Wood under the microscope
Just as we all have different fingerprints, every wood has unique anatomical features. In many cases these features are extraordinarily beautiful. In many cases, identification to species level is not possible.
Wood identification is necessary for a variety of reasons. For example, European legislation requires that care is taken to only purchase wood from legal and sustainable sources. It follows that it is necessary to check that what has been supplied really is what it was supposed to be,
Again, in building conservation, engineers need to know the species so that they can assign strength grades to timber.
When identifying hardwoods (broad leaved trees), very often all that is needed is a x10 pocket magnifier and a sharp knife. The features observed on the cross section (transverse section or TS) give most of the information, but the side views can also be important. If you were to imagine looking in under the bark, we would call this the tangential longitudinal view or TLS. The third view is looking into a radial surface or radial longitudinal surface (RLS). In all the images below, thin sections have been cut with a microtome that are just 0.02mm thick. They would be quite transparent unless stained to reveal the anatomy. Typically we use a red stain. After noting the features, they can be compared with a key.
When examining softwoods (from cone bearing trees), we can only identify them using a high power microscope with magnifications of 50, 200 or 400 times. Whilst all the surfaces must be examined, the most helpful view is the radial view RLS. Some of the images below have very beautiful red and blue colouration. This particular microscope was fitted with an expensive accessory called Nomarski interference contrast, which very helpful in making the various features stand out. However, quite modest student microscopes are perfectly adequate. Indeed you will note that some of the images have not been stained and yet the anatomy is very clear.
If you wish to learn more then contact the Wood Technology Society at firstname.lastname@example.org. Occasional 'Introduction to wood identification' days are held at modest cost.
We also draw your attention to an article on illegal logging from the magazine Materials World, which makes reference to the Royal Botanical Society at Kew and its collection of over 42,000 microscope slides.