Chromatic parameters as performance indicators for stone cleaning techniques

To determine the degree of soiling of urban buildings subject to environmen tal pollution and, at a later stage, to assess the effectiveness of cleanin g techniques on the types of stone used in the construction of these buildi ngs, it is very useful to define the chromatic parameters (L*,a*, b*,C*,WI, and YI) before and after treatment. A comparative study of these parameter s and the original color of the stone is carried out. The best cleaning per formance is achieved using a hot waterjet at a temperature of 90 degrees C and a pressure of 120 bars. In areas with significant black encrusted gypsu m and calcite layers, these cannot be removed completely with water. Thus, chemicals must be applied the most appropriate being sodium hydroxide-based products. Using these cleaning techniques, it is possible to obtain chroma tic parameters that come close to those of the stone in its original state, allowing for an increase in yellow hues resulting from the preservation of the patina inherent to the natural aging process that stone surfaces under go. (C) 2000 John Wiley & Sons, Inc.