Test 1 - 5 coins I totally botched the test. No scans before, hence no comparison possible after. NO RESULTS. Test 2 - 5 coins I botched 80% (4 out of 5) of the test. Therefore only one "before and after" comparison possible. Here it is: Obviously the white spots were "changed". But what disturbs me the most at this time is that the dark areas were lightened -- considerable. Pure Guess: The dark areas were only mildly affected over time (75-80 years), but my treatment resulted in a light coating of ZnO. I've got more zinc coins to fuss with so this is not over. I just need tighter standards for my process. My college chemistry classes were about 55 years ago. I've forgotten about careful control and recording of my testing parameters. At least I'm not going anywhere thanks to COVID-19.
Oh white vinegar is going to make stuff whiter. Nickel, zinc, etc. You may have to dilute it to 2% and reduce the time as you mentioned.
