Further to your earlier articles about materials used for making medals I attach an image of a large medal (146mm) recently acquired. It is of Prince Louis Napoleon, better known as the Prince Imperial. I am still researching Spence's Metal but have determined that

1) It was invented by a Mr Spence of Manchester,

2) It was described as "new" in 1880 and

3) It was not a metal! It was, in fact, a mixture of metal sulphides dissolved in sulphur.

It had the useful properties of a low melting point (a little over 300 degrees Fahrenheit), expanding on cooling, and high resistance to acids (including aqua regia). It was primarily used for sealing joints in iron pipes and I haven't found any references to its use for making medals.

The Prince Imperial (son of exiled Napoleon III of France) was killed in 1879 while serving with the British army in South Africa, so this medal could commemorate that event or be advertising a new product - an International Inventions Exhibition was held in London in 1885.