Glad to find this thread is still active and it's great to see what you all are doing with it. I was reminded of it just recently:

My 7-year-old found this same mixture in a paperback science book for kids showing them how to turn tarnished pennies all shiny.

It explains that the acetic acid in vinegar changes into hydrochloric acid when it mixes with the salt. Same as stomach acid. No mention of the lemon juice.

He drops a penny in and 10 seconds later it's shiny. I will use it on a bunch of nuts, bolts, brackets.

If it hasn't been discussed yet, one way to neutralize the acid is to rinse the parts in a mix of baking soda and water.
-Art

65 Satellite hardtop 361/4bbl console 727 2.76
67 Satellite convert 383/2bbl column 727 3.23
67 Lancia Fulvia Sport 1.3 Zagato. Alloy body, 1.3L V4 DOHC 4-spd
67 Lancia Fulvia Rallye 1.3. Alloy panel, 1.3L V4 DOHC 4-spd
71 Alfa Romeo GT Junior 1300 Zagato, 1.3L 4cyl DOHC hemi 5-spd
82 Alfa Romeo GTV6 2.5L SOHC hemi V6 5-spd transaxle
75 Maserati Bora US spec 4.9L DOHC hemi V8 5-spd ZF
77 Maserati Khamsin Euro spec 4.9L DOHC hemi V8 5-spd ZF
07 Aston Martin DB9 6.0L DOHC V12 6spd transaxle