Before you start; you will need 4 million gp to 4.4 million to start this method of money making, maybe more.
 
First you need to start buying Tzhaar -Ket-Om (Obsidian Maul) at 100k-110k each. You will need to buy 40 of them.

Then you will need to sell ot the Tzhaar Weapon Shop at 7500 Tokkul each. Then go buy an onyx gem (uncut) form the jewels store at 300k Tokkul each.

Next, you will need to collect the items needed to make a Onyx Amulet (or Fury Amulet). Then go to a Fury crafter and  let them make it into a Fury (Players in forums do it all the time).

Sell in World 2 Falador Garden, Tree Patch

Repeat and Rinse to gain up to 1 million gp at a time!=)

~ Guide by Cheeseguy203