The dimo

The dimo is an integral part of shaping the tone of the dizi; in fact, it is what gives the dizi its harmonics-rich timbre. The best kind of dimo tends to be lightly translucent and consistent in fibre pattern (straight lines running parallel) and be thin enough without being completely fragile.

good dimo vs less good dimo
Comparison of a higher quality dimo (on left) versus a lower quality one (on right).

The dimo can be adhered to the dizi either using saliva (not recommended except in an emergency), or with ajiao (阿胶)/ejiao, a type of donkey-hide gelatin. Peach sap and finely crushed garlic juice are also alternative means of sticking the dimo on the dizi, but are not really recommended. The adhesive should be applied around the mokong thinly while avoiding getting any inside the mokong. Note also that other forms of adhesive like paper glue or white glue should not be used.

ajiao/ejiao
Modern day packing of ajiao (阿胶). Despite the small size, one such piece can last for years.

Prior to applying the dimo, it can be crumpled a bit to relax the fibres a little to make it easier to apply while maintaining several horizontal creases. The dimo's fibres should align with that of the dizi, so that the creases are perpendicular to it all.

good dimo application vs bad
Comparison of a well-applied dimo versus a not so well-applied one.

A properly applied dimo will be loose enough that the lowest and highest [normally] playable notes (usually the for tongyin as ) are easy to play, while not so tight that the timbre sounds bland. There ought to be a light buzzing sound accompanying the resonances of the dizi. A short term way of obtaining this timbre from an applied dimo is to press gently on the dimo with the ring finger to loosen it a little before immediately playing it.

It is often easier to start with a tighter dimo and trying to loosen it than the other way around. To obtain the buzzing timbre from the dimo more permanently, some water around the dimo adhered to the dizi can be added with the dizi gently played. Eventually, the water will evaporate off, and the dimo will retain the correct tension.

The dimo tends to lose tension in warmer areas and gain tension in cooler areas. It is often necessary to counteract these with the technique discussed earlier, i.e. get enough tension so the notes can be played before trying to loosen the tension with the technique.