More Ashes equals more RS gold
http://acecustomclassics.com/wp-json Collecting ashes are great way to make more RS gold especially for new players. Ashes will appear when the fire runs out from the logs which the ashes will remain. These ashes are used in Herblore in order to make Serum 207 potions.
It is recommended to use Willow logs due to it being cheap or you could also use Maple logs in order to train your Firemaking skill at the same time making more RS gold although it is slightly pricey than the Willow logs.
In order to make more RS gold you need to buy a lot of Willow logs since it is cheapest than some logs. Make some fire using the logs and wait them till the fire runs out. After that collect the ashes from the ground, be sure to fill up your inventory with ashes. Once your inventory is full, you can now start selling them at the Grand Exchange.