The Best tuning coils were made of:
Pre-wound coils for crystal radios were once made; that had the right number of wounds and diameter of coated magnetic coil wire, by coil tube size; for best AM tuning for radio stations.
This is a Crystal Radio Coil that was made around 1962, when crystal radio building was popular as a regular radio; around 48 years ago.
This is a Crystal Radio Coil that was made around 1972.
In these days earlier crystal diodes were made for crystal radios; the newer built crystal diodes were made in large quantities for maybe around 11 cents each.
Crystal radio headphones used to be built for the crystal radio; then, the crystal radio earphone was used as less crystal radios began to be used.
By around maybe 1972 crystal radios were only being made for toys or hobby building, that used mass produced diodes and earphones.
Since around 1984 crystal radio building has become harder to build; because there are fewer crystal radio components that are now available.
Because; crystal radios only used radio wave energy, they can play for 400 to 600 years.