Possible Clues:

• On the outside it's valuable, but inside it's 30 across (6)
• Seems dead inside, but it's only on the surface
• Word with gold or silver
• Only on the outside, dead in the inside
• Thinly coated with deposited metal
• Covered, as with metal
• Coated with a thin layer of metal
• Dead inside, but it's all only on the outside
• Given a metal coating
• Like some silverware