Geometric platter by Warren MacKenzie. Shino with iron.  Heralds back to the earlier days of Warren and his Bauhaus training.  I have also included some images (obviously not part of the package) from Tate Museum in the UK.  The lithographs are from the 50's.   True midcentury design.  
Dimensions (Diameter X W in inches):15 X 2.5
Maker Mark: No
Stillwater Mark: No