A highly modular Dupe Plugin Adds the /dupe command to your server.
Duplicating a diamond.
You can block an exact item, all items that are of a material (e.g., Diamond, Iron Sword), or an item with a specific NBT {dupenotallowed:true}
A Blocklist Menu to guide you on blocking items. /dupeplus blocklist
Access the blocked/allowed items list in-game using the Blocklist Menu. /dupeplus blocklist