If you can, find some older ones, they're more representative of the material we use:
The alloy remained 95 percent copper and 5 percent zinc until 1982, when the composition was changed to 97.5 percent zinc and 2.5 percent copper (copper-plated zinc). Cents of both compositions appeared in that year.
http://www.usmint.gov/about_the_mint...ion=fun_facts2

EDIT: I didn't even think about what RIT would do to copper, but it's definitely a valid concern if the internals of the tubes get dyed.