according to the present invention during- the execution of a further operative stage; figure 4 is a schematic perspective view of a product which can be made by the method according to the present invention. DETAILED DESCRIPTION OF THE PRESENT INVENTION

Figure 1 illustrates a semifinished product 1 at a step necessary for the operation of a method for the production of coloured frits usable for the technique of mosaic or for wall or floor cladding. The method provides for the formation of the semifinished product 1 in vitreous material, substantially granular and coloured in advance, inside an apparatus of determinate shape. Here and in what follows, for practicality, this apparatus will include a mould 11 of determinate shape usable for producing semifinished products 1 according to a technique which will be explained below. According to the method in question, each semifinished product 1 will be taken to a sufficient temperature to aggregate the vitreous material in such a way as to confer continuity and structural homogeneity on the finished product, typically a slab 10 in glass, of determinate shape and dimensions. For practicality, but without constricting the potential of the present method, moulds 11 can have a substantially rectangular shape. In detail, the method in question includes the steps of mixing the vitreous particles in the form of granules, or rather of very fine powder, with pigments of determinate nature, and of allowing the pigments to diffuse among the particles of glass, carrying out this mixture in a determinate liquid. The result is the obtainment of a suspension of pigmented vitreous particles in a liquid environment, or more succinctly, a pigmented suspension.

Normally, the pigmented suspension results from the mixture of 60-75 parts of liquid by weight and 100 parts of vitreous particles. It is also as well to observe that excellent results have been obtained using 67 parts of liquid.

For convenience and containment of costs, this liquid may, without this representing a limitation, include water or be essentially composed of water.

At this point, when the mixing is finished, the pigmented suspension may be poured into a mould 11 of determinate shape, to confer on the vitreous substance a determinate shape, following the elimination of the water which was necessary for the colouring of the vitreous particles, thus creating the semifinished product 1 which, as has been said, is capable of being aggregated or vitrified. The mould 11 includes at the bottom a base 12 and is delimited upwards by a surface 15 visible in figure 2. Every mould 11, or at least the portion of it which lies below surface 15, is normally made of alabastrine gypsum which, as is well-known, is a material capable of absorbing water in considerable proportions, or of a material with similar liquid-absorbing properties.

If it is considered appropriate, the whole of mould 11 may be made of alabastrine gypsum. That would certainly contribute to simplifying the production technology of moulds 11. At times it may be advisable for surface 15 to be shaped so as to reproduce in negative the shape which is to be assigned to slab 10, without thereby introducing limitations to the present invention.

It is as well to point out that slab 10 will be made up of homogeneous glass, which may be cut along substantially rectilinear lines for the production of small pieces delimited by regular surfaces both in the event that mould 11 is suitable for bearing the high temperatures in which vitreous aggregation takes place, and in the event that the vitreous aggregation which semifinished product 1 must undergo takes place inside a crucible 14. This crucible 14, visible in figure 3, must be suitably prepared for conferring the desired shape on the corresponding slab 10 and permitting its subsequent removal, as will be more fully described below. Each slab 10 therefore will be usable for producing mosaic tesserae 30 visible in figure 4. Consequently, here and below, with reference to the vitrification stage, the terms ^λmould' and ^Λcrucible' may be found used interchangeably, depending on the context, unless indicated otherwise. It is appropriate to observe that the vitreous particles in powder form may include preferably, but without limiting effect, particles of vitreous borosilicate compounds, of the type that can be used for making phials for medicines or heat-proof oven dishes, or recycled glass made by finely grinding products in such materials. As is well-known, such glasses have a high degree of hardness and good capacity for maintaining colour stability, and are extremely easy to cut, allowing the use of an ordinary diamond glass-cutting tool for obtaining rectilinear cut surfaces. This allows it to be used instead of the mosaic hammer, avoiding wastage of material due to inexperience in the use of this tool. In addition, these types of glass maintain the characteristics described above even after subsequent re-firing, and react with the aggregation of the powder to produce a slab 10 in perfectly homogeneous glass, taking its shape in negative from the respective container/crucible 14 at a temperature of about 900⁰C, which must necessarily be reached in the furnace, and therefore at a lower temperature than a normal vitrification temperature which is not usually less than 1300⁰C. This obviously allows considerable savings in energy, and lower specifications for the furnace in which the procedure is to be carried out, at least in terms of the respective thermal insulation of the inner chamber.

It should be noted that the step of forming the pigmented suspension in a mould 11 of determinate shape includes the step of eliminating the water from the vitreous substance contained in mould 11. In this- way it is possible to obtain a semifinished product 1 which has dimensions such as to allow its insertion into the crucible 14. It is as well to point out that the step of eliminating the water includes the step of allowing the water to be absorbed by the alabastrine gypsum of the mould 11 at a controlled temperature of 40°C-50°C, and the step of bringing about the evaporation of the residual water. The latter is normally, but without limiting force, effected by transferring the semifinished product 1 to a crucible 14 which' is inserted into a furnace where its temperature is raised. This raising of the temperature can lead the semifinished product 1 to take on a controlled temperature which may conveniently but without limiting effect be between 60⁰C and 80⁰C. This step of bringing about the evaporation of the residual water by raising the temperature to a controlled value, below the boiling-point of water, is usually effected inside the same furnace as will later be used for the vitrification of the semifinished product 1. This step of evaporating the residual water is therefore comparable to a pre-heating step, preparatory to the subsequent raising of the temperature to which the semifinished product 1 must be subjected to produce the slab 10. This raising of the temperature must in fact be carried out in a gradual manner to preserve the physical and chemical characteristics of the glass which is being processed.

To facilitate the step of transferring the semifinished product 1 from the mould 11 to the crucible 14, the step of pouring the pigmented suspension into the respective mould 11 is preceded by a step of coating the surface 15 with a film P useful for facilitating the withdrawal of the semifinished product 1 itself from surface 15 which internally delimits mould 11. This film P, which may advantageously made in a porous material in order not to obstruct the absorption of water by the mould 11, also has the function of keeping the vitreous particle of the semifinished product 1 separate from the alabastrine gypsum of the mould 11. It should be borne in mind that the alkalis contained in the glass could cause chemical attack on the alabastrine gypsum of the moulds 11 during the production of the said semifinished product 1. Film P therefore allows this phenomenon to be avoided. This film P, visible only in figure 2, may advantageously be made of paper, preferably but without limiting effect of the type with high absorption capacity.

Each crucible 14 which is prepared for containing a respective semifinished product 1 during the heat treatment in the furnace has morphological characteristics which are such as to facilitate the removal of slab 10 at the end of the process. To this end, similarly to the description given with reference to mould 11, each crucible 14 is delimited upwards by a surface 15' shaped in negative so as to confer a determinate form on each corresponding slab 10, and such as to freely allow the execution of the step of placing a semifinished product 1 on surface 15' of a crucible 14. To this end, each crucible 14 / each surface 15' has a well 17' delimited laterally by internal sides 19', inclined with respect to well 17' by suitable angles 16' of draw, generally greater than those of mould 11, but always necessary to facilitate the removal of the contents, to be precise a slab 10. The step of placing a semifinished product 1 on surface 15' of a crucible 14 can be preceded by the step of coating surface 15' of the crucible 14, with a thickness S of anti-adhesive compound to facilitate subsequent operations of removal of slab 10 from the crucible. This step may conveniently, but without limiting effect, be performed by the use of an airbrush, also in order to accurately adjust the quantity of anti-adhesive substance, and therefore minimise the cost of applying this anti-adhesive compound.

It is as well to point out that this anti-adhesive compound must be such as to combine sufficient fluidity to be sprayed through an airbrush with the capacity to transform itself physically and chemically into a solid anti-adhesive crust as a result of the application of heat, and to remain removable at extremely low cost at the end of the production process. Otherwise, the crust could adhere closely to slab 10, damaging its structure or compromising its final quality. To avoid this disadvantage, and remain chemically and physically extraneous to the corresponding slab 10, the anti-adhesive compound to be sprayed onto the well 17' of each crucible 14 can be the result of the mixture of mineral substances and can validly include a mineral compound including 16 parts of magnesium carbonate

(MgCO3), 4 parts of zettlitz kaolin and 1 part of talc. The transformation of this mineral compound into a crust can occur at temperatures above 700⁰C, and in particular approximating by excess to the temperature of 1000°, or even above 1100⁰C, but it remains soluble in water, as a result of which it is easily removable at extremely low cost. It may be appropriate to point out that magnesium carbonate performs the function of refractory ballast inside the furnace, while kaolin is a clayey mass which makes the mineral compound plastic at the time of mixing and of its application by means of an airbrush, and at the same time performs a binding function to form the crust; the talc has a function predominantly as a lubricant and separator with respect to the glass of slab 10.

The step of bringing the semifinished product 1 contained in the crucible 14 to a temperature greater than or equal to a fusion temperature characteristic of the glass powder of the pigmented vitreous suspension occurs in a muffle furnace. This step may be preceded by a step of placing a plurality of crucibles 14 containing the respective semifinished products 1 inside the muffle furnace, in order to produce simultaneously a plurality of slabs 10, and therefore in such a way as to keep the corresponding semifinished products 1 separate from each other. In the event that the space in the muffle furnace is to be used so as to maximise the exploitation of the space, it will be advisable to make the crucibles 14 in such a way that they are stackable, leaving free the upper face 18 of the semifinished product 1 contained in the lower mould 11, which will become the free surface of the liquefied slab 10 and, subsequently to its cooling, the upper face of slab 10 itself. For ease of description, it is arbitrarily convenient to indicate this free surface of the liquefied slab 10 and the upper face of the solidified slab 10 by the same reference number, 18 to be precise.

In the latter case it will be important to have the use of loading doors for the muffle furnace of suitable dimensions for the moulds 11 or crucibles 14, on the basis of what has been said above, so that it is possible to load the furnace in such a way as to fill it to capacity, but also possible to remove the contents. In addition, it may be advisable to make crucibles 14 with the respective inner sides 19' shaped in such a way as to cooperate by juxtaposition with the external sides 21' of each crucible 14 and relating to the base 12' of each crucible in such a way that crucibles 14 are stackable on top of each other in orderly fashion to form stacks, as in figure 3, with surfaces 15' parallel to each other. Naturally the same could apply to the moulds 11 if it were desired to stack them.

It is as well to point out that the choice of the muffle furnace is fully justified by the fact that this is a relatively inexpensive piece of equipment, electrically powered and with an airtight closure, to avoid contaminating the external environment with fumes and/or dust. That makes this production method particularly clean, as there are virtually no emissions of vitreous gas to the outside of the furnace. The method is therefore usable not only in typically industrial contexts but even in workshops located in urban contexts where it would be totally impractical to think of passing the fumes through filters before emission into the atmosphere. This fact could allow the implementation of the method even by the individual mosaicist interested in vertically integrating their production process, given that the costs of production are markedly lower than those of currently known methods. The step of bringing each semifinished product 1 contained in the respective crucible 14 to a temperature greater than or equal to a fusion temperature allows the simultaneous aggregation/vitrification of vitreous substances of different shape and colouring, and naturally allows the maintenance of the distinctness of chromatic tonality predetermined for each semifinished product 1.

The step of aggregation/vitrification is associated with a step of sublimating part of the vitreous material of each semifinished product 1. When the sublimated glass in the form of gas cools down, it solidifies and remains inside the muffle furnace. This has the double advantage that this portion of glass is deposited in substantially uniform manner over the preformed pieces of glass, making them more brilliant, and at the same time avoids the dispersion of a polluting product into the atmosphere. This phenomenon of sublimation of the vitreous material is not normally accompanied by sublimation of the colourant, given that the colourants normally used in the glass industry are of low volatility and usually have a melting-point much higher than the temperatures of aggregation/vitrification of the vitreous particles used for the implementation of the present method. It is therefore possible, on the basis of specific individual requirements, to appropriately select the colourants used to obtain semifinished products 1 of distinct colouring, avoiding or otherwise the diffusion of the colourants in the vapour state, or a mixture of them, into the inside of the furnace as the temperature rises, and ensuring or otherwise the formation of surface areas of heterogeneous colouration. Besides, the use of a muffle furnace allows the production process of slabs 10 to be concluded with the necessary step of tempering taking place within the furnace itself and the reduction of processing times, because there is no step of removing the slabs 10 from the crucibles 14 and transferring them to a prepared environment with controlled temperature. As is obvious, in this way the investment required is minimised by the purchase of a simplified, and therefore less costly system, allowing the maximisation of the return on investment because of the possibility of concentrating several production steps within one determinate device.

As is well-known, glass is a substance not permeable to water, but the method described above teaches the production of slabs 10 of coloured glass in a way that is surprisingly simple, economical and safe, starting from a basic material including glass powder, and proceeding in such a way as to maintain the colouration conferred in a watery environment on the vitreous particles themselves as a result of the process of aggregation, so as to produce slabs 10 of homogeneous and uniformly coloured glass, both superficially and internally.

Finally, it is clear that modifications and variations may be made to the method here described and illustrated without for this reason departing from the protective compass of the present invention.

In any event, it is as well to point out that the slab 10 in vitreous material produced by the method described above is substantially homogeneous and cuttable along parallel planes by means of a diamond-point glass-cutting tool along substantially rectilinear lines in such a way as to allow the production of tesserae of homogeneous colour. Therefore, every slab 10 is usable to obtain mosaic tesserae delimited by regular profiles geometrically similar to each other or even substantially identical to each other.

It should be noted once again that the method in question is applicable by non-specialised, and therefore inexpensive personnel, and allows the simultaneous production of slabs 10 of a substantially infinite variety of different colours, reproducible with constant results by means of the same equipment, even at a considerable distance in time, so as to allow possible restoration of mosaic works already executed.

Claims

1. Method for the production of coloured frits; said method comprising the steps of mixing vitreous particles with pigments in a liquid substance containing water to permit diffusion of the pigments through the particles so as to obtain a pigmented suspension; putting said semifinished product (1) into a mould (11) ; eliminating said liquid substance from said pigmented suspension to obtain a semifinished product (1) substantially solid; raising the temperature of said semifinished product (1) to a determinate temperature in such a way as to obtain a slab

(10) of determinate shape, substantially homogeneous and cuttable along substantially rectilinear lines; said method being characterized in that said step of eliminating said liquid substance from said pigmented suspension comprises absorption of said liquid substance by said mould (11) .

2. Method according to claim 1, characterised in that said step of eliminating said liquid substance from said pigmented suspension takes place at a first controlled temperature.

3. Method according to claim 2, characterized in that said first controlled temperature is comprised between 40⁰C and 5O⁰C.

4. Method according to any of claims 1 to 3, characterized in that said step of eliminating said liquid substance from said pigmented suspension comprises a step of heating said pigmented suspension at a second controlled temperature for evaporating residual said liquid substance from the said semifinished product (1) .

5. Method according to any of claims 1 to 3, characterized in that said step of raising the temperature of said semifinished product (1) to a determinate temperature comprises a pre-heating step at a second controlled temperature for evaporating residual said liquid substance from the said semifinished product (1) .

6. Method according to claim 4 or 5, characterized in that said second controlled temperature is comprised between 6O⁰C and 80⁰C.

7. Method according to any of the preceding claims, characterized in that said mould (11) is made at least partially of a porous and/or liquid absorbing material.

8. Method according to claim 7, characterized in that said porous and/or liquid absorbing material comprises alabastrine gypsum.

9. Method according to any of the preceding claims, characterized in that said step of raising the temperature of said semifinished product (1) to a determinate temperature comprises the step of loading said mould (11) containing said semifinished product (1) into a furnace.

10. Method according to any of the claims 1-8, characterized in that said step of raising the temperature of said semifinished product (1) to a determinate temperature comprises the step of placing the said semifinished product (1) inside a crucible (14) and loading said crucible (14) containing said semifinished product (1) into a furnace.

11. Method according to any one of the preceding claims, characterized in that said step of raising the temperature of said semifinished product (1) to a determinate temperature comprise a step of sublimating part of the vitreous material of said semifinished product (1) in vitreous gas, which is followed by a step of cooling of said vitreous gas.

12. Method according to claim 11, characterized in that said step of sublimating part of the vitreous material of said semifinished product (1) takes place inside said furnace.

13. Method according to claim 11 or 12, characterized in that said step of cooling is followed by a step of glazing of said slab (10) inside said furnace by precipitation of said vitreous gas onto said slabs (10) .

14. Method according to claim 5 or any claims 6-13 in connection with claim 5, characterized in that said preheating step at a second controlled temperature takes place inside said furnace and is directly followed by said step of raising the temperature of said semifinished product (1) to a determinate temperature.

15. Method according to any of the preceding claims, characterised in that said step of raising the temperature of said semifinished product (1) to a determinate temperature is followed by a step of tempering said slab (10) inside said furnace.

16. Method according to claim 15 in connection with claim 13, characterised in that said step of tempering said slab (10) is realisable in said furnace in continuous succession to said step of glazing.

17. Method according to any of claims 10 to 17, characterized in that said furnace is an airtight furnace, to avoid contamination of the external environment.

18. Method according to any of the preceding claims, characterized in that said determinate temperature is greater than or equal to a vitrification temperature of said vitreous particles of said semifinished product (1) in order to product said slab (10) .

19. Method according to any of the preceding claims, characterized in that that said determinate temperature is greater than or equal to a temperature sufficient to obtain aggregation of said vitreous particles of said semifinished product (1) in order to product said stab (10) in homogeneous glass.

20. Method according to any of the preceding claims, characterized by comprising the ^■ step of arranging a film (P) of a porous material inside said mould (11) to keep said vitreous particles separate from the material of said mould (11), thus avoiding the occurrence of chemical reactions between the material of said mould (11) and said vitreous particles of said semifinished product (1) .

21. Method according to claim 20, characterized in that said porous film (P) comprises paper.

22. Method according to claim 21, characterized in that said step of placing said semifinished product (1) inside said crucible (14) comprises the step of coating the inside of said crucible (14) with an anti-adhesive compound to facilitate subsequent removal of the vitrified slab (10) obtained from said crucible.

23. Method according to claim 22, characterized in that said step of coating said crucible (14) with an anti- adhesive compound is carried out according to a technology similar to airbrush work, in order to accurately adjust the quantity of said anti-adhesive substance and minimize the cost of the operation.

24. Method according to claim 22 or 23, characterized in that said anti-adhesive material is of the type transformable into a solid anti-adhesive crust following application of heat; the resulting crust being removable completely from said slab (10) subsequently to the said step of raising the temperature of said semifinished product (1) to a determinate temperature.

25. Method according to claim 24, characterized in that said anti-adhesive material is such that the resulting solid crust is soluble and/or removable with water.

26. Method according to claim 24 or 25, characterized in that said anti-adhesive material includes a mixture comprising a first substance capable of performing the function of refractory ballast; a second substance capable of rendering such mixture plastic at ambient temperature in order to aggregate said mixture to form the crust at high temperature; and a third substance acting as lubricant- separator with respect to said slab (10) .

27. Method according to any of claims 22-26, characterized in that said anti-adhesive material includes a mineral mixture of magnesium carbonate (MgCO3) , zettlitz kaolin and talc.

28. Method according to claim 27, characterized in that that said anti-adhesive material results from the mixture of 16 parts by weight of magnesium carbonate (MgCO3) , 4 parts of zettlitz kaolin and 1 part of talc.

29. Method according to any of the preceding claims, characterized in that that said vitreous particles include preferably particles of recycled glass to minimize said determinate temperature.

30. Method according to any of the previous claims, characterized in that said pigmented suspension results from the mixture of 60-75 parts of liquid by weight and 100 parts of vitreous particles.

31. Method according to claim 31, characterized in that said pigmented suspension results from the mixture of 67 parts of liquid by weight and 100 parts of vitreous particles .

32. Method according to any of the preceding claims, characterized in that said vitreous particles include particles of boro-silicate glasses.

33. Method according to any of the preceding claims, characterized by comprising the step of cutting said substantially homogeneous slab (10) transversely along parallel planes by means of a glass-cutting tool to obtain mosaic tesserae delimited by regular profiles and substantially similar to each other.

34. Mould (11) adapted to carry out the method as claimed in claims 1 to 33; said mould (11) being delimited downwards by a base (12) and being delimited upwards by a surface (15) shaped in such a way as reproduce in negative a shape to be imparted to a semifinished product (1) to be transformed into a homogeneous stab (10) in glass; said mould (11) being characterized in that at least said surface is made at least in part of a porous, liquid absorbing material.

35. Mould (11) according 10 claim 34, characterized in that said material is alabastrine gypsum.

36. Mould (11) according to claim 35, characterised in that the mould (11) is made completely of alabastrine gypsum, to simplify the production technology.

37. Slab (10) in coloured vitreous frit produced through the method described with reference to claims 1-33, characterised by being cuttable transversely along parallel planes by means of a glass-cutting tool to obtain mosaic tesserae delimited by regular profiles and substantially identical to each other.

38. Crucible (14) for the application of the method described with reference to claims 1-33 for producing slabs

(10) like that described with reference to claim 33, said crucible (14) being characterised by being delimited upwards by a surface (15') shaped in negative to confer a determinate shape on each corresponding said slab (10) .

39. Crucible according to claim 38, characterised by having respective internal sides (19' ) and respective sides (21' ) shaped in such a way as to permit the formation of ordered stacks of crucibles (14) with internal surfaces (15') parallel to each other.