Backstory: I've seen a surge of artists using bottles, bottle caps, pallets and other typically recycled or discarded items.
The Idea: A marketplace for artists to find and request raw materials.
Deep Dive: You would build a marketplace where artists can post request for items such as bottles or caps and what they're willing to pay or barter.
You would also allow users to post items they have/collect.
Validation: I was chatting with a local artist at a local show and they posted on a facebook group and offered to pay 2 cents for every bottle cap. The artist crowd sourced enough to complete all his projects.
Monetization: You may only be able to run ads on this platform, it's a small and inexpensive item being traded.