We study a Au (25 nm)/Cr (10 nm) bilayer system as a model of mirror for the soft X‐ray energy range. The Au and Cr thin films are a few nanometer thick and are deposited on a float glass substrate. The sample is characterized by using 3 complementary techniques: soft X‐ray reflectivity, glow discharge optical emission spectrometry (GDOES), and time‐of‐flight secondary ion mass spectroscopy (ToF‐SIMS). Soft X‐ray reflectivity provides information about the thickness and roughness of the different layers, while GDOES is used to obtain the elemental depth profile of the stack and ToF‐SIMS to obtain the elemental and chemical depth profiles. GDOES and ToF‐SIMS have both a nanometer depth resolution. A coherent description of the bilayer stack is obtained through the combination of these techniques. It consists in 5 layers namely a surface contamination layer, a principal gold layer, a Au‐Cr mixed layer, a Cr layer, and another contamination layer at the top of the substrate.