The aim of this work is the study of two black coatings: a spray of black paint, an amorphous carbon film deposited by magnetron sputtering. Our interest in such films is motivated by research on coatings with an homogeneous thickness realized at low temperature in order to characterize steels. The thermophysical properties are measured by means of lock-in photothermal thermography. An analytical study in the Hankel domain is performed, based on the study of heat transfer in the infrared sequences. For thermographic application on metals, using a thin film of carbon appears more favourable.