How can you Verify that You’re Buying a Quality Knife?

It takes an outside source to confirm the claims of any cutlery brand.

It’s easy to say a knife cuts well, but some flaws go undetected by the human eye. Hard data is needed to verify which brands meet their claims, and which are fibbing. Shun undergoes numerous inspection phases. When they first arrive from Japan, the sharpening angles are checked by Kai USA experts. But after those initial evaluations, Kai sends Shun samples to independent laboratories for unbiased tests. What was found was eye opening.

Lisin Metallurgical Services has tested countless steel tools since 2000. Owner Mark Lisin’s mission is simple, but difficult in practice. Clients send in metal products that have failed for one reason or another.

“I get to look at everybody’s dirty laundry and figure out what things are made out of and why they work or don’t work,” Lisin said.

When you walk into the Milwaukie, Oregon office, the shelves are lined with previous jobs — metal tubes, gears, shafts, and more. Lisin’s job is to analyze the alloys and determine what went wrong in the failure. Shun works with the facility for a similar purpose. Only this time, the blade steel is tested before it has a chance to fail. Vice President of Product Development Tommie Lucas says that this step helps the customer.

“Like all things, accidents in heat treatment can happen,” Lucas admits. “Third-party testing facilities are not affiliated with Kai USA and can provide us with an unbiased opinion.”

When Shun samples arrive at the testing facility, Lisin inspects several elements. But first, it takes a little prep work to get started.

Revealing the Crystal Structure

Lisin uses his cutting tools to make a cross section and begin analyzing the knives. 

To analyze Shun, Lisin cuts off a sample of the blade in his workshop. This cross section will later be analyzed under a microscope. Creating this sample is fairly complex. A metallurgist must first grind the metal flat. It’s then polished to remove the grinding marks. Finally, the steel is etched in an acid to reveal the crystal structure of the metal. By the end of the process, you have a mirror finish that won’t show scratches under the miscroscope — just the structure of the metal.

“Essentially, you get it to where you can read these things like a book,” Lisin said.

With this sample in hand, Lisin puts it under the microscope. Based on his training, he can immediately tell how clean and homogenous the steel is. For example, carbon is sometimes lost during a poor heat treatment, which softens parts of the blade. Under magnification, this anomaly shows up as a light band. Ideally, the properties should be distributed evenly across the entire sample. In addition, it should be free from large, dark spots, which indicate that the steel is dirty.

These dark spots are non-metal compounds that form when the steel is made. Most failure points occur where the steel and the spots meet. Picture a ham sandwich. It’s easiest to separate the sandwich at the point where the ham and the bread meet. In a knife, this separation would manifest itself as chipping. That’s why it’s important to keep these dark spots as small, or “clean,” as possible.

After this visual analysis, testers use machines to find out more about the heat treatment.

Heat Treatment

Shun knives are cut in half for testing purposes, but because of their expert heat treatment, the steel stays strong during everyday use. 

As we explained in Part 2 of this series, heat treatment alters the steel to its ideal hardness. Most of the time, Shun craftsmen expertly heat and cool the alloy to the appropriate levels. But rarely, something goes wrong. Perhaps the steel is cooled for slightly too long, making the knife brittle. In short, the correct degree of hardness is a strong indicator of quality.

“I can tell you a great deal about the properties of a metal, how strong or ductile it is, just by measuring hardness,” Lisin said.

Thankfully, third-party testing ensures that defects never reach store shelves.

Lisin has access to a variety of methods for testing the hardness. Both Kai and Lisin use a Vickers Rockwell Hardness Tester. The Rockwell Scale is a common measurement for determining hardness. To do this, the machine’s needle-like indenter presses down on the steel, creating a tiny mark on the blade. It measures the depth to discover the hardness. If that number is outside Shun’s claims, we destroy the knives and order an improved batch.

But Lisin goes further than that. A microhardness tester provides a precise measurement right at the cutting edge. The machine makes several small indents. If these measurements show a variation in hardness, Lisin knows that the grind was probably overheated during heat treatment. As a result, an uneven mixture of hard and soft spots appears along the edge. This is less than ideal. 

To demonstrate, Lisin pointed at the middle surface of the blade. “You don’t need hardness back here,” the metallurgist said. “You need it at the edge. So that’s where we should test.”

Lisin uses an electron microscope to measure the cutting angle, which should be 16 degrees on each side. Additional tests are outsourced to other third-party facilities. For example, laboratories check the alloy chemical composition. They list each element found in the steel in order to verify that it’s genuine.

All of these factors are compiled in a report that’s sent back to Shun. If something is wrong, Kai takes appropriate action.

Feeling a bit more relieved? With third-party testing, Shun takes steps that other brands ignore. For extra protection, Shun knives are covered by a Limited Lifetime Warranty. Check back next time to learn more about warranty service.

Read More About Shun Quality 

Part 1

Part 2

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