I found some clay that I like a lot and it's made in Nixa Mo. I had asked about reinforcement in clay and this was recommended, it is very smooth working but has chunks, what they call, tooth and grog. Here are 1 2 and 3 with this clay. Oval land water and a 16" long kidney. Here is a close up of the toothy, groggy, chunkyness.
J.B.pines are in concrete pots over 20 years, no problems. To cure, they are left in water for about 4 weeks or so. After three changes of water, mosquitoes start to breed and you are good to go.
For a little while I considered setting up a salt water reef aquarium and did a lot of research on making concrete live rock. The rock would be cured in fresh water over the course of several months with weekly water changes. For small amounts the rock they could be placed in your toilet tank. Another was to find a creak or pond and put them there for a few months.