I believe there's a bug in the first line of your code:

Mercury, lead and tin were not really used a lot to make weapons.
Weapons might not be real household appliances, but they do kill :)
Iron and Copper (Bronze) however were used a lot for weapons.
[download]

I ran your source through the debugger and it reported:

Bronze is typically 88% copper and 12% tin

Therefore if Copper was used a lot in Bronze weapons, then Tin was also used around 1 / 7.33333333333333rd of a lot, which is still rather a lot.

If it wasn't for all that Tin then Bronze wouldn't have been used for those weapons... and Cornwall wouldn't have had such a thriving export trade in ancient times!