Sueiro Bal Marcos wrote:

 > Identification
 > The standard way to identify the base material of a lacquer disc is 
to examine
 > the disc's center hole where silver metal (from an aluminum base), 
glass, or
 > cardboard will be visible.

I've mentioned it here earlier, but glass base AudioDiscs had a 2-inch 
fibre center inside a glass base with a 2-inch hole.  Therefore if you 
look at the four holes you will see orange-brown fibre (like cardboard), 
not glass.  And to make it more confusing, sometimes there will be gray 
coating the center hole from the rubbing of the fibre center hole 
against the center spindle.  You (or was it Mike Casey) have also 
forgotten to mention the use of steel as a metal base during WW II.

 > These bases also have distinctive sounds when the disc is struck 
gently against 
 > its edge using an object such as a ring.   An aluminum base yields a 
sound that
 > has been  described as a "pong" while the glass sound is more of a 
"ping."

Or "CRACK".  Followed by the sound of swearing.

 > Cardboard will, of  course, have no sound.
 > Casey, Mike. "FACET, The Field Audio Collection Evaluation Tool: 
Format Characteristics
 >  and Preservation Problems, Version 1.0". Bloomington: Indiana 
University, 2007.
 > Marcos Sueiro Bal

If a cardboard disc falls in a forest and there is nobody there to hear 
it, does it make a sound?

Mike Biel  [log in to unmask]