Harmony is achieved in a body of work by using similar elements throughout the work, harmony gives an uncomplicated look to a piece of artwork or sculpture. Source
A cohesive design is something that all artists strive for. There is always a method to the madness, even in abstract art, and it is truly remarkable to see a finished piece achieve the element of harmony.
It doesn't always happen, but look at how magical it is when it does! Line, shape, form, contrast and color some together in both of these pieces to create a harmonious design!
How would you best describe a piece that has achieved harmony?