Protean bar

Protean bars can be won on Treasure Hunter. They can be used on an anvil to do Protean smithing, which gives experience but no items.

You use up to 60 protean bars at once in the Make-X interface, although each one takes 8 ticks (4.8 seconds) to be smithed. The amount of experience given by the bar is 2.5 times the experience from the highest-level normal metal bar you can smith. Because only 750 bars at best can be used per hour, the experience pales in comparison to most other methods. However, it is completely free provided you have the protean bars, and requires almost no input -- 60 bars take about five minutes to make.

The varrock armour will allow for faster smithing.