When the BBC was formed in 1922 the first popular wireless receiver was the crystal set, because of its relative cheapness.
Many built their own to reduce costs even further and
wireless firms tried to attract customers into buying their crystals with all means of technical inducements, one claiming that their crystal came from the Ural mountains.
As an exercise I took a typical wireless magazine of the times, “Popular Wireless Weekly,” dated July 1924. Within its but 30 pages were all these adverts for crystals.