They were a mixture from 1982 back. in 1982 they switched to copper coated zinc about halfway throught the year so there are both types made in 1982 and make 7 different types. but ever since then weve had coated pennies which are lighter and can be stripped. many high schools do it as experiments right beside making a penny look silver using magnesium sulhate. it does not tone the coin per say but it does change the color and it is very obvious when it is done. ive seen about 500 pennies that were played with by high school students as I was one of them. you can strip them and turn them silver colored. if it is stripped then you should beable to see a light hint of copper in a spot some where. there maybe some proffessional that can make it look perfect but none ive ever seen or heard of. Id say coppercoins would be the main person to ask here. as from what ive seen hes a copper expert. I'm eager to see what he has to say.