Most of these records were made of a simple sheet of fairly thin printed cardboard with a very thin plastic coating and their audio quality was substandard. Some were more sturdy and well-made and they equaled or actually surpassed the audio quality of ordinary records, which were still made of a gritty shellac compound that introduced a lot of background noise. In 1933, RCA Victor in the U.S. issued a few typical cardboard-based picture records but was unhappy with their quality and soon began making an improved type. A rigid blank shellac core disc was sandwiched between two illustrated sheets and each side was then topped with a substantial layer of high-quality clear plastic into which the recording was pressed. Like nearly all records being made for the general public, they were recorded at 78 rpm, but one issue was recorded at 33⅓ rpm, a speed already in use for special purposes which Victor was then unsuccessfully attempting to introduce into home use. It was the first 33⅓ rpm picture disc and the only one made until many years later. These were deluxe picture discs, priced much higher than ordinary records, and they sold in very small numbers. In the early 1930s the entire record industry was being devastated by a worldwide economic depression and the proliferation of the new medium of radio, which made a wide variety of music available free of charge. Picture discs of all kinds were among the casualties.