IAWA Journal, Vol. 24 (3), 2003: 241–245
APPLICATION OF THE “NT-CUTTER” KNIFE BLADE TO
MICROTOME SECTIONING OF WOOD
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
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
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.
The author would like to thank Dr. Ken Ogata for critically reading this report.