The jeweller’s monocle is a type of eyewear that identifies gems. While equipped, any gem viewed in the pick up window will be identified. Gems already in your inventory must be dropped and picked up again. It also causes the blindness effect while equipped.
The jeweller’s monocle appears as a gold monocle when unidentified. The gnomish jeweller carries this item. Rarely it can be found in the dungeon too.
Cursed monocles bear the risk of permanent blindness if you have no means of taking them off.
If you kill the gnome king the jeweller from the gnomish jewellery store will arrive, attack you, and demand some money to stop attacking you. He is carrying the item. (version 1.2) If your pet kills the king, however, he doesn't show up. This needs verification because it was reported only once.
(just killed the king and he did not attack at all. 1.3)