Cook the cabbage in boling water as usual, and transfer approximately 2 liters of the juice of cooking into a bowl. Add to it two teaspoon of Alum, stirr well, and while the water is still hot, pour the mixture on the wool waiting in the pan (and keep the extra liquid into a bowl, so that you can use it later for another experience) Press the balls toroughly to allow the liquid to extirpate air bulles and help the liquid penetrate into the fibres.