The use of natural semiconductors

I've started collecting remnants from the era of crystal radio (1900-1930) - partly to use to explain what I'm doing in performances but mostly to learn some of the lost history of this technology. There is plenty of information out there, but a lot of the practical details are missing. This is interesting to me after doing this DIY for so long, seeing how it worked when these techniques were widespread.

It was common for crystals and cats whiskers to be sold in these tiny tins (and at this time the semiconductor industry was thriving in Britain). I think there are two types of springs here, the ones on the left were used for tensioning the screw and the ones on the right are actually the cat's whiskers that touched the crystal surface. The pressure is critical in making a good point contact junction, so they would have been specially made to provide the correct resistance. I'm not sure but I think the little plastic pill containers were not contemporary as in the 1920s when these tins were made, plastic was confined to bakelite and ebonite.

This is a tin that contained a crystal of "Hertzite". There were many brand names but usually it seems these contained galena, which was considered one of the best for radio detection - as it was more 'selective' (could be tuned to only pick up the station you wanted to listen to) than other minerals. I'm not sure where the galena would have originated from but presumably being based in Gateshead maybe nearby County Durham which has lots of lead mines such as Blackdene Mine. I'm also curious as to what they used to mount crystals.

The 'perfect' crystal - interesting though that they used silver wire for the cat's whisker. Image from the excellent radiomuseum.org

Neutron were a company that was immensely popular for a few years - apparently following 16 months of R&D they developed a crystal that "doubled the range" of a radio receiver. Inside the tin we find several galena crystals, all bright and fresh - I've often wondered how long it takes for fresh galena to tarnish, it seems these have lasted well since the 1920s. Apparently the best galena was argentiferous, or silver bearing. Some of the Cornish mines also reported silver sales from galena processing.