Solid Drawing is a process that adds depth, height, and weight to make the 2D drawing more realistic, which overall makes the drawing have 3D effects within a 2D drawing. With the usage of balance, depth, and volume, it adds more of a third dimensional figure within the animation. 

Solid drawing grants the artist the advantage to draw the character or object with the aspects of weight, volume, balance, anatomy, lighting, shading and shadow effects and gradients.