The spatter sieve is a tool for spattering paint with a stencil brush. For example, "spat a leaf, i.e. place a plant leaf on a paper and then sprinkle watercolor on it through a metal mesh (spatter sieve); afterwards, the shape of the leaf has remained white and the paper around it is finely speckled." (1)
It consists of a small (approx. 13 by 8 cm) metal sieve (mesh width approx. 1 mm) with a short (approx. 5 cm) metal wire handle. [MOT]
(1) Dictionnary V.D. (Van Dale)