Here are my 2 favorites. Colored with some tie dye solution we had left over. I filed the edges of the bottle so it's not sharp. No drainage, though, so I'll have to put gravel in the bottom.

Oh, I like those!!! I'll have to try that way of making pots.

Yes! It was pretty simple. Just use lots of mold release!!
(unless you want a glass jar in a concrete pot. ha ha)

Very clever. I make cement stepping stones and ornamental things in old jello molds and kids sand castle molds. I've been longing to do it lately, maybe i'll also mix up some hypertufa and try your method.
Kathy