To truly sharpen your flat-bladed tools, I recommend investing in some Japanesewater stones. These come in a variety of sizes and hardnesses. True to theirname, they should be soaked in water for at least ten minutes prior to workingwith them. In the photo above, you may see (from left to right) anadjustable 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 gritpolishing stone.
Inorder for your tools to be sharpened effectively, your sharpening stones must be perfectlyflat. The only way to do this is with the lap stone, which is far harder thanyour hardest stone and yet coarse enough to remove the high spots. This stone issoaked, too, and the smaller sharpening stones are passed over it vigorously. Besure to check your surface often to make sure you do not take off too muchmaterial. Once your stones are true, you are ready to begin shaping the surface.
Ifyou have a chipped or broken blade tip, you can reshape it using the side ofyour coarse stone. With the edge up, move the tool back and forth in a straightline, shaping the tip to a good point. This will groove the stone, which is whywe use the edge instead of the surface. Once your point is properly shaped, itis time to proceed to sharpening the tool.
How your tools are shaped
Lookclosely at the blades of a grafting knife (or your better bonsai shears). If youhave a new one, this will be the most instructive. You will find that theseblades are not shaped like your household scissors or any other pair of pruningshears. Where most knife edges are formed where two angled planes meet, agrafting knife edge is formed where a flat (actually slightly concave) facemeets a long, flat, beveled edge. Examine the photograph carefully. You will seea fine line about a quarter inch from the edge of the blade. This is not abeveled edge, it indicates where the layer of better steel is laminated to thebody of the blade. The entire polished face of the blade is a single plane,honed to an edge a few molecules across.
Whereother scissors or shears are designed witha definite bevel at the cuttingedge (to make sharpening easier and to enable the edge to last longer), bonsaishears are designed so that the back face and front face meet at a very acuteangle. Thus a single edge is formed, making possible the sharpest cutting edgepossible. The most important point when sharpening a blade like this is to honethe 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 thisinformationtranslate into actually forming that edge?
Making an edge
Thekey to forming a good edge on your flat-bladed tools is in your honing tools andthe proper angle of attack, as it were. As you can see at the right, a shadow isformed if the edge of the blade is held too high. This angle will merely roundoff 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 neverbe sharp enough to slice the living tissue of the tree without damaging it. Forthe best results, the face of the blade must be kept in full contact with thesharpening stone throughout the sharpening process. The photo above shows theproper angle for a pair of bonsai shears, while below is incorrect.
Assharpening progresses, a slurry will form, made of material from the sharpeningstone and the blade. It is important that this slurry remain on the stone tofacilitate sharpening of the blade. As the moisture in the stone drops, it iscrucial that it be kept wet. You can add fresh water, but it is easier to keepthe slurry if you reuse the water that has drained from the stone, as it hassome slurry already within it. Always keep your stone wet and your slurry inplace.
Theprocess, once you are comfortable with the position of the tool against thestone, is one of nearly mindless repetition. Many strokes are required toproperly shape a dull blade. One with gouges in the edge may need grindingbefore it can be properly honed. Be careful of your fingertips. I have yet tocut myself on a blade, but I have worn off several fingernails and fingertips bycarelessly rubbing them against the stone. As you make progress, you will wantto 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 finestedge, making the smoothest cuts, helping the tree to heal itself quickly andeasily.