Purchase a silicon mold kit from an arts and crafts store. Inside, you will find two containers labeled "Part A" and "Part B." Take out equal amounts of each part and knead them together to form a ball.

The silicon will set quickly, so have your desired button or cabochon ready. You will need one to make an imprint.
 Use your fingers to press the silicon around the sides of the button or cabochon for a tight fit. Be careful not to cover up the back. Work quickly as the silicon will start to set fast., In most cases, the silicon will harden and turn a darker color. It will still be somewhat flexible and rubbery. Once the silicon sets and you can't "shape" it anymore, pull the button out. You should now have a perfect cast., Knead some clay to soften it up first. Next, roll it into a ball, then press it into the mold. Use your fingers to press all along the back so that every crevice gets filled. The back of button should be flush with the mold.Leave the clay in the mold for now.

There may be some excess clay sticking out of the mold. Run a thin blade across the back of the mold to cut the excess clay off.
Clay should not stick to silicon, but if you are worried about this, mist some water into the mold first.
 Choose a large jump ring, then press it halfway into the button. You can use a round jump ring or an oval one. The color of the jump ring does not matter, but an unpainted one will probably hold up to baking the best.

If you can't find a jump ring, you can glue a button shank to the back of the clay piece after you bake it.
 When you pushed the jump ring in, you may have noticed a small slit in the clay. Use a pointy tool, such as a toothpick, pen, or knitting needle to smooth the slit shut. Don't worry if you end up with a slight groove. This groove will actually make it easier to sew the button on., Pick the mold up and hold it in both hands. Bend it back, like snapping a stick. You should see the sides of the button coming away from the mold. Rotate the mold, and bend it again. Keep doing this until the button is loose. Flip the mold over, and let the button fall out.

You must remove the clay from the mold. Do not bake the button in the mold.
At the point, you can make more buttons using the same mold.
 Preheat your oven to the temperature specified on the clay's label. Once the oven reaches the correct temperature, place the baking sheet inside. Let the button bake for the time specified on the label.

Each brand of clay is different. Follow the instructions on the label closely.
 If you'd like, you can paint the buttons with acrylic paint. You can also glaze them with acrylic sealer or polymer clay glaze. Let the paint and/or glaze dry completely before you use the buttons.

Consider adding the paint just to the raised edges of the button for an interesting design.
If you didn't add a jump ring, buy a button cover kit from the fabric store. Take a shank backing (a flat disk with a wire loop), and super glue it to the back of your button.
Prepare your silicon mold.
Press the button or cabochon into the silicon.
Remove the button or cabochon from the mold once the silicon sets.
Press your clay into the mold.
Push a jump ring into the back of the button.
Smooth the slit under the jump ring shut.
Remove the clay from the mold.
Bake the button on a foil-lined baking sheet.
Allow the buttons to cool before using them.
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