Sharpening Flat-Bladed Bonsai Tools
The
care and sharpening of good bonsai tools is of paramount importance. Dull blades
tear plant tissues, making healing difficult. Dirty, rusty blades carry
pathogens from tree to tree, spreading what may have been contained otherwise.
Tools in poor condition subject you to ridicule and derision and the
embarrassment of that look your sensei gives you.
To truly sharpen your flat-bladed tools, I recommend investing in some Japanese
water stones. These come in a variety of sizes and hardnesses. True to their
name, they should be soaked in water for at least ten minutes prior to working
with them. In the photo to the right, you may see (from left to right) an
adjustable base support, a lap stone, a coarse Japanese water stone (240 grit),
a combination stone from Joshua Roth (280/1500), and a combination stone
(800/4000). All these items and more are available from
Woodcraft. I use four stones in succession, 240, 800, 1500, and 4000.
Woodcraft also sells an 8000 grit
polishing stone.
In
order for your tools to be sharpened effectively, your sharpening stones must be perfectly
flat. The only way to do this is with the lap stone, which is far harder than
your hardest stone and yet coarse enough to remove the high spots. This stone is
soaked, too, and the smaller sharpening stones are passed over it vigorously. Be
sure to check your surface often to make sure you do not take off too much
material. Once your stones are true, you are ready to begin shaping the surface.
If
you have a chipped or broken blade tip, you can reshape it using the side of
your coarse stone. With the edge up, move the tool back and forth in a straight
line, shaping the tip to a good point. This will groove the stone, which is why
we use the edge instead of the surface. Once your point is properly shaped, it
is time to proceed to sharpening the tool.
How your tools are shaped
Look
closely at the blades of a grafting knife (or your better bonsai shears). If you
have a new one, this will be the most instructive. You will find that these
blades are not shaped like your household scissors or any other pair of pruning
shears. Where most knife edges are formed where two angled planes meet, a
grafting knife edge is formed where a flat (actually slightly concave) face
meets a long, flat, beveled edge. Examine the photograph carefully. You will see
a fine line about a quarter inch from the edge of the blade. This is not a
beveled edge, it indicates where the layer of better steel is laminated to the
body of the blade. The entire polished face of the blade is a single plane,
honed to an edge a few molecules across.
Where
other scissors or shears are designed with a definite bevel at the cutting
edge (to make sharpening easier and to enable the edge to last longer), bonsai
shears are designed so that the back face and front face meet at a very acute
angle. Thus a single edge is formed, making possible the sharpest cutting edge
possible. The most important point when sharpening a blade like this is to hone
the entire front face of the blade, removing material evenly across the face,
providing an edge that is ultimately sharper than a razor. But how does this
information translate into actually forming that edge?
Making an edge
The
key to forming a good edge on your flat-bladed tools is in your honing tools and
the proper angle of attack, as it were. As you can see at the right, a shadow is
formed if the edge of the blade is held too high. This angle will merely round
off the back of the blade, and nothing will be accomplished. On the other hand,
if the back of the blade is raised, the edge will form a bevel, which will never
be sharp enough to slice the living tissue of the tree without damaging it. For
the best results, the face of the blade must be kept in full contact with the
sharpening stone throughout the sharpening process. The photo at left shows the
proper angle for a pair of bonsai shears.
As
sharpening progresses, a slurry will form, made of material from the sharpening
stone and the blade. It is important that this slurry remain on the stone to
facilitate sharpening of the blade. As the moisture in the stone drops, it is
crucial that it be kept wet. You can add fresh water, but it is easier to keep
the slurry if you reuse the water that has drained from the stone, as it has
some slurry already within it. Always keep your stone wet and your slurry in
place.
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The
process, once you are comfortable with the position of the tool against the
stone, is one of nearly mindless repetition. Many strokes are required to
properly shape a dull blade. One with gouges in the edge may need grinding
before it can be properly honed. Be careful of your fingertips. I have yet to
cut myself on a blade, but I have worn off several fingernails and fingertips by
carelessly rubbing them against the stone. As you make progress, you will want
to move to finer stones until you are satisfied with the sharpness. Ultimately,
the goal is to polish the face to a mirror surface. This will ensure the finest
edge, making the smoothest cuts, helping the tree to heal itself quickly and
easily.
