Interesting question. According to what I know, the vikings often raided along the Northwest coast of Europe. With the raids, they stole many valuables, including gold and silver. So with the precious metal valuables they stole, they melted and formed various types of attachments and designs on their weapons such as swords, axes, spears, etc. For example: On a sword, they might melt some gold/silver and make it into a design on the hilt of the sword.