Boss, I'm new here but have been around for three years.I'm from Mich also...Mt. Clemens area. Known before as Digger_Beginner.
Back to the green...If a coins not valuable I experiment to get them to look as shiny as I can. If it's a pretty patina I leave it alone.
A SURE CLEAN METHOD is, (my invented mixture I might add)..

...MIXING 50/50 HYDROGEN PEROXIDE AND LEMON JUICE ... (this will clean even the most fertilizer eaten zinc pennies!)....DO NOT MIX silver and copper coins, SILVER WILL TURN COLOR OF COPPER, BUT by soaking them alone in a freash amount they will turn back. THIS WORKS VERY FAST and the mixture will turn green within ten minutes.
....MIXING 25/75 IS LESS DEVASTATING...this will also PULL MOST STAINS OUT of coins!!!
This 25/75 MIX is a great mix when you just get home with your CRUDDY FINDS, throw them in this mix, go get cleaned up, grab something to eat, clean-up then rinse off your finds, sit down with a towel and magnifying glass and enjoy.(ALL CRUD should be off)
MORE STUBBORN COINS...leave in longer or increase the hydrogen peroxide. (no need to heat this mixture!)
THIS WILL LEAVE A DULL SURFACE FINISH ON THE COINS, SO...i use a ...BRASS BRUSH... to bring back the shine. The brass is softer than the coins so it DOES NOT scratch them. JUST TO BE ON THE SAFE SIDE, I would not use this brush on valuable coins or soak valuable coins in any acidic solution without constant monitoring. ....a brass barbecue brush and scraper is perfect because it has a 2" x 3" brush on a long wood handle which can be laid flat on the table and is stable enough where all you need to use is one hand to push down and rub the coin.
I hope this helps.......I also like the other guys idea on using the "NEVER DULL"(excellent for brass finds but works well on everthing but you NEED TO GET THE CRUD OFF FIRST)....This might work after the soaking and used in place of the brass brush.
***NOTE..IMPORTANT*** COINS MUST NOT LAY ON TOP OF ONE ANOTHER AND SOMETIMES COINS MAY CLEAN MORE EVEN IF TURNED OVER AT TIMES.
TAKE CARE, JOHN