How were the more subtle off metal errors verified before XRFs and digital scales?

[TR137]

I'm familiar with XRF and specific gravity testing, and ping testing, but was wondering what the error coin market was like decades ago before TPGs. Was a coin sounding off when pinged enough to make it a valuable mint error? Was there even a market for such oddities? How did they establish the exact metallurgic content non-destructively, or was it practice to file off some of the edge and do chemical tests on the filings? Was there some clever way to do specific gravity testing without a 0.001g digital scale?

[Zimmy]

I started collecting errors over 40 years ago. The main variables I used to determine wrong planchets/off metals were weight, color, thickness and diameter. I also used tables to determine wrong stock errors. I don't remember much about orphan off metals/wrong planchets. Filing edges was a practice that occurred years before I got involved. My guess was prior to the 70's.

[TR137]

I started collecting errors over 40 years ago. The main variables I used to determine wrong planchets/off metals were weight, color, thickness and diameter. I also used tables to determine wrong stock errors. I don't remember much about orphan off metals/wrong planchets. Filing edges was a practice that occurred years before I got involved. My guess was prior to the 70's.

I'm not about to start filing edges, don't worry. Were you measuring thickness on the rim, the center, or field to field?