When copying artifacts, the safest illumination to use would be strobe
units.  The other alternative--tungsten lights (either flood lamps or
halogen lamps)--generate a tremendous amount of heat.  When used on a
copy stand the proximity to the object is usually around 2 feet away,
which--especially if it's a dark object--will make the object quite hot.
 
Christopher Bobbitt makes an excellent point about the length of time the
strobe light is actually on.  However, when strobe lights are used, some
kind of "modelling" light (a tungsten light in the same position as the
strobe) is used  in conjunction to get an idea about where the light is
falling on the object and where shadows are forming.  Since these generate
a lot of heat, they can cause a problem if used close to the object.
Ed Bridges
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American Museum of Natural History
212 769-5277 fax
212 769-5740