[OXO cube]

hi Leo 

from an internet search 

''Anodising is an electrochemical process which converts a metal surface into a durable, decorative, and highly corrosion-resistant anodic oxide finish. An electric current passing through the metal part immersed in an electrolyte solution creates the anodic oxide surface.''

Materials that can be anodised include

• Aluminium and its alloys are the most common materials to be anodised.
  
  
• Steel
  
  
• Hafnium
  
  
• Zinc
  
  
• Titanium
  
  
• Magnesium. 
  

therefore it would be a very safe bet to conclude that it is metal 
hope this helps 

Kev