Action of the slicing blade on the wet wood.
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Leaf of ash veneer showing the "tight" and "loose" sides.
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Log opened up showing the plain sliced character of the wood.
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Counterfront showing "barber poling" or polarization.
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Cell Polarization
When veneer is Book Matched, alternating sections are turned over like the pages of a book. This reverses the angle of the cells that appear on the face. Thus, cells that pickup light on one side, cast a shadow in adjoining faces.
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There are three main types of
veneer slicing equipment used commercially.
- A rotary lathe in which the wood
is turned against a very sharp blade
and peeled off in one continuous or
semi-continuous roll;
- A slicing machine in which the
flitch or piece of log is raised and lowered against the blade and slices of the
log are made; or
- A half round lathe in which the
log or piece of log can be turned and
moved in such a way to expose the
most interesting parts of the grain.
Each of these types of processes
gives a very distinctive type of grain
depending upon the species. In any of
these veneer slicing methods, when
the veneer is sliced a distortion of the
grain occurs. The knife blade as it hits
the wood creates a "loose" side where
the cells have been opened up by the
blade, and a "tight' side. In the figure
to the right the tight and loose sides are indicated by the way in which the
piece of veneer bends or cups. The coloring differentiations created by the
tight and loose side should not be confused with the "barber poling" effect
which takes place in certain wood in
which the same piece of wood appears to be dark or light depending upon
which way it is viewed. This is caused
by polarization of the grain wherein the
grain is slightly angled from the surface, and depending upon where the
light source is coming from the grain is
either in shadow or is penetrated by
the light.
After veneer is sliced, the veneer
passes through a veneer screen dryer to bring
its moisture content down to approximately 8 - 12%. Upon exiting the dryer, bundles of veneer are made from
sequences of veneer leaves. Bundles
generally include 24 to 32 leaves.
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