The behavior of copper and aluminum slabs under tension, resulting from the detonation of a slab of explosive in contact with them, was studied. A new technique, based on microwave interferometry, was employed for continuous observation of the free‐surface velocity. Retrieved metal discs were scanned for microfractures. Tensile stresses, especially in regions where no observable damage occurred, were studied. They were found to be significantly lower than the negative pressures calculated by the common codes, already at early times of tension. This discrepancy increases in a gradual fashion with increased duration of tension. Observable damage appears only after a considerable reduction in the tensile stresses has already taken place. Elastic behavior of copper was studied by observing successive shock wave reverberations in the metal.