Theming Bonus?

To all:
I'm not understanding theming bonus. I have the Hermitage in Jarkata and have filled it with 3 different items from 3 different civilizations and from three different eras. Beads-indonesia-Ancient, Pendant-Polynesia-Medieval, and Amulet-Brazil-Classical, and still a zero bonus. What am I doing wrong?

Thanks for the help,
vriesea

Be aware about difference between Art and Artifact.

You listed Artifacts!

Best regards...

Exactly as Taurus said. You need Art (such as "The Blue Boy") rather than beads and pendants.