First I laid large leaves face-down in soft soil (technically you're supposed to use sand) so that the most pronounced leaf-veins were facing up. Then I bermed the soil up around the edges, about two inches high, creating a mould in which to pour concrete.
I used one whole bag of Sacrete concrete mix, meant for projects of 2" thickness, for this batch of experiments.
In the largest (rhubarb) leaf, I poured about an inch of concrete into the mould, then pressed a leaf-shaped cut-out of mosquito netting into the surface and poured the last inch in. This step was possibly pointless, but I didn't have chicken wire handy, which in my mind would have helped strengthen the set concrete (like rebar). I should probably Google these things like normal people, but sometimes I forget that Google exists, which is odd.
This next one is a squash leaf, which is more stubbornly clinging to the set concrete, so I'll have to wait until it dries and crumbles off before I can really see the imprint.
The last experiment is a hosta leaf, which broke because I accidently added too much water to my second concrete mix, making it too soupy. I hastily dipped the soupy surface off and poured it over a hosta leaf. The mix was too much of a slurry to be strong, but the vein-imprint is still very cool.
So all of this is in preparation to finish Bev's fountain, which has a large concrete Gunnera leaf as the waterfall feature. We are going to make 'stepping stones'/'facing stones' in actual pan-moulds so they are a uniform thickness. We'll either do leaf imprints (putting leaves in the bottom of the pans) or set black stones into the surface in swirling patterns, depending on how the spirit moves us :)
(...Time passes...)
...Here are the concrete leaves, holding the edge of the garden bed next to the entrance pathway..