Painted leaves with a painted piece of paper behind them - I am verry pleased with the detail from the leaves.
After the above experiment, the backs of the leaves had color on them, so I flipped them over and ironed again. They look very dreamy to me.
I experimented with other polyester fabrics, but the shiny stuff carries the most detail. I should go troll through Joann's for other polyester fabrics that are smooth but less shiny.
Unexpected bonus: ironing oak leaves makes a nice smell.
Unexpected negative: it is the middle of freaking winter in New England - the only leaves I can find are dead oak leaves. I wonder if people would mail me leaves... you know, from warmer climes?