Contrast the mixing of colors through additive and subtractive processes, indicating a specific material or medium in which artists use each process.

Additive color mixing is the creation of a new color by a process that adds one set of wavelengths to another set of wavelengths. ... Additive color mixing is what happens when we combine physical pigments, whereas subtractive color mixing is what happens when we filter out certain wavelengths

relief sculpture - images are set against a flat background.

a coin is a good example: the inscription, the date, and the figure are slightly raised above a flat surface. the ancient egyptians sometimes carved figures into a flat surface.  

pro: they take significantly less time to make and do not require as much tools or skills as free-standing

cons: not nearly as realistic, as it is not fully 3-d, and does not have the details that a free-standing one does.

freestanding sculptures (also called  carved in the round) are not attached to any  background.   they are 3-dimensional  and fully rendered.