Hi Mike
Patrick Spielman explained the differences between intarsia and segmentation in his Scroll Saw Segmentation book:
"Segmentation projects are, as a rule, made from just one board or a single piece of inexpensive material. The process involves cutting out patterns of objects, such as fish, animals, scenery, and the like, into primary elements or segments (tails, wings, legs etc), separating them from the whole. The edges or surfaces of each part are rounded over or otherwise contoured and shaped with hand or power tools. A pigmented color, stain, or natural finish is applied to the individual segments. Lastly, the segments are reassembled with wood glue to re-create the whole.
Intarsia, on the other hand, requires selecting stock from many different boards or pieces of wood in different natural colors - usually in dark-, medium-, and light-toned combinations. Sometimes one to a dozen or more different species of wood are used to make up the colors for the individual segments. Walnut and maple, for example, provide a dark brown and white that may be combined with various pink shades of Western cedar to create a colorful palette. Usually clear, natural finishes are used.
Each piece of wood selected for an intarsia project is chosen for its natural color as well as its figure, or grain, direction, which complements the general design effect. Each segment of intarsia, however, is cut individually and must be made to fit precisely against adjoining segments. Thus, in addition to using more expensive materials, intarsia is more labor-intensive and somewhat more difficult to accomplish overall."
Gill