The nest built by Jin Siyan for the first time is called Bai Yan, which is bright and clean in color, white or yellowish, transparent, thick and full, with little hairiness, small and thin roots (the side close to the rock wall is called Yan Gen), which swells when it rises, is slightly fragrant and has the best quality. It was listed as a tribute in ancient times, so it was also called "Yan Guan" and "Gong Yan".
If the first nest is taken away, Jin Siyan will make a second nest to shelter and hatch. This nest is called Mao Yan. At this time, due to the consumption of saliva, Jin Siyan had to mix semi-digested food and saliva with her fluff to build a nest, so Mao Yan contained more impurities, and its color was dark and miscellaneous, with poor quality.
If the golden swallow loses its nest for the second time, it will try to build it for the third time. At this time, its saliva is almost exhausted, and the gums spit out are bloodshot, dyeing the nest red, so the third nest is called blood swallow. Blood swallows are sandwiched with fluff and hair stalks, with thin walls and the worst quality.