Just wanted to share a photo of the Fountain I made using Rhurbarb leaves.

I used 2 different size Rhubarb Leaves, but they need to be large.
You will need a large table, large pieces of plastic. Play sand I am not sure how much, but a large bag. Place the plastic bag flat on the table. Take the sand and form it making a dome. It will need to be enough for the leaf to cover. Sand should be heaved up in the center.
Place the leaf over the sand, leaf should be out to the edge of the sand. Place leaf so that you are looking at the veins. Vein side up. If you tear it you can patch with another leaf. You will notice in the center of my picture Ii have an indention in mine. You don't have to do this step but I made these as butterfly puddler's and this held the sand. If you want to do this step I used a small round plastic butterbowl, and cut a round hole in the leaf towards the top of the leaf, and pressed the bowl into the sand to form the indention. Make sure you cut the leaf to fit the bowl only, and no more.
You will need a 40 lb the bag of concrete mix. Do not use with stone in it. Mix the concrete mix, should look like thick cookie dough . Start placing on the leaf, placing and pressing as you go. Follow the pattern of the leaf. When you are done cover with plastic and allow to cure for several days. When it is dry turn over and start to remove the leaf, pulling out the vein. I found by washing down with the hose it made the job easier. You can now paint using outdoor acrylic paint. You can purchase at craft stores. I used green and red. Started with the green and than added red. I did water the paint down to get it to flow across the leaves and go into the veins. Keep doing this until you reach desired color.
. My husband built the frame using plastic plumbing pipe, and the holes for the pump water lines he used by drilling into the leaf with a stone drill bit. Do this step after your frame is set up so you can see just where you want them to go.
I made many of these leaves including with other nicely shaped large leaves. You may want to try this first on smaller leaves just for the practice. Hope this helps enjoy your project.