A little heads-up. I suggest using an old, worn-out bath towel instead of a plush, thick, new one. You want something with a coarse, open weave so the concrete has something to cling to. If you use a plush fabric, the water from the slurry soaks in but not the concrete, giving poor results. I've never tried it, but I'd bet burlap would really work well.
In all honesty, the towel will not supply any strength to the pot, it will be likely to crack in half when moved around. Instead of cloth, fiberglass mesh from auto repair or boat repair kit, or wire mesh would add strength. Mold the wire mesh like you would the old towel. the result can be quite similar, freeform and will have more strength.
Any time the walls of the pot are less than 4 inches (10 cm) this is considered a thin application for concrete, and reinforcement to prevent flexing when moving the pot around is critical. It is okay to try to build thinner walls, you simply must include reinforcement. Wire mesh, and fiber glass are proven materials. Organic fibers, like burlap, towels, newspaper, etc stretch when pulled. Wire and fiber glass resist stretching.
Fibers,, sold specifically to blend into concrete look like little plastic bow ties or plastic '' I - beams" but are less than an inch in over all length. Unfortunately they come in huge bags, and as a hobby pot maker you would only use a few handfuls per 100 pound of concrete mix or mortar mix. If you only use sand and cement, it is a mortar mix, Concrete is sand, gravel and cement paste.
After the project has set a week, any of the plastic fibers that protrude from the surface can be sanded off with sand paper, or sand blasted off the surface.
