The reference block type 1 according to EN ISO 9934-2 (former description “MTU test block”) is used for checking and supervision of the indication sensitivity of magnetic particle crack detection agents. The surface of the residually magnetized reference block contains a network of coarse and fine cracks. After diving into or spraying with the testing ink, the crack indication is controlled and judged. The pictures show the crack indications on an reference block type 1 obtained from a yellow-green or red-orange fluorescent and from a black indication medium together with white back-ground paint. The indication sensitivity of different mixtures or charges can be judged by comparison of the indications obtained from the same reference block. Also, by periodical super-vision of the indication pattern, the use-caused reduction of the indication sensitivity can be controlled.
