The influence of moisture on the colour characteristics of natural stone

Abstract

The objects of the research are the facing elements of buildings and architectural monuments. The subject of the study is the process of changing the colour of the decorative stone from moisture. To solve the problems of analyzing the appearance of the surface, it is necessary to form a digital image of the surface of the facing stone and perform its processing by means of modern computer technology. Natural stone darkens in places where there is moisture in the pores. The paper investigated the component L, which is responsible for the lightness in the Lab colour system , the study was conducted on samples with a length of 600 mm and a width of 300 mm with a thickness of 24, 25, 31, 32 mm. To determine the humidity of the samples Hydro Condtrol device was used; it is based on the dielcometric method of measuring the humidity. After 100 hours of exposure to moisture at Pokostivsky granodiorite, the reduction of component L, which is responsible for the lightness in the Lab colour system, actually stops. There is a directly proportional dependence of the height of moisture rise in the samples of natural stone on their thickness, which is associated with an increase in the number of pores that participate in the liquid transfer process. With increasing duration of exposure to moisture at Pokostivsky granodiorite the moisture of the sample surface increases, which can be predicted in the general case and for different values of the thickness of the samples using analytical expressions. Comparison of intensity of value change of components L, which is responsible for the lightness in the Lab colour system and surface moisture of the samples, allows to draw a conclusion about the absence of an explicit connection between the above-mentioned processes.