This talk develops the experimental and archaeometrical approach of Fontainebleau's engravings undertook over the last three years in the framework of a collective research program on Fontainebleau's rock art featured in this session (B. Valentin et al.). Based on a detailed knowledge of the engraved material, the present contribution evaluates the technical involvement of mesolithic hunter-gatherers into these symbolic practices by examining two dimensions. The first one is technical and concerns the scarcity of curved grooves : is that scarcity resulting from a cultural choice or a material constraint linked to the engraved sandstone or the lithic tools ? The second one is temporal with the time span to complete the main patterns (grooves and grids) which is an essential data needed to understand this vast rupestrian phenomenon.