Method for the identification of a homogeneous material (e.g. a liquid) in a container (e.g. a bottle) by measuring its X-ray or gamma spectrum and deriving its specific attenuation function. The method comprises building a database of the attenuation functions of empty containers, of containers filled with various fluid materials and of the contained fluid materials itself (by subtracting or devoluting the empty-container-attenuation-function from the filled-container-attenuation-function), recording the spectrum of an unknown material in a container and comparing this spectrum to the spectra in the database.