Two white smoke trails, grey-blue in the shadow of the detonation products, and one black trail. To their right, the refractive images of the shocks are seen as a distortion of the natural background. From the top down are the primary shock front, the reflected shock front, the contact surface, also seen as a kink in the smoke trails, and the Mach stem shock front. The triple point, where the three shocks meet, is a little below the centre of the picture. The movement of the smoke trails and shocks is analyzed to provide the physical properties of the blast waves.