First of all, use one cup of cool water to dissolve one cup of starch, remember to stir immediately after the water is poured into the starch until it is stirred well, otherwise the starch will be easily deposited. Then pour four cups of water into the pot, wait until the water boils, put a small amount of alum in the water, a little is enough. After adding the alum into the boiling water, immediately pour the water starch into the pot, the ratio of starch to water is exactly 1:5. Keep stirring the starch with a spatula, otherwise it will easily stick to the pot. When the starch in the pot becomes sticky, you can turn off the heat. Then pour them into the prepared container to cool.