We're back with here). He's going to take us through the identification process for hardwoods.
David, where do we start?
You should prepare the surface of a wood sample before you examine its cells. Preparing the cross-sectional surface of a piece of wood properly can be frustrating and time consuming, but it is worthwhile. Make a thin, clean cut across the wood's surface with a sharp knife or razor blade. Make the thinnest slice possible to reduce tearing of the wood.
After removing the slice, use a hand lens or magnifying glass to look at the surface. Identifying wood is often a process of elimination. Look for different cell types and write down what you observe. Your notes will help you remember what you have seen and help you identify the wood.
Are there a lot of different cell types to learn? And are they easy to tell apart?
There are four major cell types, fiber tracheids, vessels or pores, longitudinal parenchyma, and ray parenchyma. All of the cell types are easily identified, so there is no confusion about what they are, and each one serves a unique function in the tree.
Are cells the only thing to look at?
No, that's just the start. After you determine a piece of wood is a hardwood, you should examine the pores in greater detail. Remember that hardwoods contain vessel elements, or pores, that softwoods do not have. You will want to examine the size, distribution, and changes in number of pores to identify the type of hardwood.
Hardwoods can be classified into three groups based on the pores:
• Ring-porous hardwoods, oaks and elms, have pores that transition from small to large abruptly from the earlywood to the latewood. The largest of the pores are clearly visible to the naked eye:
• Semi-ring porous hardwoods such as walnut, pecan, and hickory have pores that gradually change from small to large in a growth ring:
• Diffuse-porous hardwoods yellow poplar, gum, and maple have pores that are the same size throughout the growth ring:
Pores are also distributed in other ways in wood. They can be arranged as follows:
A. Solitary pores: Individual pores evenly spaced.B. Pore chains: Multiple pores chained together.C. Nested pores: Clusters of pores connected together.D. Multiple pore: Two or more pores clustered together.E. Wavy bands: Bands of pores with a wavy appearance.
There is actually a lot of difference in these woods. The pictures really help, thank you. So we have cells and pores, and…?
And we have wood rays which look like small stripes that go from one edge of a piece of wood to the other edge on the cross-sectional face. Wood rays transport food and water horizontally in the tree.
The rays in most species are unique and allow for easy identification. Oaks, for example, have very large rays that are visible to the naked eye. Sycamores can also be easily identified by the number of rays.
That's what makes "rift and quartered" flooring and other and other "figured" wood so distinctive, right?
Exactly. When you saw the lumber, you slice open these rays, making the surface patterns. But beyond the aesthetics, examining the tangential and radial surfaces of wood for the characteristics of rays can help you identify wood species. Rays vary both in height and width, so examining both surfaces is key. Looking at the tangential surface will allow you to look at ray height. Some rays are several inches tall, while others are difficult to see at all.
The rays in oak can be over an inch high (white oak) or less than an inch (red oak). Examining on the radial surface will allow us to see what is called the ray fleck, of the wood. The fleck is where rays have been cut longitudinally and give, in the case of oaks or cherry a "tiger stripe" effect.
If rays are present in every hardwood, why don't we see significant figure in most species?
Because many of the rays are only one cell wide, we call these unisariate rays. They can be so narrow in fact that without the aid of a microscope they can't be seen.
And why do rays seem to shine?
The angles of the cell walls and the parenchyma cells around them tend to make them catch light in a desirable way. Many of the woods we utilize are simply used because of the way light seems to dance back from their surfaces.
That helps so much! So next week tropical hardwoods?
I can do that.