First, the material of roof tiles.
The tiles on the roof of the Forbidden City are not like those of ordinary people. Since ancient times, royal things have been very particular and unique. Although they are not made of gold as in folklore, they shine like gold. This is actually a special kind of glazed tile, and the firing process is very complicated. The whole process needs 36 processes. After the finished product is made, the surface is very smooth and has a certain inclination, so it is difficult for anything to stay on it.
Second, the style of roof tiles
The style of glazed tiles in the Forbidden City is also very different from the square bricks we usually see. They all adopt the style of "pipe tile", just like a small cylinder, and the problem of birds is taken into account at the beginning of production, so its width is much larger than the toe spacing of all birds, which makes there is no place for birds on the roof of the Forbidden City, and birds will slide down as soon as they stand up, so there will be no bird droppings and birds without birds.
Third, clean regularly.
The Forbidden City is a solemn place. A bubble of bird droppings and a weed have affected the majesty of the royal family, so we attach great importance to health work. To this end, the royal family has special institutions and personnel to maintain health. Generally speaking, the tiles on the roof of ordinary palaces are replaced once every three to five years, and those in large palaces are replaced once every ten years.
Moreover, there are special cleaning eunuchs who regularly clean up the garbage in the Forbidden City. In that hierarchical society, no one dares to be vague, because a little negligence may lead to a bad end.
Therefore, for 600 years, the Forbidden City has maintained a golden light, and nothing grows.