Ceramic ventilator or grill tiles were originally designed for the exchange of air or heat, but can be used as wall decorations.    These vintage vents have not been glazed and are in the bisque stage.   Info on vent tiles shown in last 2 photos.
5″ x 5″ 4″ x 4″ and 3″ x 3″  thickness varies
Qty = as shown
$40 – 75 each