[Vintage-Audio] Scotch Audio Tape Variations

[Duane B. Fischer, W8DBF]

Hi All, 	
	
What is the 'real' difference between the seven inch reels of Scotch autio tape
#207 and #227? 		
	
I weighed each on a postal scale, as I thought the #227 felt heavier to me. The
#207 weighed 13.5 ounces and the #227 was just under 14 ounces. 	
	
Both appear to be very high quality, the #227 I am positive is commercial grade,
as it has the black/gray oxide. 
	
Additionally, what was the thinking in the 'back coating" of audio tapes? The
reddish oxide on one side and black on the other.  		
	
Thank you. 	
	
Duane W8DBF