Ornament can be decorative but the decorative is not ornament on it’s own. One thing that is necessary to be called ornament is a unit (ornamental unit) or what can also be called a “motif.” The unit to be manipulated can be as simple as a square or as complex as a flower.
One typically looks to precedent to find these motifs as it has all been done before, more or less. Page through Owen Jones’s the Grammar of Ornament (1856) and find the motifs of many contemporary designer’s affection.
When the unit is dismissed or abstracted to a mere object in space it becomes decoration. Objects can still move through space, just not in the same way. Thomas Beeby in an article titled, “The Grammar of Ornament/ Ornament as Grammar” distinguishes 9 ways in which an ornamental unit can be manipulated. Here they are:
Translation, Rotation, Reflection, Inversion
Translation reflective inversion
slipped reflection alternation
Acceleration, Deacceleration & Figure ground
More specific examples to follow as well as a further exploration of the idea from Kent Bloomer’s book “The nature of Ornament” that ornament works to transform an experience though the imagination to create a simultaneous occurrence between material and form and material and meaning.