Originally posted by Jitatha:

To get the iron, you need to be lucky when randomly digging in swamp, or kill bonemass. Longship needs iron nails.

If you are in a position to kill bonemass then you should already have all the iron you need.

Frankly I just get the iron pickaxe and shield then head to the mountains in my upgraded bronze gear and get silver before I even kill bonemass. That takes some experience in knowing where to look for silver though.