Throwing is wet, and the water goes onto your lap. A pottery apron is not about keeping clean so much as about staying dry, which is why the material matters more than the pockets and why an ordinary cooking apron is not much use at a wheel.
What the job actually is
Slip and water come off the spinning wheel and land across the front of your thighs and lower body. A cotton apron soaks it up and holds it against you for the rest of the session. What is needed is something that sheds water rather than absorbs it, and that covers the lap when you are seated rather than only the chest.
Materials
Coated canvas, waxed cotton and rubberised fabrics all shed water and survive being washed constantly. Plain cotton does not. Denim is better than cotton and still wets through eventually. The test is simple: hold it under a tap and see whether the water runs off or soaks in.
Cut and coverage
Seated coverage is what matters, so a long apron that reaches over the knees when sitting beats a short one that looks right standing up. Cross-back straps are more comfortable than a neck loop for a long session, and a waist tie stops the apron riding up when you lean into a centring.
Washing and wear
Clay comes out of most fabrics with a rinse before it dries, and dried clay in a garment makes dust when it is next moved. Rinse the apron at the sink at the end of a session rather than letting it dry stiff, which keeps both the apron and the studio in better condition.
Questions people ask about pottery apron
What should a pottery apron be made of?
Something that sheds water: coated canvas, waxed cotton or a rubberised fabric. Plain cotton soaks through.
Does length matter?
Yes. Coverage while seated is what counts, so it should reach over the knees when you are sitting at the wheel.
How do I wash it?
Rinse it before the clay dries. Dried clay in fabric makes dust when the garment is next moved.