Two terms describe the dimensionality of elements in jewelry: shape and form. Shape refers to the outline of a flat, two-dimensional area; form refers to the volume of space occupied by three-dimensional objects.
In reality, most “shapes” in jewelry design—sheet, stones, metal clay, flat found objects–are really “forms” because they exist in three dimensions: in addition to length and width, they do have some thickness. The same is true of patches of enamel that may appear flat, but which may actually have thickness built up layer by layer. But conventionally, unless the thickness is significant, the outlines of these forms are referred to as “shapes.”
This isn’t really hair splitting. Shapes and forms each have their own purposes, uses, language, and effect on design. Even so, they do not stand alone, each in their own universes. Shapes and forms intersect and overlap each other, and overlap other elements of design. For example, forms seen from one side may look like two-dimensional shapes. The edges of shapes and the outlines of forms can both be seen as lines that direct the eye around a piece or connect one area of a piece to another. We separate these concepts apart only to make them easier to talk about.
Shapes generally fall into two categories. They may be geometric, composed of angles and flat sides (triangles, squares, rectangles, trapezoids and so on), or be regular circles, half circles or ovals. Or shapes may be organic or biomorphic—they have curved or flowing edges reminiscent of growing, living things, such as amoebas or trees, or naturally weathered materials, such as pebbles. They may have angular, broken, irregular shapes, like bark, lightning, thorns, or eroded metal.