Maybe give a magnet a try! Mark Shakarjian Sent from a device you don't need to know about ------------------------------------------------------------------------------------------------------------------------------- On Apr 23, 2012, at 12:36 PM, John Dawson wrote: Hi everyone, I was wondering if anyone had tips/resources about determining whether or not a the substrate of a laquer is steel or aluminum. I have some WWII era discs and some are definitely heavier and sturdier than others. I am wondering if these are steel. John Dawson Indiana University Media Preservation Initiative