What is the seasoning "Shuangshui" (Cantonese pronunciation) in jiaozi?

Guishui is a common traditional auxiliary material of Cantonese pastry. It is an alkaline solution with a PH of 12.6, which was obtained by boiling plant ash with water for one day and taking the supernatant. The main components of plant ash are potassium carbonate and sodium carbonate. In the absence of modern chemical alkali in history, the plant alkali prepared by this indigenous method has to be used.