Can I use just two sheets of tissue paper?

You can, it just won't be as flexible when you fold it. I'd recommend not adding stems, as that will put more weight on your flowers.

Copper sheets previously used in solar cells can be melted down and stripped of impurities, to form high-grade copper as a product, but this would require lab equipment.

Yes, you can use any paper that is easy to handle (printer paper, construction paper, etc.). But make sure that the paper is a square and has equal sides (unless...

Tissue paper is a soft, thin paper usually sold in craft stores and stores that sell gifts.