There is some good ideas on here, many have their favorite was and I may try some of them.
First separate the copper and the clad as they should not be tumble together or you will get red coins. Now my way is depending on the tumbler and how much you have to do, add the coins in the tumbler so its about 1/3 of the basket and a good 1/3 with the gravel and add a good squirt of lemon juice, mabe about 1/4 of cup add water until its about a half to 3/4 full, seal it and tumble copper for around hour and a half, now clad tumble for a good 3 hours or so, rinse and take out the ones that are nice and put the others that are not too good back in with some more clad and tumble again, when you drain them to that again. . most coppers only need one tumble and some I have to run again.
Now this is my method with the clad dont come out nice is I use my small tumbler and will put the coins in and add some muriatic acid, but very little and be careful with it, then add my gravel and only tumble about 1/2 hour or so and then take the coins and gravel out and rinse it well, do this a quick as possible and put them back in the tumbler and add lemon juice again to clean off the acid. if you leave then out after the acid and not rinse it seem like they will turn flat gray.
My Gravel is aquarium gravel and have so small stainless steel grit in with the aquarium gravel. the lemon juice is called real lemon and buy it from Sams as I get 2 quarts of it for around $6 or so. My tumblers are my 25 pound rock tumbler and a 7 pound for small batches. I also have a big vibrating tumbler that I use for my wheaties as they look so good and not over clean.
One of the guy uses a cement mixer with broken glass that is the stuff that shatter good, like the stuff rear car window are made of. He can do $500 of clad at one time, but I feel it is passable but not as nice as what i tumble.
If I can find the pictures as they were on my old computer andI had the files switched and some didnt switch and may post them when I find them if I have them yet.
Rick