Abrasives for Urushi and Kintsugi: Exploring the Different Options

Introduction

When beginning kintsugi, working with urushi lacquer or exploring how professional kintsugi repairs are undertaken, it is easy to assume that sandpaper is the only material needed for smoothing and finishing.

In reality, there is a much wider range of abrasives available, including natural materials that have been used in Japanese craftsmanship for generations and modern products developed for automotive finishing and other demanding applications.

Each has its own characteristics. Some are flexible, others rigid. Some are particularly useful for flattening a surface, while others are better suited to curved areas, delicate repairs or preparing a lacquered surface for polishing.

This article explores the different options, including some inexpensive and readily available alternatives.

1. Ordinary Sandpaper and Wet-and-Dry Paper

For most beginners, ordinary sandpaper is the obvious starting point.

It is inexpensive, widely available and comes in a large selection of grit sizes.

There are, however, important differences between sandpaper intended for dry woodworking and waterproof abrasive paper designed for wet sanding.

Dry sandpaper

Ordinary dry sandpaper can be useful for shaping hardened filling materials, smoothing wooden substrates and working on preliminary foundation layers.

Its main advantage is convenience. It requires no water and is easily cut into small pieces.

However, depending on the abrasive and the material being worked, it can clog with sanding dust.

Wet-and-dry sandpaper

Waterproof abrasive paper is particularly useful for smoothing sufficiently hardened lacquer layers.

Using water helps carry away loosened particles and reduces clogging. It can also make the sanding action feel smoother and more controlled.

One familiar example is Matador waterproof abrasive paper, a long-established range often associated with fine wet sanding.

Other manufacturers produce similar waterproof silicon-carbide and aluminium-oxide papers.

A useful selection might include grits such as 400, 600, 800, 1000, 1500, 2000 and 3000, depending on the task.

The important thing is to choose a grit appropriate to the material and the amount that needs to be removed.

There is little benefit in using an extremely fine abrasive when a surface still needs substantial levelling.

Equally, using an unnecessarily coarse abrasive on a delicate lacquer layer can create scratches that take considerable work to remove.

2. Flexible Abrasive Sheets: Super Assilex and Similar Products

Modern abrasive technology offers some interesting alternatives to conventional sandpaper.

One example is Super Assilex, manufactured by the Japanese company Kovax.

Originally developed for demanding finishing applications, including automotive refinishing, these abrasive sheets are designed to produce a relatively uniform, shallow scratch pattern.

They have a flexible backing and are available in several grades.

Unlike conventional waterproof sandpaper, Super Assilex is primarily designed as a dry-sanding system.

For lacquerwork, its potential appeal is the combination of flexibility, controlled abrasion and a consistent finish.

It is worth remembering that the manufacturer's grit designations use the letter K, such as K800 or K1500. These should not automatically be treated as identical to conventional P800 or P1500 sandpaper.

Soft versus rigid backing

One of the most useful things about specialist abrasive sheets is that they can be combined with different backing pads.

A soft backing allows the abrasive to follow curved or irregular surfaces more readily.

A firmer backing is better suited to keeping a flat surface flat.

This distinction is particularly important in kintsugi, where a repair may cross both a curved ceramic surface and a raised line of hardened lacquer.

A very flexible abrasive can follow the raised repair rather than flatten it. A rigid backing may level the raised area more effectively, but requires greater care around adjacent surfaces.

Neither is automatically better. They simply serve different purposes.

3. Abrasive Stones and Whetstones

Abrasive stones are another option, particularly where a firm, flat sanding surface is desirable. They can also be cut or shaped to the size and form required for a particular task, making them useful for working on smaller or more intricate areas.

Japanese whetstones, commonly associated with sharpening knives and woodworking tools, can also be used in lacquerwork (e.g. Crystal Toishi).

Both natural and synthetic stones are available in different grades.

Their principal advantage is rigidity. A flat stone can help level raised areas without bending around them.

Small stones can also be shaped or selected to work on restricted areas.

However, a stone that is too coarse, too hard or unsuitable for the particular surface can cause damage.

Some synthetic stones release abrasive particles as they wear, while others remain relatively firm.

For beginners, small synthetic waterstones can be an accessible way to explore this type of abrasive without investing in expensive natural Japanese stones.

As with sandpaper, the correct choice depends on whether you are shaping a foundation, smoothing an intermediate lacquer layer or preparing a surface for further finishing.

4. Traditional Japanese Polishing Charcoal

Charcoal may seem an unusual abrasive to anyone unfamiliar with Japanese lacquerwork.

Yet specially prepared charcoal has a long history in traditional urushi finishing.

Different types are selected for their working properties and the stage of lacquerwork involved. Traditional polishing charcoal can also be surprisingly expensive.

Examples include:

• Hō-zumi (朴炭) — charcoal traditionally associated with magnolia wood, used in smoothing lacquer layers.

• Suruga-zumi (駿河炭) — used for fine abrasion and preparing lacquered surfaces.

• Roiro-zumi (呂色炭) — associated with fine finishing and high-gloss roiro work.

• Tsubaki-zumi (椿炭) — camellia charcoal, used in certain traditional polishing applications.

These materials are generally used with water and carefully controlled pressure.

They can be shaped to suit the work, making them useful for surfaces that would be awkward to approach with a large sheet of sandpaper.

Could ordinary barbecue charcoal work?

This is an interesting question, particularly because barbecue charcoal is inexpensive and widely available.

The answer is that ordinary barbecue charcoal is not necessarily equivalent to traditional polishing charcoal.

Commercial charcoal can vary considerably in its wood species, hardness, texture and impurities.

Charcoal briquettes are especially unsuitable as a direct substitute because they may contain binders, mineral additives or other ingredients.

Even natural lumpwood charcoal may have an inconsistent structure, with hard inclusions or fragile sections that crumble unexpectedly.

A carefully selected piece of clean, untreated lumpwood charcoal might be worth experimenting with on a disposable test surface, but I would not recommend assuming that any barbecue charcoal is suitable for valuable lacquerwork.

Traditional polishing charcoal is selected and prepared specifically for its abrasive characteristics.

5. Tokusa: Japanese Horsetail

Another fascinating traditional abrasive is tokusa (砥草), a type of horsetail plant, commonly associated with Equisetum hyemale.

Horsetail stems contain silica, giving their surfaces a naturally abrasive quality.

Historically, dried horsetail has been used in Japanese crafts for smoothing and polishing wood and other materials.

Unlike a conventional sheet of sandpaper, tokusa is a plant material.

Its stems can be prepared and used in small sections, making it an interesting option for certain delicate surfaces and detailed work.

Its abrasive action depends on the condition of the plant, its preparation and how it is applied.

It should not be thought of as having a precise modern sandpaper grit rating.

For someone interested in kintsugi, tokusa is worth knowing about even if modern abrasive papers are more convenient for everyday use.

6. Micro-Mesh and Cushioned Abrasives

Micro-Mesh is another useful category of fine abrasive.

Unlike ordinary sandpaper, many Micro-Mesh products use a flexible backing with a cushioning layer beneath the abrasive particles.

This allows the abrasive to conform to a surface and can produce a relatively even scratch pattern.

It is available in fine grades and is often used for polishing plastics, acrylics, metals and other finished surfaces.

For urushi work, its flexibility may be helpful when working on gentle curves or refining sufficiently hardened surfaces.

However, there is an important distinction between smoothing a surface and making it perfectly flat.

A cushioned abrasive tends to follow the shape beneath it.

If the goal is to remove a raised repair line, a rigid backing may be preferable.

Micro-Mesh also uses its own grading system, so its numbers should not be directly equated with ordinary sandpaper grit numbers.

7. Fine Abrasive Powders and Polishing Compounds

Not all abrasives come in sheets, blocks or stones.

Fine abrasive powders and polishing compounds have long played an important role in urushi finishing, particularly during the final stages of polishing.

Historically, traditional materials included:

· Tonoko (砥の粉) — a fine mineral powder used in certain traditional polishing preparations.

· Tsunoko (角粉) — finely prepared deer-antler powder traditionally used for fine polishing.

Although these materials remain part of the history of urushi craftsmanship, they are less commonly encountered in contemporary polishing practice, where modern manufactured abrasives offer greater consistency and convenience.

Today, alternatives include:

· Sanwa polishing powders — specialist Japanese abrasive powders available in different grades for fine finishing and polishing.

· Other specialist polishing powders and compounds — selected according to the desired finish and the surface being worked.

Depending on the technique, these abrasives may be used with water, oil or another suitable medium and applied using cloth, fingertips or specialised polishing materials.

Modern polishing compounds developed for automotive paint, plastics and other finished surfaces are also worth exploring, although they are not automatically suitable for every urushi finish (for example tableware).

Their formulations, abrasive particle sizes and cutting strengths can differ considerably.

For beginners, the important distinction is that fine polishing powders generally belong to the later stages of finishing. Unlike coarser abrasives used for levelling and shaping, their purpose is to refine an already prepared surface and progressively improve its appearance.

8. Why the Backing Material Matters as Much as the Abrasive

Abrasives are often discussed entirely in terms of grit numbers.

However, the backing material can make an enormous difference to how an abrasive behaves.

Consider three ways of using exactly the same piece of sandpaper.

Held loosely between the fingers: The paper can bend around curves and follow uneven surfaces.

Wrapped around a soft foam pad: The pressure becomes more evenly distributed while retaining some flexibility.

Wrapped tightly around a rigid block: The abrasive remains flatter, making it more suitable for levelling raised areas.

These arrangements can produce different results even though the abrasive grit is identical.

For kintsugi, this is especially useful because repairs often involve small, irregular areas rather than large, flat surfaces.

A narrow strip of abrasive attached to a small block may be more useful than a full sheet held loosely in the hand.

Similarly, a soft pad may be preferable when following the curve of a bowl.

It is worth experimenting with different backing materials before purchasing increasingly specialised abrasives.

9. Choosing an Abrasive for the Job

The choice of abrasive depends largely on the work being carried out and the surface you are trying to achieve.

For example, when working on a delicate kintsugi repair, you may want to avoid leaving visible scratches on the surrounding ceramic or glaze. Traditional polishing charcoal or tokusa may offer a gentler approach for certain finishing tasks, although neither is guaranteed to be completely scratch-free.

However, the result also depends on the technique and precision of the person carrying out the sanding. If you work carefully and keep the abrasive strictly within the area being sanded, ordinary sandpaper can do the job just as effectively without scratching the surrounding surface.

Where more material needs to be removed, wet-and-dry sandpaper may be more appropriate. It can be cut into narrow strips, folded into small sections or wrapped around a suitable backing to work precisely along a repair line without unnecessarily abrading the surrounding surface.

Other stages of urushi work may require more aggressive abrasives. For example, levelling ji-urushi ground layers or hardened sabi-urushi filling may involve removing considerably more material than refining a final lacquer coat. Coarser sandpaper, abrasive stones or rigid sanding blocks can therefore be more practical.

The shape of the object also matters. A flat surface may benefit from a rigid abrasive, while a curved bowl or an intricate repair may require something more flexible.

Ultimately, there is no single abrasive suitable for every task. The important thing is to choose a material that provides sufficient cutting action while allowing you to control exactly where and how much material is removed.

Final Thoughts

One of the enjoyable aspects of traditional Japanese craftsmanship is discovering how many different materials can accomplish what initially appears to be the same task.

Sandpaper is convenient and effective, but it is only one option.

Traditional polishing charcoal, horsetail, whetstones, fine powders and modern flexible abrasive sheets all offer different working characteristics.

You do not need to purchase every specialist abrasive to begin working with urushi.

A modest selection of waterproof sandpaper, together with a few simple backing blocks or pads, can cover many ordinary smoothing tasks.

As your experience develops, experimenting with other materials can help you discover which are most comfortable and effective for your particular work.

Ultimately, the most useful abrasive is not necessarily the most expensive or the finest, but the one that gives you the control required for the surface in front of you.

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