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IAWA Journal, Vol. 24 (3), 2003: 241–245 APPLICATION OF THE “NT-CUTTER” KNIFE BLADE TO MICROTOME SECTIONING OF WOOD by Tomoyuki Fujii Forestry and Forest Products Research Institute, Tsukuba Norin P. O. Box 16, Ibaraki 305-8687, Japan Traditional microtome knives were popularly used for sliding microtome sectioning of wood samples. It was usual to produce several sets of microscopic slides from only one wood block per day (several sets of cross, radial and tangential sections) in the Wood Anatomy Laboratory of the Forestry and Forest Product Research Institute, because it was time-consuming to sharpen the knife-edge worn by the sectioning. In the late 1970ʼs, the introduction of a microtome blade holder with a disposable knife blade (Holder No. 160 with Blade type S35, Feather Safety Razor Co. Ltd., Japan) saved much time by exchanging a worn blade to a new one, and eliminating the sharpening procedure. It is now common to produce microscopic slides from several to 10 wood samples per day. Furthermore, the fine edge of the blade has enabled the constant production of high quality sections. However, the popular disposable knife blade (Fig. 1b: Feather S35) could some- times not be used for heavy timbers without previous softening, especially for prepar- ing cross sections. Feather Safety Razor Co. Ltd. offers a line-up of various types of blades, but those blades have the same thickness and width as Feather S35. Recently, a microtome blade specially designed for thin sectioning of resin-embedded samples for optical microscopy (Microtome blade H35S, Feather Safety Razor Co. Ltd., Japan) has become available (Fig. 1a) with the blade holder Feather No. 158HD. It is thick and rigid enough to cut large cross sections of very hard timbers, but the the blades are very expensive (Table 1). A special knife was invented originally for cutting paper in the printing industry in Japan in the late 1950ʼs. It is a knife holder with a disposable blade of which the edge Fig. 1. Knife blades: a: Feather H35S b: Feather S35 c: NT-Cutter blade A-type d: NT-Cutter blade L-type 242 IAWA Journal, Vol. 24 (3), 2003 Table 1. Specifications of knife blades. Blade thickness width length edge material of body List price (mm) (mm) (mm) angle (°) unit Feather S35 0.254 8.0 80 35 stainless steel ¥ 8,500 / 50 blades H35S 0.8 14 80 35 stainless steel ¥ 35,000 / 10 blades NT-Cutter L-type 0.45 18 100 carbon steel SK-2 ¥ 700 / 50 blades A-type 0.38 9.11 80 45 carbon steel SK-2 ¥ 1,200 / 50 blades can be snapped off to expose a new sharp tip. NT-Cutter L-type (NT Inc. Japan, Fig. 1d: spare blade), which is one of the original types and most popular for heavy duty use, has been used for hand sectioning of wood samples, and sufficiently large cross sections can be prepared even from heavy tropical timbers from South-east Asia. However, microtome sectioning is superior to hand sectioning for micrography and also for the production of multiple sets of microscopic slides of constant quality. Consequently, the microtome blade holder (Feather No.160) was remodeled to hold a spare blade for the “cutter knife”. Here, the NT-Cutter blade A-type (Fig. 1c) was selected because of the size close to the Feather S35 microtome blade instead of the wide L-type (Table 1). The ditch of the remodeled holder was a little wider and deeper than the original (Feather No.160 NT-A, Table 2). With the application of the blade holder remodeled for the A-type blade to micro- tome sectioning (Fig. 2), fine sections of 10–15 microns thick were obtained without the extremely careful adjustment of the block orientation which is usually required when sectioning with microtome blade Feather S35. As a trial, more than 10 sets of three different sections were produced from Japanese hard- and softwood samples Fig. 2. Microtome section- ing of Distylium racemo- sum wood with the blade holder remodeled for a NT- Cutter blade type-A. Fujii — New knife blade for sectioning heavy woods 243 Table 2. Specifications of microtome blade holders. Knife holder length width thick- ditch ditch material of body unit (mm) (mm) ness depth width (mm) (mm) (mm) Feather 160 160 45 12 0.35 7.2 Dies steel (SKD-11) Feather 160 NT-A 160 45 12 0.66 7.6 Dies steel (SKD-11) Feather No. 158HD 158 45 10 Dies steel kept in a mixture of glycerin and ethanol. As a result of two-days intensive work, 33 samples were sectioned. They included relatively heavy timbers, wood samples with slightly wavy grain, and also very small-diameter samples of shrubs and lianas. For example,very large cross sections were obtained from Quercus crispula (Fagaceae, Fig. 3. SEM micrographs of Eusideroxylon zwageri in cross section coated with Pt-Pd. – a: low magnification; b: enlargement of a part of Fig. 3a illustrating a vessel filled with tylosis sur- rounded by aliform parenchyma and thick-walled fibers. Fig. 4. Micrographs of Eusideroxylon zwageri stained with safranin and gentian violet. – a: cross section; b: radial section; c: tangential section. 244 IAWA Journal, Vol. 24 (3), 2003 air dry density: 0.6–0.9 g/cm 3) and Distylium racemosum (Hamamelidaceae, air dry density: 0.86 g/cm 3 ), and the quality of the sections was such that wide and narrow vessels were without apparent damage to their cell walls. One blade was long enough to cut three different sections (Fig. 2). Once a part of the blade was used for sectioning the blade holder was slid longitudinally and a new sharp part of the edge was used for subsequent sectioning. On that occasion, the rela- tive level of knife edge to the section surface of the sample was so constant (as in the case of Feather S35) that only one stroke was enough to adjust for a new section. A typical example is illustrated by sections of the most heavy timber species in South-east Asia, Eusideroxylon zwageri (Lauraceae, air dry density: 1.09 g/cm 3 ). The cross section of the sample was unavoidably restricted to a narrower width than those of the wood samples of Japanese heavy hardwoods (Fig. 3a). Thick-walled fibers were sectioned as well as vessels and axial parenchyma cells, and apparent knife marks were not observed after cutting several cross sections (Fig. 3b). Small cracks were generated in fibers when the curled sections were flattened (Fig. 4a). Longitudinal sections such as radial and tangential sections (Fig. 4b & c) can be cut with a sliding microtome equipped with an ordinary disposable knife blade (Feather S35), but it requires careful adjustment of block orientation. In contrast, the NT-Cutter blade applied to microtome sectioning did not require such careful adjustment. Fig. 5. SEM micrographs of a NT-Cutter blade at different angles without coating. – a: side view at low magnification; b: edge of the knife blade; c: the point of the blade edge at high magnifica- tion; d: sectional view of the edge. Fujii — New knife blade for sectioning heavy woods 245 The A-type blade is thicker than the Feather S35 blade (Table 1). SEM investigation revealed the straightness of the edge (Fig. 5a) and obvious grinding marks perpendicular to the edge on the blade surface. Only the tip of the edge appeared smoothly polished (Fig. 5b), although gentle marks were still observed there at higher magnification (Fig. 5c). This rough edge surface is quite different from the thoroughly smooth edges of Feather S35 blades. The edge angle is 45° as measured using a tilting apparatus in the SEM (Fig. 5d) and is distinctly more obtuse than that of the Feather S35 blade. ACKNOWLEDGEMENT The author would like to thank Dr. Ken Ogata for critically reading this report.
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