The coloring materials present an important diversity regarding the contexts in which they are discovered and their physical, chemical, petrographic and mechanical characteristics. Identifying these materials provides insights into the ways ancient societies used and exploited thoses materials.Geochemical approach questioned the properties of rocks to record their history: formation, alteration, diagenesis, etc. In this perspective, few technics allows access to a precise and reproducible quantification of the chemical elements that compose the material.We propose here a step-by-step study of the geochemical composition of six European iron-rich rocks reference to understand the pitfalls of geochemical analysis and statistical processing of data.Thus, in order to undertake the analysis and processing of geochemical data on such archaeological materials, it appears essential to have references of various materials adapted to study of colouring materials: (1) to calibrate the different devices to match the physical constraints related to the analysis of iron-rich materials, (2) to understand the geological mechanisms behind the geochemical composition of materials, (3) and to compare geochemical analyses conducted on archaeological materials with geological references that are not only local but also compatible from a geological point of view. It is a question here of comparing what is comparable.