DESC:TECHNICAL FIELD OF INVENTION
The present invention relates to a method for oxidative dyeing a porous stone including marbles with indigo dye.

BACKGROUND OF THE INVENTION
Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. Marble is commonly used for sculpture, monuments or as a building material. Marble is naturally available in white, off white, yellowish white colour or green colour. After certain period of time, whiteness of marble decreases or white colour turns in dull white or yellowish that hampers aesthetic appeal thereof.
In normal practice, one can make attempt to dye marble or porous stones to give attractive look or colour. However, when the porous stone including marble is dyed, the colour remains on the surface of the marble temporarily as the stones or marbles do not allow the dye, air or water to pass or penetrate inside it or resist them to pass through and easily washes out in short time rendering bad appearance. Further, such objects do not hold any dye molecule on surface thereof or do not allow any dye molecule to pass there through.
Presently, indigo is used as a colour or dye in the textile industry only and is not used for dyeing objects such as porous stones, marbles and the like as chemical reaction of dye with surface structure is difficult. Even if it happens the dye does not penetrate to interior and may remain on top surface of the porous stone that gets easily removed or washes out.
Accordingly, there is need of a method for oxidative dyeing porous stone in order to give attractive and artistic look without compromising properties of porous stone such as crystalline structure and shine.

SUMMARY OF THE INVENTION
Accordingly, the present invention provides a method for oxidative dyeing a porous stone. In a first step, an oxidative dye solution is prepared. In the next step, the porous stone is kept immersed into the dye solution. In the next step, the porous stone is dried and then the dried porous stone is subjected to washing for removal of unfixed oxidative dye over the surface of the dyed porous stone.
According to an embodiment of the present invention, the dyeing solution comprises a dispersing agent from about 1.5 to about 5 GPL, an oxidative dye from about 25 to about 125 GPL, Caustic flakes from about 18 to about 95 GPL, Hydrosulphite from about 35 to about 155 GPL, Antifoaming agent from about 1.5 to about 5 GPL, Sequestering agent from about 0.5 to about 3 GPL and wetting agent from about 0.5 to about 3 GPL.
According to an embodiment of the invention, the oxidative dye is selected from sulfur dye and vat dye including indigo, anthraquinone etc.
According to an embodiment of the present invention, wherein the step washing includes cold washing alone or followed by hot wash.

BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows an indigo dyed marble dyed by a method of oxidative dying according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION
Although specific terms are used in the following description for sake of clarity, these terms are intended to refer only to particular structure of the invention selected for illustration in the drawings and are not intended to define or limit the scope of the invention.
In general aspect, the present invention herein after provides a method of oxidative dyeing of porous stones such as marble. The marble is composed of calcium carbonate crystal that is formed by re- crystallization process. The porous stone has a micro structure that consists microscopic inter crystalline spacing that may be defined as voids or as porous.
In accordance with a preferred embodiment of the present invention, the method of dyeing the porous stone comprises following steps:
In the first step, an oxidative dye solution is prepared by adding dispersing agent into the water, followed by addition of sequestering agent and wetting agent and then adding caustic and Indigo powder. The preparation takes place under continues stirring. The dyeing solution has alkaline pH. The oxidative dye is selected from sulfur dye and vat dye including indigo, anthraquinone etc.
In the next step, the porous stone is kept immersed into the oxidative dye solution for a predefined immersion time. The predefined immersion time may vary depending upon type of porous stone, porosity of the porous stone as well as in other alternative embodiments of the present invention. In this one preferred embodiment, the predefined immersion time is approximately 24 hours. In this step, the dye molecules penetrate inside the micro void structure of the porous stone and start aggregating trapped in the micro voids of the porous stone.
In the next step, the dyed porous stone is dried for a predefined drying time. In this one preferred embodiment, the predefined drying time is approximately twenty-four hours. The oxidative dyed porous stone may be dried in preferably in the natural weathering conditions. However, it is understood that the predefined drying time may vary depends on the type of the stone, weather conditions and the like. Further, it is understood that any other drying technique may he used for drying in alternative embodiments of the present invention including fans, hot air, dryers and the like.
In the further step, the dried marble is subjected to a cold wash followed by a hot wash in order to remove unfixed dye over the surface of the dyed porous stone. Due to micro porous structure of the porous stones the dye molecules are trapped into it, so it retains colour after wash giving a dye color shine to the marble without disturbing the original properties of porous stone such as crystalline structure and shine.
In accordance with an embodiment, the dyeing solution includes dispersing agent (Setamol WS) from about 1.5 to about 5 GPL, an oxidative dye from about 25 to about 125 GPL, Caustic flakes from about 18 to about 95 GPL, Hydrosulphite from about 35 to about 155 GPL, Antifoaming agent (Denim HS) from about 1.5 to about 5 GPL, Sequestering agent (IGSURF 3095 BD) from about 0.5 to about 3 GPL and wetting agent (IGSURF 3564 DA) from about 0.5 to about 3 GPL. The oxidative dye is selected from sulfur dye and vat dye including indigo, anthraquinone etc.
A composition of dyeing solution of the present invention facilitates dyeing of porous stone that lasts for long duration without fading. The dyeing solution of the present invention can be reused. A method of dyeing stones or marble of the present invention eliminates the use of expensive or complex techniques or machinery and providing aesthetic look to the porous stone that adds the value to the porous stone. Further, as the dye remains trapped in the porous structure, the possibility of becoming yellowish or dull of the porous stone including marble reduces.

EXAMPLES:
Various sizes of the marbles had been dyed according to the process as claimed in the application and tested by washing the dyed marble. Hereinafter, the present invention will be described in more detail based on an example. The example is not intended to limit the scope of the present invention. It is believed the invention will be better understood from the following detailed examples:
A marble stone of size 15” X 15” was dipped into indigo reduced solution having concentration as per Table 1 for 24 hours and dried it for naturally for one whole day. After drying the marble stone was washed with cold water followed by hot water to remove unfixed indigo dye. The marble having blue shade obtained by this method is shown in FIG. 1.
Ingredient Content in GPL
Dispersing agent 2.5
Indigo Powder 100
Caustic flakes 75
Hydrosulphite 125
Anti-foaming agent 5
Sequestering agent 2.5
Wetting agent 2.5

Table 1
It was observed that the blue shade of indigo gives a blue shine to the marble without compromising the properties of marble including crystalline structure of the marble. Also, the shine of the marble stone was as it is before the dyeing. Further, this dyed stone retained the colour even after washing hundred times.
The embodiments of the invention shown and discussed herein are merely illustrative of modes of application of the present invention. Reference to details in this discussion is not intended to limit the scope of the claims to these details. or to the figures used to illustrate the invention.
It is understood that various omission and substitutions of equivalents are on templated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the scope of the present Invention.
,CLAIMS:
1. A method for oxidative dyeing a porous stone, the method comprising the steps of:
preparing an oxidative dye solution;
immersing a porous stone into the dye solution for a predetermined period;
drying the marble for a predetermined period; and
subjecting the dried porous stone to wash to remove unfixed dye.

2. The method for oxidative dyeing a porous stone as claimed in claim 1, wherein the oxidative dye solution comprises a dispersing agent from about 1.5 to about 5 GPL, an oxidative dye from about 25 to about 125 GPL, Caustic flakes from about 18 to about 95 GPL, Hydrosulphite from about 35 to about 155 GPL, Antifoaming agent from about 1.5 to about 5 GPL, Sequestering agent from about 0.5 to about 3 GPL and wetting agent from about 0.5 to about 3 GPL.

3. The method for oxidative dyeing a porous stone as claimed in claim 1 or claim 2, wherein the oxidative dye is selected from sulfur dye and vat dye including indigo, anthraquinone etc.

4. The method for oxidative dyeing a porous stone as claimed in one of the preceding claims 1-3, wherein the predetermined time for immersion of the porous stone depends upon a type of stone, porosity of the stone and the like.

5. The method for oxidative dyeing a porous stone as claimed in claim 1 or 4, wherein the porous stone is immersed at around twenty-four hours.

6. The method for oxidative dyeing a porous stone as claimed in one of the preceding claims 1 - 5, wherein the porous stone is dried preferably in natural weathering conditions for a predetermined period.

7. The method for oxidative dyeing a porous stone as claimed in claim 1 or 6, wherein the porous stone is dried around twenty-four hours.

8. The method for oxidative dyeing a porous stone as claimed in claim 1, wherein the step washing includes cold washing alone or followed by hot wash.