I did another instructable where I made conchos and snaps with quarters.https://www.instructables.com/id/Handmade-Conchos-a...
The feedback was very positive, and led me to do another one with just buttons. I made buttons out of Quarters, Dimes, Nickels, and Pennies. Even new pennies, post 1960's in which there is a lot of zinc.

The key is to go slow and dome they pennies out slowly.

Step 1: Dome It Out and Add the Post

Dome it out slowly. Working from a large radius block to the smaller.

When you have it where you want it. Drop a copper rivet (michaels/tandy) into the middle. Heat with a small propane/butane torch and then attach the post to the coin with some solder. Once it is cooled, it is time to shine it with a buffer will. You can also get a buffing wheel for a dremel.

Step 2: Flatten the Rivet

In order to make a button, the post has to have a hole in it for the thread to go through. I set the rivet and coin on the edge of the vise and hit it with a hammer and flat punch. This made a nice flat area for a hole to be drilled through it.