I made my first leaf casting several years ago. Leaf castings are made from Play Sand, Portland Cement, Fortifier/bonding agent and water. Once the right consistency is achieved you can use any number of leaves as molds. I like to use rhubarb leaves, some are so big you can use them for bird baths. I’ve used hosta leaves, such as Sum and Substance, and begonia leaves. Once it is dry, you can paint them to your hearts content.
The one tip I have about making bigger castings is to reinforce it with wire netting of some sort. I made one that was large and I was so proud of myself, until it cracked apart. Next time I will take my own advice!