What belongs in a museum?

The second level Archaeology skill "It Belongs In A Museum" reads:

Send an artifact to the giant, secret scary government room full of boxes, and gain experience equal to its value.

but I can't seem to do anything with it. I've tried using the spell on anything that would seem to be an artifact and most things that wouldn't: monuments with flavor text, any items I've found, monsters, etc. but nothing happens.

So what constitutes an artifact?

By "artefact" it's referring to items that you pick up and put in your inventory (or use) - specifically this is any specially named weapon, ring, armour, shield and so on.

The same applies to the next Archaeology skill, "This Translation is All Wrong!", which will convert an artefact (and thus all it's stats, etc) in to another artefact of the same type and star-level (with brand new stats).

To use the spell you first equip it as per usual and then just right-click an artefact that is in your inventory, if it works the game will ask if you wish to send it or now.

If you need an artefact to test, the most reliable place to get them is from completing an inconsequential side quest.