These started out as ordinary plastic water bottles.
They were washed out, allowed to dry, had the tops cut off, and given a gesso base coat. The greenish-black one actually got a black paint base instead.
I thinned out some green acrylic and let it run down the sides of the bottle and sprayed it with rubbing alcohol, which spreads the paint out in interesting patterns and rivulets. When it was dry, it got a topcoat of varnish to seal it.
The other two got a bright floral pattern and a crackled pattern, which was achieved by painting a base coat of darker green, a thick coat of crackle medium, and finally a top layer of brighter green. All of them were trimmed on the top edge into a wavy, almost scalloped pattern. These can be used for pen/pencil/paintbrush storage, or as vases, like so :)