Just picked this up on pinside and thought it looked like fun. Its a method of copper coating your balls. See the attached picture for the comparison shot

So heres the method.
Take a mug and half fill it with vinegar (distilled or malt, either works)
Add some salt (around 2tsp)
add around 1tsp of sugar.
dissolve the slat and sugar in the vinegar.
Find about 10 pennies or 2p's. The older and mankier the better.
Lob them in the cup and swirl a bit.
Leave for 10 mins.
Check the pennies. If they;re shiny remove them.
Throw a couple of pinballs in the cup. Swirl them every minute or so.
After 10 minutes you;ll have copper coated pinballs.

So heres the method.
Take a mug and half fill it with vinegar (distilled or malt, either works)
Add some salt (around 2tsp)
add around 1tsp of sugar.
dissolve the slat and sugar in the vinegar.
Find about 10 pennies or 2p's. The older and mankier the better.
Lob them in the cup and swirl a bit.
Leave for 10 mins.
Check the pennies. If they;re shiny remove them.
Throw a couple of pinballs in the cup. Swirl them every minute or so.
After 10 minutes you;ll have copper coated pinballs.