The Diamond Glass Hand is an item that can be sold to the Museum for 500,000 Coins. It can be made with Level 80 Crafting with 20 Glass and a Diamond. Because a Diamond can be sold the NPC Shop for 100,000 coins, which is also the Minimum Price on the Player Market, you can gain a one-time additional 400,000 Coins from the Diamond by making the Diamond Glass Hand.
After adding the Diamond Glass Hand to the Museum, it can be examined to show the following message:
The hand shines brightly as you observe it from different angles.