Vicinal Si(001) surfaces with ≈4° miscut toward  consist of ordered terraces that are separated by a double step every 4 nm. Adsorption of Au at 800–900 °C changes the step morphology dramatically: after a critical Au coverage of 1/3 ML is reached, Au condenses from an initially formed lattice gas into a (5 × 3.2) reconstruction on newly formed (001) terraces. The steps of the vicinal surface are accumulated in irregular step bunches to conserve the macroscopic miscut. With increasing Au coverage the step bunches are transformed into well defined facets. The ultimate facet orientation depends on the adsorption temperature, although at temperatures above T = 800 °C only (001) terraces and (119) facets are observed. Depending on the deposition temperature, the terraces and facets exhibit a periodicity from 200 nm to 4 µm and a structural length of up to several millimetres. Illumination with white light under grazing incidence results in a colourful striped pattern in an optical microscope. A novel in situ light diffraction experiment is presented, that is perfectly matched to the mesoscopic dimensions of the faceted surfaces. Illumination with a He–Ne laser during and after deposition results in complex diffraction patterns that can be used to estimate the length of the terraces. The temperature dependence of the terrace length shows an Arrhenius behaviour with an activation energy of EA≈2.8 eV during the initial stages of the faceting; at T = 825 °C the terraces extend with a constant velocity of 30 µm s−1. This value is in excellent agreement with earlier low energy electron microscopy measurements.