We propose two approaches to artistic (non - photorealistic) rendering of functionally defined volumetric objects. The overall object shape is modeled as a group of implicit primitives. The internal density of object is defined with special Noise or Turbulence functions. For rendering purposes, the object defined by real functions is converted into volume data. An artistic image is generated by using the density value obtained from the volume data. The proposed method makes it possible to create cartoon images and animations of steam or smoke, which are volumetric objects without clear boundaries.