Expert's Refining Stone

What it’s for

It’s the material for 40 recipes from level 15 to 25. The Expert’s Orichalcum weapons in Blacksmithing take 5 each, and the Wind Breeze and Chaser bracelets in Handicrafting take 2.

Seen in game: in the inventory it’s the green orb, the one that sits next to the grey Refining Stone. It can be sold on the Market. Check what people are asking for it there before handing it to the NPC, who only pays 160.

Where it drops

According to metabot, it always drops from the Hero bosses of Chaotic Lower Reshanta (server time):

Boss	When it spawns
Watcher Kaira	Every 3 hours from 01:00
Guardian Lord Nahma	Sundays and Fridays at 21:00
Executor Tamasa and Executor Argo	Mondays, Thursdays and Saturdays at 21:30

It can also drop from the last boss of Krao Cave, Draupnir, Urugugu Canyon, Vakron Sky Island and Ferocious Horn Den, and from the Fire Temple cubes, but not every time.