If you're not at skill 525 yet, there's extremely profitable 25 additional points to be gained aswell!
Leatherworking skill of 500 needed
The item in question is Triple-Reinforced Mining Bag, and it can be purchased from Ayla Shadowstorm after completing the "Filling the Moonwell" quest.
It's material costs are quite heavy:
- 3 x Pristine Hide
- 15 x Volatile Earth
Note that if the materials are too expensive, you can't make gold with this method. Sometimes people can also undercut heavily. If that happens, it's better to wait until they've sold their products first.
There's lots of other patterns, recipes and schematics available from the vendors too that will make you quite a bit of gold! I will post more about these later on.