Medium is steel.

Important: When used with shade use no more than 40 watts maximum
(we suggest 25 watts)
Fitted with four porcelain medium based socket
Choice of patina is rust or black iron for most products unless otherwise specified.
Choice for mica is amber, or natural silver.
We do not recommend using over 60 watt bulbs for any of the fixtures.
UL Listed for dry location
When applicable some chandeliers come with three feet of chain for a laced mount.   
Also included is a cover plate and mounting hardware.
Some of our chandelier products will require a reinforced junction box for the additional weight.
Please inquire if you have any concerns or questions about the weight appropriateness of fixtures.