There is a specialized branch of the turners' craft known as segmented turning. Like ornamental turning, it can be extremely labour-intensive, and produce spectacular results. I have to admit that I have never tried decorative segmented turning, and fear that I would not have the patience necessary. It appeals to people who like to immerse themselves in a project for however long it takes.
The essential feature of segmented turning is that the turning blank, which might become a bowl, vase or box, is carefully planned and constructed by the turner before the actual turning begins. Any number of separate pieces of wood, sometimes many thousands, are accurately sawn at precisely calculated angles, then glued together in stages to make a block that will be turned on the lathe. The pieces are normally of contrasting colours, and are arranged in a precise sequence in the block to make a pattern in the finished item. A simple example would be a brown and white chequered bowl like those you have probably seen, made of alternating 'bricks' of mahogany and sycamore. Sometimes the pieces are all of the same species and selected for their grain rather than contrasting colour. Great precision and accuracy are needed so that the pieces can be assembled without leaving any voids or prominent glue lines. Misalignment of the component parts will show in the end result.
Sometimes, gaps are deliberately left between the parts. The finished item will have a honeycomb appearance. The gaps might be regularly spaced, or even be used to make the finished item 'fade away' to nothing, perhaps on one side of a vase, as the proportion of 'gap' to wood increases.
The block can be built up to any size, enabling large turnings to be made without the problems that plain turners often face when using one single big chunk of wood, such as knots, cracks, bark inclusions etc. When the block is complete, it goes onto the lathe, carefully aligned, for turning in the normal way. The glued-up blank, which will have had a lot of time invested in it, may not have the strength of a solid block, so the turning is done slowly and carefully. A catch or dig-in with the tool could destroy all the work that has been done. Even the sanding and finishing need extra care to prevent the colour of one component piece bleeding over into the adjacent ones.
But if all goes well, the turning process reveals the pattern that was planned in the beginning. This may resemble mosaic tiling or basketwork, or it may be a pictorial design. The result can be very beautiful.
Segmented turning blanks are often made for purely practical reasons - small pieces are built up simply to make large blanks, without attempting to make patterns. If the pieces are placed end to end in a ring, there will be no exposed end grain in the blank, making the subsequent turning and finishing easier. It also avoids short-grain sections in the ring, making the end result much stronger than if made from a single large piece of wood. I make large horizon rings for globe stands by joining short boards end to end, and join boards edge to edge to make large discs.
Here are some splendid examples of decorative segmented turning: