Click the item to receive a quest from the NPC that leases it to you, and then talk to the NPC again, this should give you 1 Armour and 1 Weapon Blackstones per day.

"Velia seal", gives you 1 Armour Blackstone, and "Heidel seal" gives you 1 Weapon Blackstone per day.

Ref. (https://www.reddit.com/r/blackdesertonline/comments/49sppz/cp_adventurer_seals/)