Shane Wohlers, of Aparima College School, asks :-
How and when were magnets first mass produced?
Colin Hooker, a physicist at the University of Canterbury, responded.
The first magnets were lodestones, a naturally occuring mineral of an oxide of iron called magnetite. Compass needles were first made at least 2000 years ago by stroking pieces of hard steel with a lodestone.
The production of relatively large permanent magnets in commercial quantities appears to have taken place shortly after 1730. Using a technique pioneered by Servington Savery, Gowan Knight, a librarian at the British Museum, manufactured and sold several standard types of bar magnets comprised of bundles of hard steel wires which had been magnetised by stroking them with a lodestone.
Although expensive (typically 3 weeks of a librarian's salary) they sold throughout Europe. Faraday used a Knight magnet in his experiment that led to the electric generator. Hard steel permanent magnets, magnetised by currents passed through a coil surrounding the steel, continued in use in electrical machinery until the mid-nineteenth century when they were replaced by powerful electromagnets.
It was not until after 1931 that the powerful permanent magnets based on alloys such as Alnico (aluminium, nickel, cobalt and iron) became available and replaced electromagnets in some applications such as in loud speakers and small motors. In the last few years these in turn have been replaced by even more powerful magnets based on neodymium.