Its still winter outside, and since most plants are dormant, this is a good time to look over your bonsai tools and to make them ready for spring use. Some may be dirty and others nicked or dull – a sure recipe for future problems. So let’s get them out of storage and get them in shape.
If you tools are dirty, they must be cleaned before re-sharpening or re-storage. Most tools and their cutting edges can be wiped clean with a cloth, but sometimes tree sap, stubborn dirt, or rust may be present. Wiping with a wet, soapy cloth will cure many problems, but sometimes turpentine, rubbing alcohol (isopropyl), or a hydrocarbon solvent (lighter fluid or paint solvent) is needed to remove sticky deposits. If one solvent doesn’t work, choose another until you get tools clean. If there is rust on a tool edge, light scrubbing with a rubber pencil eraser is a gentle fix; use of 0000 steel wool, emery/crocus cloth, and wire brushes is more aggressive. Heavy rust can be removed using Navy Jelly or a similar preparation. Cleaning the cutting surfaces is critical, since these mating edges have very precise angles and meeting surfaces; overly vigorous use of abrasives can ruin a tool or mandate re-sharpening.
Suppose that your tools need sharpening. Ideally, you should monitor their condition as you use them, never letting them get really dull. You will need sharpening stones to sharpen your tools. There are generally three kinds of stones to buy: natural (Arkansas or silicon quartz), man-made (India or aluminum oxide, and silicon carbide), and ceramic (man-made with precise abrasiveness). Any of these sharpening stones will work for our purposes, as long as they are properly shaped and as long as we have a range of abrasiveness (fine vs. coarse).
Flat stones are used for straight edges, and curved or rod stones are used for knob and side/branch cutters or for any curved surface. Additionally, flat stones are flat with no wavy surfaces. It is important that the stone be fixed or secured on a bench, so that it doesn’t move when the tool’s edge is drawn across it. Some kinds of stones are best used “wet”, that is with a cutting fluid or water to keep removed particulates in suspension and away from the sharpening edge. One starts with a coarse stone, especially to remove nicked surfaces or to sharpen a really dull tool. Then one progresses to a finer abrasive to smooth the surface. The real secret to obtain satisfactory results is to maintain the same cutting angle throughout the sharpening process. This can be very difficult but is imperative to obtain good results. Sharpening a straight edge, one keeps the flat and beveled edges flat against the stone surface, generally moving the edge in a circular motion.
Sometimes you only sharpen part of the cutting edge. For example, with anvil blades, only the top blade is sharpened, but the blade is sharpened and beveled on both sides – much like sharpening a knife. Concave and knob cutters have complex cutting surfaces – maybe too difficult for an amateur to do. Both types of cutters are sharpened only on the inside of the tool with a curved stone, round or half-round, to maintain the beveled edge. However, the actual edges are perfectly mated along the entire cutting edge.
After one uses the various stones to get the proper sharpness, a final step of honing is performed. Here, the edges are not sharpened, but are smoothed to removed any burs or rough spots. This is analogous to stropping a straight razor at a barbershop. In fact, leather-stropping straps can be used with straight bonsai tool edges. Very fine pieces of porcelain can be used for curved surfaces. Sometimes tools must be adjusted to cut better or to change the amount of overlap (straight edges) by adjusting the hinge screw tension, by removing small amounts of metal at the hinge, or by peening the hinge rivet.
Finally, the tools – especially the cutting surfaces – should be well oiled before they are put away for the winter. In fact, after any tool is cleaned or sharpened, it’s a good idea use oil or WD-40 to prevent rust. Your tools will last for many years and perform well if you take care of them and keep them sharp.