Читать книгу Monument Future - Siegfried Siegesmund - Страница 236

Portable XRF is an elemental analysis technique, and consequently the result of the measurements of the varnish is the areal density of the element Mn. However, the conventional literature on desert varnish usually is in terms of layer thickness, because the measurement method is based on optical microscope analysis of cross sections through the varnish (Dorn 2007). Therefore, in order to make comparisons with this literature it is necessary to convert the areal density into an equivalent thickness. However, this gives a nominal or effectiveness thickness that assumes no other minerals are present. This is not directly comparable to desert varnish thicknesses, which usually contains interlayers of clay minerals (Dorn 2007), but it is useful for comparing urban varnish layers on different structures.