- The Technological Centre of the Granite of Galicia (CTG) has developed a project of investigation with the fundamental aim to study the phenomenon of marked of the stone and his back cleaning.

- The CTG has established an Index of Global Sensitivity to the marked (Isg), whose value indicates the degree of susceptibility to the marked of the stones.

- The essays have realised in the Laboratory of the CTG, and the prototype of the team of cleaning, has been developed and manufactured in his Centre of Design.

ANTECEDENTS:

At present, the solutions to the marked accidental of the natural stone, go through treatments with products, more or less effective , that apply sometimes without the necessary rigour, with the frequent result of an excess of failures, no only by his fault of efficiency, but by his scarce permanence in the time. They are innumerable the web pages where offer remedies for the care and cleaning of the natural stone in front of accidental stains, the majority of them of commercial character.

Recently it has been approved a new European norm for natural stone: "EN 16301. Methods of essay for natural stone. Determination of sensitivity to the marked accidental". This norm contemplates some proofs of marked/cleaning with six agents of marked, as it came tinto, oil olive, instantaneous coffee, Ketchup, tail and file. To these, the CTG has added other fourteen, that have identified like agents whose negative performance on the stone is known, like rotulador, rubber to chew, artificial urine, oxides of iron, etc.

DEVELOPMENT OF THE PROJECT:

They have studied different varieties of natural stone commercially very known. Adding to this, the different superficial finishings that apply to the stone, including the treatments with chemical products, obtains a wide range of materials studied of very diverse nature.

The Centre of Design of the CTG, with the end to give answer to this technical need, has designed and manufactured a machine according to the specifications and prescriptions of said European norm, that allows the repeatibility and reproducibility of the essay.

Besides, with the intention to create a versatile machine, that allow to work with some distinct parameters to which marks the norm, has developed a programmable software that allows to control, for each essay, the number of cycles, the frequency and the amplitude of the route of the magnetics head.

RESULTS:

Between the most stood out results of this project, fits to signal that it has established the Index of Global Sensitivity to the marked (Isg), whose value indicates the degree of susceptibility to the marked and allows to realise comparative between different varieties of stone, superficial finishings or time of exhibition to the agents of marked.

Besides, the study of different varieties of stone in function of his petrography, has allowed to check the relation between his sensitivity to the marked and the porous system of the rock. The varieties with lower absorption and open porosity, are the less liable to the marked, and besides present better answer in front of the cleaning of permanent stains.

Another important result of this study has been that only the carbonated rocks (limestones and marbles) can present, in addition to changes of colouring, a superficial erosion, more or less intense, in front of the exhibition of some agents like the red wine.