Felted Necklace

I have perchance found some felting yarn in my local yarn store and finally tried to make felted balls for a necklace. All in all, the final result turned out pretty decent. But I have to improve my skill further, because I cannot keep small cracks from appearing sometimes on the balls' surface. I got some advice on how to avoid them from a few different tutorials. Still, I am obviously doing something wrong. But as they say, practice makes perfect, so I hope my technique will become better in the next project or two.