Take a quite ordinary-looking powder, just add water, and 30 minutes later it begins to crystalize, and gradually hardens, and once it cures is incomparably rigid and impermeable to water.
看似平凡的粉末，加水三十分鐘後就會開始結晶，隨即慢慢凝結，一旦膠結後就堅硬無比、滴水不漏。