This is the only hint I've found. Has anybody tried?
"When I got them, the CDT tweeters were severely tarnished, they looked like they were salvaged from the ocean! But with a Q-tip and some TarnX tarnish remover they look as good as new!"
http://www.audioreview.com/cat/speakers/floorstanding-speakers/gallo-acoustics/PRD_120942_1594crx.aspx
"When I got them, the CDT tweeters were severely tarnished, they looked like they were salvaged from the ocean! But with a Q-tip and some TarnX tarnish remover they look as good as new!"
http://www.audioreview.com/cat/speakers/floorstanding-speakers/gallo-acoustics/PRD_120942_1594crx.aspx