Untreated cotton rope is great to use for perches. It can be tossed in the washing machine for cleaning. Monitor it closely so the bird does not eat any of the strings or catch a toe in a frayed area.
Perch placement: When placing perches, locate one by the food and water dishes, one by the toys, and the concrete perch elsewhere in the cage for grooming. Place the perches so they do not inhibit bird movement or cause damage to the feathers as the bird moves around the cage. Perches should be placed so the bird's tail will not touch the side of the cage when the bird is sitting on the perch. Avoid placing perches directly over food and water dishes.