There are two sound holes in the bottom board, as the playing techniques of the qin employ the entire surface of the top board which is curved / humped. The inside of the top board is hollowed out to a degree. Inside the qin, there are 'nayin' 『納音』 sound absorbers, and a 'tian chu' 『天柱』 and 'di chu' 『地柱』 soundposts that connect the bottom board to the top. The boards are joined using bamboo nails. Lacquer 『漆』 from the Chinese lacquer tree ("Rhus vernicifera") is then applied to the surfaces of the qin, mixed with various types of powder, the most common being "lujiao shuang" 『鹿角霜』, the remains of deer antler after the glue has been eremoved. Often, ceramic powder is used instead of deer antler powder, but the quality is not as good. After the lacquer has dried (a qin will need several layers), the surface will be polished using oil stones. At the head end of the instrument is the "yue shan" 『岳山』 or bridge, and at the other end is the "long yin" 『龍齦』 (dragon's gums) or nut. There are 13 circular mother-of-pearl inlays which mark the harmonic positions, as well as a reference point to note position, called "hui" 『徽』 ("insignia").