Continue rolling the ball, alternating dipping it in hot and then cold water. As the ball becomes denser, apply more pressure when rolling.
When you feel that the ball is felted enough, rinse it thoroughly in clean water until no more suds emerge when you squeeze it. Squeeze out the excess water.
NOTE: Perform a pinch test to see if your ball is completely felted. Use your fingertips to pinch a tiny bit of the wool fibers, and pull them away from the ball. If the fibers pull out, continue felting .
When you’re satisfied with the density of your ball, soak it in a bowl of water and white vinegar (approximately 2T vinegar to 34 oz. [1 L] of water) to neutralize the soap.
NOTE: The slight alkalinity of soap can damage wool over time. Vinegar neutralizes the soap and restores the natural pH of the wool.
Rinse the ball in clean water, and let it dry thoroughly, preferably overnight. (If you have a cat, don’t leave your felt balls where the cat can find them. You might just wake up in the morning and have to go on a ball hunt. It has happened.)
Repeat to make more felt balls. I suggest making more than you think you’ll need, so that you have a variety of size and color options .