Model animation is a form of stop motion animation designed to merge with live action footage to create the illusion of a real-world fantasy sequence.
Many types of models have been created and developed and are mainly depended on the budget of the film:
Clay Models: Unlike most clay figures used for animation, clay models have an inner metal skeleton designed to allow them realistic movements and expressions.
Build-Up Models: these type of models are more expensive and detailed than clay models. they are made by building up pieces of foam on a metal skeleton it to creat a body, and then either brushing on several layers of liquid latex on top, or casting soft rubbery skins and attaching then to the padded armature.
"Casted" Models: this type of models are the most expensive type used in the industry and are longer-lasting than the other types. these models start as clay sculptures that on top of them a 2 (or more) part mold is made in order to reproduct all the details of it. then the mold parts are assembled with an armature inside of them, and are filled with a liquid material (foam latex, silicone rubber, urethan foam, etc.) that then forms a soft rubbery "flesh" over the skeleton.
Model animation was pioneered by Willis O'Brien, and it was first used in The Lost World (1925). His work also includes
Picking up the model animation baton from O'Brien, and refining the process further, introducing color and smoother animation, was his protégé, Ray Harryhausen. Assisting O'Brien in Mighty Joe Young in 1949, Harryhausen went on to do model animation (and other special visual effects) on a series of feature-length films, such as:
The third generation of model animators featured such notables as Jim Danforth, David Allen, and Phil Tippett.