English: Crystals of galena sold for use in Polish crystal radio receivers probably in the 1930s. They were used in cat's whisker detectors, an antique electronic component used in crystal radios, which remained in use in Eastern Europe into the 1950s. In a cat's whisker detector, the face of the crystal was touched by a fine wire, forming a point-contact semiconductor diode, which rectified the radio waves in the receiver to extract the audio signal from the radio frequency carrier wave. The crystals varied in their effectiveness, so several crystals often had to be tried to find a sensitive one. The text on the box says: "'Ramona' Gold" "World's most powerful radio crystal" "Polish Radio Industry S.F.W."