I need to clean some tarnished brass switch plates and then to protect them so that don't oxidize.

I recall seeing Bob having refered to a method of getting the old lacquer off brass with a solution including amonia.

Can someone point me to that information

You can take old lacquer off with paint remover or lacquer thinner. If you want to keep the switch plates looking polished longer use A product from Eastwood Company called Nyalic. It will last a lot longer and will not discolor with age. www.eastwoodco.com