The science of bonsai tools

As you probably have noticed, you can’t just walk into a home depot or garden store and pick up some bonsai tools. Bonsai tools are special. Each tool is specific to the task. In bonsai, we study how trees grow, even down to the cellular level. We must know how the tree responds to injury or pruning, and according to those facts, bonsai tools have been designed to minimize injury and promote healing. It has been my experience that many of my students at first are confused because they believe that making a bonsai means forcing a tree to become stunted. Some even have believed that we must torture the tree into submission. Nothing can be farther from the truth. One of the first things I teach my students about bonsai is that everything we do is to promote good healthy growth. When the tree needs pruning, properly maintained tools will actually make the tree grow healthy. How is this achieved?

To answer this question, we must understand how tree cells will respond to blunt cuts versus sharp cuts. Blunt cuts will damage surrounding cells and what we perceive as a cut is actually crushing and ripping. This kind of cut is produced by tools that are not sharp enough or tools that are improperly designed (I’m looking at you gardening tools). For example, gardening tools like pruning shears that you can buy in the hardware store have only one cutting edge. This cutting edge is never sharp enough to properly cut. The result will be that a significant amount of die-back will occur, making the tree expend energy in trying to heal its crushed cells. A sharp cut is much different and will significantly improve the trees health. Why? When the cutting edge is sharp, you are slicing the cells not crushing them. These tools will make clean cuts with no frays or biting. This minimizes the amount of dead cells, therefore minimizing the amount of energy the tree needs to expend on healing.

What tools to use

First things first, common gardening tools are not bonsai tools. When a student shows up with gardening tools to my classes, I tell them to leave the gardening tools in their car or at home. Gardening tools don’t deserve to be in the same room as bonsai tools. My bonsai basics students are encouraged to buy basic bonsai tools. These can start with cheap tools, for now… and as my students progress, I encourage my students to start buying quality tools. These will hold up much better and will last longer than cheap tool kits.

When you’re starting out, cheap Chinese tool kits may seem like good enough quality tools, but you will get what you paid for. Let me explain. All bonsai tools, cheap or otherwise are made from steel. The quality of the manufacturing and composition of the steel itself make a big difference.

Choosing the right types of steel

Let’s talk about metallurgy. Bonsai tools have different steel compositions. Regular steel is hard however will probably not hold an edge for very long. This type of steel is soft and probably won’t be tempered, can also be easily sharpened. It won’t hold an edge for very long. If the tool is made for cutting, this soft steel will produce nicks on the blade very easily. This is typically the type of steel found in cheap tools and kits.

Then there’s tempered carbon steel. Tempering steel is a process of manufacturing. After the tool has been formed, the steel (usually just the cutting edge) is heated until red hot and quenched rapidly in water. The heating of the metal will loosen the metal and carbon molecules, reducing the stresses produced by forming the tool, and then suddenly quenching the metal so as to freeze and crystalize the metal. Tempering produces a hardened metal however, because it has crystalized it is more brittle. This is why just the cutting surfaces are the once to be tempered. This hardened cutting edge will hold its edge however, it can chip easily so don’t drop the tool. The carbon content in this type of steel will produce not only a certain springiness to the steel so as to not bend but also make the steel harder without being tempered. Bonsai tools made with this type of steel will usually be more moderately priced and usually be sold as an individual tool rather than in a kit.

High carbon steel

High carbon steel bonsai tools are characterized as being higher quality tools. The higher content of carbon in the steel will increase the springiness of the steel so that if you need to squeeze hard on the handles, you don’t bend the tool. This type of steel tools will also include the tempered cutting edge. Tools made with this type of steel that are not cutting tools, such as pliers, don’t need to be tempered.  The tempering of high carbon steel will produce a very hard cutting edge, meaning that the edge will last longer without needing to be sharpened. However, they can rust very easily if not properly oiled after every use. Tools made with high carbon steel will be costly. Tools with this quality steel can go for as much as a few hundred dollars (usd). The type of steel, even with its draw backs, is ideal for bonsai tools.

High quality high carbon steel

Authentic high quality Japanese bonsai tools are carefully crafted. They are unique in their manufacturing. These manufacturers craft their tools in the same way they craft samurai swords.  Just like in making a katana (samurai sword) the steel is made into small slabs. Then the slab is folded in two, and then folded again, and again, until hundreds of layers are made. Once the layering process is done, forming the shape of the tool is made by pounding the steel into shape. Once formed, the cutting edge is then tempered and sharpened. This process produces a superior tool making them suitable for the wear and tear of bonsai professionals use. The cost associated with tools of this caliber, are usually not very feasible for hobbyist because of their high cost.

Stainless steel

Ah, stainless steel… now a days, stainless steel tools are all the rage in the bonsai world. They look nice. They are different from all the black colored tools everyone has. But is it really better than high carbon steel? First, what is stainless steel? Stainless steel is actually an alloy (a mixture of metals) that produces a type of metal that is resistant to staining or rusting. Stainless steel is usually composed of a mix of standard steel, chromium, carbon, and molybdenum. The amounts of each ingredient will dictate the quality of the steel. Bonsai tools made with this type of steel are harder, without the need of tempering. Stainless steel is known as austenitic grade metal, meaning that it cannot be hardened by means of heat treatment but rather by mechanical work or by pounding it into shape.

Let me say something about the quality of stainless steel. Not all stainless is made the same way. As I stated earlier, the content of each ingredient will dictate the quality of the steel. Some stainless steel will rust, meaning they have low molybdenum content. Some stainless will be too soft, meaning they have a low chromium and carbon content. When considering buying stainless steel bonsai tools consider this. The exact alloy content is expressed by number. Most stainless steel manufacturers will not tell you or won’t put the number on the tool. And even if they did, most people won’t know what those numbers mean.

I am not saying that all stainless bonsai tools are bad, there are certainly very good stainless steel tools out there, and I even own some. One of the biggest drawbacks for me personally, is that you cannot sharpen stainless steel with your normal sharpening stones. Because stainless is hard, it requires much stronger sharpening material usually in the form of diamond dust incrusted sharpening stone which can be expensive. Very few quality bonsai tool manufacturers produce stainless steel tools.

Are brand name tools the best?

So like everything you buy, prestigious brand names can mean you pay more, but are they really that much better? In most cases, yes. Now-a -days, manufacturing products are usually cheaper in countries like China. Even some Japanese brands are manufacturing their products in China, even multiple companies are being produced in the same factory. And that’s ok! Japanese brands, wherever they are manufactured, are usually good quality tools. Tools that have no name are usually cheaply made and cost around $20 (usd). One thing I will say is that you will get what you pay for. 

How to sharpen your tool

All tools; high quality, low quality, carbon steel, or stainless steel, all bonsai tools with a cutting edge will eventually get dull. So the question is what is the preferred method of sharpening your tools? Well, it depends on the type of steel your tool is made of. Any of the carbon steels require sharpening stones; stainless steel requires a diamond dust incrusted stones or diamond files.

Cheap tools are so cheap sometimes that it might be better to buy a new one rather than sharpen it. Besides it might not take an edge. Carbon steel can be sharpened with water stones. These stones use water as a lubricant between the edge that is being sharpened and the stone. The water also keeps the metal filings from clogging the stone. If you are using water stones to sharpen the tool, make sure that the tool is properly oiled before putting it away. When sharpening high carbon steel and folded steel, I recommend using an oil stone. For this type of sharpening stone, honing oil is used to lubricate the surface of the stone and keep the stone from clogging. The oil also prevents the steel from corroding. High carbons steel can start to corrode instantly if water is used. Stainless steel will need a diamond dust stone or more commonly found diamond files. Water can be used to lubricate the files.

Can a belt sander be used to sharpen bonsai tools?

Sharpening your tools with sharpening stones is very time consuming. In my case, it can take a few days to sharpen all my tools, So some have suggested using a belt sander with fine grit belts to sharpen. Here is the thing about using belt sanders: Using this method is basically rubbing the cutting edge of a tool against sand paper at high speed. This produces heat, that’s why it sparks when doing this. The heat will damage or make the tool lose the tempering of the cutting edge.

 How to prevent corrosion

What is corrosion? Corrosion is basically the metal trying to return to its natural state. Every metal corrodes. Some corrosion is good. Some metal corrosion actually protects the metal by creating a thin corrosion layer and protecting the metal underneath. High carbon steel can start to rust instantly if exposed to air, so what do you do? After every use, clean the tool and apply light oil. If you use your bonsai tools daily like I do, wd-40 works just fine. If you use your tools once a month or longer I would recommend camellia oil. Wd-40 tends to dry out after a few day and camellia oil will not dry out. Sword oil will work as well. Once you’re done oiling your tools, place them in a tool roll or in whatever else is your preference just as long as it’s clean and dry. I do not recommend placing your tools in a metal container such as a metal ammo box or similar metal containers. The contact of 2 similar or dissimilar metals will create an ionic exchange causing accelerating corrosion even if the tool has an oily film.

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