Green vs. Dried Wood
Some items were made from green (recently harvested) wood and some were made from wood that had been sawn into boards and dried. For the purpose of this discussion, we are talking about furniture scale work. Small items (bowls, spoon, etc.) could be made from literally anything green or dry.
Working green wood is easier than working dried wood. The wood fibers are softer and sever more easily so your tools don't dull as fast. It's much easier to remove material in large chunks. The resulting boards are also stronger. The process yields boards where the fiber runs the length of the board. In sawn wood, it's cut straight regardless of the grain of the log.
On the downside, your tools will rust if you aren't careful. Fine work isn't possible until the wood dries at least a little. And your wood choice is constrained to ring-porous woods (see below).
Riving Wood
Splitting boards from logs is called riving. This is a process where you take a section of log that's as large a diameter as possible which is straight and has no branches. Using this process, the boards will be no more than about 40% of the width of the log you are starting with. So, say you have a 24" diameter log. You can expect to get, at best, 10" boards. Probably closer to 8" depending on the quality of the log.
You start by splitting the log in half. This is the hard part and is done with wedges and mallets. Then you split it into quarters. Split again. Continue to split until you get to the right size.
What's the right size? It's the smallest wedge that will give you the board you want. The pieces you have split out are wedge-shaped. However, you don't want the pith or the sapwood and bark as shown on the right. So you start by splitting or hewing those off. You are left with a trapezoid which you need to turn into a square. So, pick a face, we'll call that "flat", mark towards the other face the thickness you need and split off the rest. That part should have been an acute triangle.
Now you have a rough board ready to trim and plane to final dimensions. As noted above, this will be a strong and dimensionally stable board. And, if this is oak, will have a very attractive ray fleck like quartersawn but better. In fact, it's the best wood and you can't buy it. You can only make it with sweat equity. However, it's pretty
(oak, ash, elm, black locust).
