Examples of Heterogeneous Materials, including plated, painted dirty, “buried” or mixed substances. XRF spectrometry is generally considered a “surface” analysis. However, X-Rays can penetrate the surface to some extent, depending on the nature of the material. Light elements (e.g., C,H,N,O) are weak absorbers of the radiation and allow for deeper penetration of X-Rays compared to transition metals and elements with higher atomic numbers. If a material is not homogeneous (and if the analysis is being carried out non-destructively on an item), the XRF result will be a weighted average of the composition of the surface and interior. Similar averaging is seen for particles or components that are placed in a side-by-side arrangement. Some examples are shown below.