Just use white portland cement and sand...1 part cement to 3 parts sand...and add a couple of cap fulls of concrete acrylic fortifier (Quikrete makes one). You want the mixture thick enough so it doesn't run off the leaf.
The aprons were not an auction item, but something I thought would be fun for us to wear as we demonstrate our projects at the garden party this coming Sunday. The other demo is making ceramic pots...hands on for members...that the leader will take back to her studio to fire!
The kicker is the weather. I think it was 106 for us yesterday up at the lake. It'll probably be at least 100 here the afternoon of the garden party (4-6)....