Japanese Polishing (kenma) is an essential finishing technique that brings out the beauty and texture of crafts. This process of smoothing surfaces not only enhances the visual appeal but also significantly impacts durability and comfort of use by maximizing the natural luster and tactile qualities of materials.
This article introduces the characteristics and processes of different polishing techniques for materials such as metal, wood, ceramics, and glass in an easy-to-understand manner. By exploring the world of “polishing” that supports the appeal of crafts behind the scenes, you’ll develop a deeper understanding and appreciation for these works.
Table of Contents
What is Japanese Polishing? Explaining the Basics and Appeal of Finishing Techniques
Japanese Polishing is a “finishing technique” that smooths the surface of materials to enhance both appearance and function. Unlike cutting, it uses fine particles to create a smooth polish that dramatically improves the quality and texture of products.
Here, we’ll introduce everything from the basics of polishing to the tools used and types of finishes in an easy-to-understand way.
How Does It Differ from Cutting? The Role and Process Differences of Polishing
While both polishing and cutting are material processing techniques, they have clear differences in purpose and application. Cutting uses tools or blades for “rough processing” to mainly shape the material.
In contrast, polishing is a “finishing process” that finely adjusts the surface to refine the final texture and luster. In other words, if cutting is “creating shape,” polishing is “finishing the beauty and performance.”
The 3 Fundamentals of Polishing! Abrasives, Buffs, and Compounds
Among the tools and materials used for polishing, particularly important are abrasives, buffs, and compounds.
By skillfully combining these, it becomes possible to properly polish various materials from metals to glass and plastics.
Abrasives
Abrasives are particles that have the role of cutting surfaces, with different hardness and sizes to adjust the coarseness of the polish.
These hard particles are the main players in polishing.
They are used to cut the surfaces of metals, glass, and other materials, and are attached to paper, cloth, whetstones, etc. for use.
- Examples: Alumina, silicon carbide, diamond abrasives
- Uses: From rough cutting to precision polishing
Buffs
Buffs are polishing tools made of cloth or felt that evenly apply abrasives to surfaces.
These soft polishing materials made of cloth, felt, and other materials are used for polishing.
They are rotated to polish surfaces and create shine.
- Types: Cloth buffs, felt buffs, wool buffs, etc.
- Uses: Mirror finishing and final polishing
Compounds
Compounds are paste-like polishing agents containing abrasives, with many varieties depending on their purpose.
These pastes or liquids mixed with abrasives are applied to buffs or cloth.
Using them allows for removing fine scratches and adding gloss.
- Composition: Polishing particles + base substances like oil or wax
- Uses: Finishing polishes for automobiles, metals, and plastics
Finish Differences Determine Beauty! 3 Types of Polishing Finishes
Polishing finishes mainly come in three types: “mirror,” “satin,” and “matte.” Each texture has clear differences and is selected based on purpose.
Mirror Finish
Mirror finish makes the surface shine brilliantly like a mirror and is used for products where a premium look is desired.
Satin Finish
Satin finish features a subdued luster with fine lines, with the advantage that fingerprints are less noticeable.
Matte Finish
Matte finish is a non-glossy texture that doesn’t reflect light much, giving a soft and warm impression.
All of these finishes are important elements in enhancing product appeal. Choosing the optimal finish according to design and intended use is key to increasing product value.
Understanding Material-Specific Polishing Techniques and Finish Differences!
Polishing techniques vary greatly depending on the characteristics of the material. From metals where strength and luster are emphasized, to gems and glass where transparency and reflection are maximized, to lacquerware and woodwork where touch and gloss are vital, there is an optimal polishing method for each material.
Here we introduce three representative materials and their techniques and characteristics.
Metal Polishing: Techniques That Balance Luster and Precision
Metals like silver, copper, and stainless steel require attention not only to visual beauty but also durability and rust resistance. In the early stages, barrel polishing is used to create uniform surfaces, followed by buff polishing and electrolytic polishing as finishing processes.
For mirror finishes in particular, the surface is polished using a buff impregnated with compound to achieve a mirror-like reflection. The range of processing options is wide, depending on purpose and cost.
Gem and Glass Polishing: Cuts and Precision That Bring Out Brilliance
In gem polishing, facet cutting is one of the most important elements. The angle and symmetry of cuts greatly influence light reflection and refraction, determining the gem’s “brilliance.” For glass, which is a hard material that needs to be smoothed, diamond tools and fine polishing agents like cerium oxide are used.
These require high-precision processing and the advanced skills of a lapidary (a craftsperson who cuts and polishes stones).
Lacquer and Woodworking Polishing: Traditional Techniques That Create Texture and Luster
Lacquerware and wooden items value not only gloss but also texture and material feel, so unique polishing methods are employed. “Togiko-togi” is a method of creating even surfaces using abrasive powder dissolved in water to smooth layers of lacquer.
“Sumi-togi” is even more delicate, using charcoal to polish by hand, creating a soft luster and deep texture. These techniques are essential processes in traditional Japanese crafts, supported by the craftsperson’s sensibility and skill.
Selecting the optimal polishing method for each material is key to maximizing the completeness and appeal of a work. Polishing is an important technique that directly affects not only visual beauty but also touch and durability.
How to Choose Equipment and Consumables to Streamline Polishing Work
To improve the quality and efficiency of polishing work, selecting appropriate equipment and consumables is essential.
The performance of disc grinders and rotary tools, the grit of whetstones and pads used, and the preparation of the work environment greatly impact the finished product and worker safety. Below, we explain each element in detail.
Characteristics of Disc Grinders and Rotary Tools
When choosing disc grinders or rotary tools, the balance between torque and rotation speed is important. High-speed rotation types are suitable for cutting metal, while low-speed high-torque types are suitable for polishing work.
Additionally, variable speed types can adjust rotation speed, allowing flexible responses to materials and work content. Selecting the appropriate type for the work content is key to achieving efficient and high-quality finishes.
Choosing Whetstone and Pad Grits Based on Material Characteristics
Selecting the grit of whetstones and pads used for polishing directly affects the quality of the finish. Generally, coarse whetstones are around 220 grit, medium whetstones around 1000 grit, and finishing whetstones 5000 grit or higher. For hard ceramic materials, diamond whetstones are suitable for efficient polishing. Choosing appropriate whetstones and pads according to material characteristics and purpose leads to improved work efficiency and quality.
Dust Prevention and Collection Systems Are Important in Polishing Work
Dust generation is unavoidable in polishing work. Ignoring this can lead to health hazards for workers and deterioration of the work environment. Therefore, implementing dust prevention and collection systems is important. By moistening or sealing to prevent dust dispersal and using dust collectors or exhaust equipment, the work environment can be kept clean. Clean room specifications and wearing dust masks are also effective in protecting workers’ health.
By comprehensively considering these elements and selecting appropriate equipment and consumables and preparing the work environment, the efficiency and quality of polishing work can be significantly improved.
Critical to Quality! Correct Measurement and Inspection Methods After Polishing
Accurate measurement and inspection are essential to confirm the final finish of polishing and surface treatments. In particular, surface smoothness, presence of scratches, and coating durability directly affect the product’s appearance and functionality.
Here, we explain the representative inspections that should be performed to ensure product quality and their key points.
Using Ra and Rz Measurements to Numerically View Surface Smoothness
The most common method for numerically managing polishing quality is measuring surface roughness. The representative indicators are “Ra (arithmetic mean roughness)” and “Rz (maximum height),” which are standardized by international standards such as ISO and JIS. Ra indicates the degree of average unevenness, while Rz shows the maximum difference in surface unevenness. These are measured using stylus or laser roughness meters, and the quality of the finish is judged by comparing with design standards.
Don’t Miss Even Small Scratches with Optical Microscope Scratch Inspection
Optical microscopes are effective for checking microscopic scratches or coating peeling on surfaces that are invisible to the naked eye. In particular, a method called “scratch testing” evaluates the degree of scratching by using a pointed needle (stylus) to scratch the surface. This numerically evaluates film adhesion, hardness, durability, etc., helping to confirm processing accuracy and investigate causes of defects. High-magnification observation enables detection of easily overlooked defects.
Confirming Coating Durability with Corrosion Resistance and Film Thickness Measurements
Whether a product can be used stably over a long period depends on the “durability” of its surface treatment. Particularly for metal products and decorative components, inspection of coating film thickness and corrosion resistance performance is necessary.
Film thickness is measured in microns using electromagnetic or eddy current film thickness gauges to confirm uniformity and minimum required thickness. Additionally, corrosion resistance tests, such as salt spray tests, are important for verifying practicality in outdoor or high-humidity environments in advance.
By reliably performing these inspections and measurements, product reliability is substantiated while improving quality control accuracy. Understanding and implementing measurement equipment and standards is essential for compliance with domestic and international quality standards.
Environmental Considerations and Sustainability Are Major Challenges in the Polishing Industry
In the polishing industry, environmental considerations and sustainability have become important issues. Below, we explain in detail the environmental initiatives in the polishing process.
Regeneration of Polishing Sludge and Utilization of Recycled Metal
For example, SUN METALON and Komatsu have begun joint research on a new recycling process that regenerates iron-based polishing sludge into high-purity metal resources. This initiative is expected to reduce waste and effectively utilize resources.
Technology is also being developed to use polishing sludge as recycled aggregate. For instance, efforts are being made to modify sludge cake into sand-like substances for reuse as ground improvement materials or admixtures. Such technologies have the potential to contribute not only to waste reduction but also to CO₂ reduction.
Use of Water-Soluble Compounds and Efforts to Reduce VOCs
Many compounds used in polishing work contain organic solvents, and the emission of volatile organic compounds (VOCs) has become a concern. In response, the use of water-soluble compounds is being promoted. Water-soluble compounds suppress VOC emissions and contribute to improving the work environment.
For example, the ALMA series of water-soluble compounds has attracted attention as a product that reduces environmental impact while maintaining excellent polishing performance.
Furthermore, at work sites, efforts such as strengthening ventilation equipment and reviewing work procedures are being made to suppress VOC emissions. This makes it possible to prevent health hazards to workers and minimize environmental impact.
Promotion of Environmental Management Based on ISO 14001
For example, the Misumi Group conducts annual internal audits to confirm the operational status and effectiveness of its environmental management system and to horizontally deploy good environmental activity practices, while also undergoing external audits by ISO14001 certification bodies. Additionally, they provide environmental education to employees based on an environmental education and training plan to strengthen their environmental management system.
Through these initiatives, companies establish systems for reducing environmental impact and ensuring legal compliance, realizing sustainable management. It will continue to be necessary to balance technological innovation with environmental considerations.
Summary
Japanese Polishing is not merely a finishing process but an important procedure that maximizes the appeal of materials and determines product quality and reliability. By utilizing different techniques and tools for materials such as metals, gems, and woodwork, optimal finishes can be achieved for specific purposes.
Furthermore, by evaluating polishing results numerically through accurate measurement and inspection, quality control based on international standards becomes possible. Selection of polishing equipment and consumables, as well as workshop operation including environmental measures, have become important elements in sustainable manufacturing.
In the future, polishing technology will likely evolve in more precise and eco-friendly directions.
