WO3, though at first sight simply another example of an anisotropic oxide subject to bombardment-induced amorphization, has particular importance in that the depth of the amorphization (Ra) can be estimated with great accuracy. The procedure is based on preparing anodic WO3, crystallizing it on its metal substrate at 350 or 450 °C, bombarding it, and then making direct use of the brilliant interference colors. Only Kr impact was studied, the values of Ra being found to lie in the region of 50 to 390 Å for Kr energies of 4 to 35 keV. It is argued that such values of Ra can be used to deduce [Formula: see text], the mean damage range. One postulates that the fraction of atoms initially displaced at Ra is unique but otherwise unspecified. This means that the quantity γ ≈ (Bt) exp (−ξ2/2), where Bt is the dose, ξ stands for [Formula: see text] and [Formula: see text] is the mean damage straggling, should be invariant for a given bombardment energy. In solving this equation advantage can be taken of the fact that the ratio [Formula: see text] tends to be constant (1.6 ± 0.2) for intermediate mass ratios and low energies. The result was a series of estimates of [Formula: see text] which could be shown to be closely similar to the exact Thomas–Fermi values of Winterbon.