Our bonsai pot manufacturing techniques

At Bonsai Pot Manufacturing in Borbon, Philippines, in cooperation with Dot Pot Ceramics (Detlef Goroll, Germany), we primarily use four different techniques to create our handmade bonsai pots.

1. Slab Construction
We freely build angular pots from clay slabs, including rectangular, square, hexagonal, and octagonal shapes, as well as pots resembling natural rocks. This technique offers great design freedom and precise control over the shape.

2. Coil Construction
We use clay coils mainly to create primitive, unglazed round and oval pots, and occasionally rectangular ones. This method allows us to produce individual shapes with a rustic, natural character.

3. Plaster Moulds
Plaster moulds allow us to produce bonsai pots in almost any shape and achieve consistent dimensions, but we use them only rarely because we prefer more direct, hands-on construction methods.

4. Potter’s Wheel
Round and oval bonsai pots are formed on the potter’s wheel, a technique used predominantly by Detlef Goroll in Germany, which allows smooth contours, balanced proportions, and efficient shaping.

Our firing methods

Borbon, Philippines: We use our own gas-fired pottery kiln, which allows both Oxidation and Reduction firing, offering control over the firing atmosphere and enabling different clay colours and surface effects.

Germany: Our pots are fired in electric or wood-fired kilns; electric kilns offer precise temperature control and consistent results, while wood-fired kilns can create distinctive natural variations in colour, texture, and surface character.

Next, we'll go into a little more detail about each of these techniques

Techniques for making bonsai pots

Introduction

Bonsai pots are made using several traditional and modern pottery techniques. Each method offers different possibilities in terms of shape, size, surface texture, construction, and artistic expression. The choice of technique depends on the potter’s experience, the intended design, the type of clay, and the desired characteristics of the finished pot.

Four important methods are the use of plaster moulds, the use of clay coils, slab construction, and shaping on a potter’s wheel. Each technique has its own strengths and limitations, making it particularly suitable for certain forms of bonsai pots.

An important principle should be emphasised: the manufacturing technique does not directly determine the quality of a finished bonsai pot.

A pot made by hand from clay coils can be just as durable, refined, and aesthetically accomplished as one thrown on a potter’s wheel or formed in a plaster mould. Quality depends on the potter’s skill, the clay body, construction, drying, firing, and attention to detail.

1. Making pots from clay slabs

In slab construction, the potter rolls or presses clay into flat sheets. These slabs are cut to the required dimensions and assembled to form the base and walls of the pot. The joints are usually scored and joined with clay slip, then compressed and reinforced.

This method is particularly well suited to rectangular and angular bonsai pots, including designs with straight walls, pronounced corners, and carefully defined feet. It can also be used for hexagonal, octagonal, and other polygonal forms. Curved designs are possible, but they require more careful shaping of the slabs.

Advantages

• Excellent for geometric shapes: Straight walls, clean corners, and precise proportions are easier to achieve than with many other hand-building methods.
• Good control over dimensions: The potter can measure and cut each slab to establish the intended length, width, and height.
• Suitable for individual designs: Wall angles, rim profiles, feet, and decorative details can be varied freely.
• Efficient use of clay: Flat slabs can be cut economically from prepared sheets.
• Potential for a clean, architectural appearance: Carefully constructed slab-built pots can have a crisp and disciplined design.

Disadvantages

• Joints require careful execution: Poorly joined corners and bases can crack or weaken during drying and firing.
• Risk of warping: Large, thin, or unevenly dried slabs may bend or distort.
• Wall thickness must be controlled: Inconsistent thickness can lead to uneven shrinkage and structural problems.
• Curved forms are more challenging: Oval and rounded pots generally require additional shaping or alternative construction methods.
• Precision demands experience: Straight edges and symmetrical proportions require careful measuring, cutting, and finishing.

Slab construction is particularly suitable for rectangular bonsai pots and other geometric designs. It allows the potter to combine functional precision with a high degree of artistic freedom.

2. Making pots from clay coils

Coil construction is one of the oldest pottery techniques. The potter rolls clay into long, rope-like strands and builds the pot by placing them one above another. The coils are joined and compressed, and the walls are gradually shaped by hand.

For a round pot, the coils can be arranged in circular layers. By adjusting their placement, the potter can create different diameters, wall profiles, and rim shapes. A simple, rustic pot may retain some visible evidence of the construction method, while a refined pot can be smoothed until the coils are no longer visible.

Advantages

• Great freedom of form: The potter can create round, irregular, organic, or sculptural shapes without relying on a mould.
• Strong artistic individuality: Each pot can develop its own character through variations in contour, surface, and construction.
• Suitable for rustic designs: The technique lends itself particularly well to expressive, textured, and deliberately primitive-looking bonsai pots.
• No potter’s wheel required: Coil construction can be carried out with relatively simple tools.
• Flexible working process: The potter can gradually adjust the shape as the walls rise.

Disadvantages

• Time-consuming construction: Building and joining individual coils requires patience and careful attention.
• Risk of weak joints: Poorly compressed or inadequately joined coils may separate or crack during drying and firing.
• Difficulty maintaining uniform walls: Achieving consistent thickness and symmetry requires considerable practice.
• Potentially slower production: Producing several pots with identical dimensions can be difficult.
• Extensive finishing may be necessary: A smooth, highly refined surface requires additional work if the coils are not intended to remain visible.

Coil construction is especially suitable for handmade bonsai pots in which individuality, texture, and an organic appearance are important. Experienced potters can also use it to create highly refined pieces with precise proportions.

3. Making pots with a plaster mould

In this technique, a slab of clay is pressed into or over a plaster mould to create the desired shape. The mould determines the basic outline and dimensions of the pot. Depending on the design, the potter may add a separately formed base, feet, decorative elements, or a carefully finished rim.

Plaster absorbs moisture from the clay, helping it become firm enough to release from the mould while retaining its shape. After removal, the pot is refined by hand before drying and firing.

Advantages

• Consistent shapes and dimensions: Moulds make it easier to produce pots with similar proportions, which is useful for series production.
• Suitable for oval and rounded forms: Carefully designed moulds can produce smooth, flowing contours that are difficult to achieve consistently by other methods.
• Efficient production: Once a mould has been prepared, the forming process can be relatively quick.
• Reduced deformation during forming: The mould supports the clay while the basic shape is established.
• Repeatability: A potter can reproduce a particular design across several pots.

Disadvantages

• Limited design flexibility: The mould largely determines the shape, so substantial changes often require a new mould.
• Mould preparation takes time: Creating a suitable plaster mould requires additional work, space, and materials.
• Less individual variation: Pots made from the same mould may have a similar overall appearance, although hand-finishing can distinguish each piece.
• Risk of uneven wall thickness: Incorrectly pressing the clay into the mould can produce weak areas or inconsistent thickness.
• Release and drying problems: If the clay is too wet, too dry, or unevenly compressed, the pot may deform or crack.

Plaster-mould construction is particularly useful for potters who want to produce consistent oval or rounded bonsai pots while retaining the option of individual hand-finishing.

4. Making pots on a potter’s wheel

Wheel throwing involves placing a prepared lump of clay on a rotating wheel. The potter centres the clay and uses pressure from the hands to open it and raise the walls. The form is then shaped into a round vessel with the desired profile.

A round bonsai pot can be thrown directly on the wheel. Oval pots are more complicated because the wheel naturally produces circular forms. Depending on the method, an oval pot may be formed by reshaping a thrown vessel while the clay is still workable, by altering the form at a suitable stage of drying, or by using wheel-thrown components in a modified construction process.

After the initial shaping, the pot is allowed to firm up before its rim, base, feet, and other details are refined.

Advantages

• Natural rotational symmetry: The wheel is particularly effective for producing round pots with balanced proportions.
• Smooth surfaces and flowing contours: Experienced potters can create elegant profiles with relatively little subsequent smoothing.
• Efficient production of round forms: Once the technique is mastered, the basic forming process can be fast.
• Consistent wall thickness: Skilled throwing can produce walls that are relatively uniform.
• Strong potential for refined design: Subtle changes in curvature, rim shape, and wall profile can give a round pot considerable character.

Disadvantages

• A specialised skill is required: Centring clay and controlling the walls demands practice and coordination.
• Limited natural suitability for angular shapes: Rectangular and polygonal pots are not normally produced directly on the wheel.
• Size and weight limitations: Large pots can be physically demanding to throw and difficult to handle safely.
• Oval shapes require additional work: Transforming a circular vessel into an oval one can cause distortion or uneven wall thickness if performed incorrectly.
• Equipment and workspace are necessary: A potter’s wheel requires investment, maintenance, and adequate working space.

Wheel throwing is an excellent choice for round bonsai pots, particularly when smooth contours and balanced proportions are desired. Oval pots can also be produced, but they often require additional shaping and careful control beyond the initial throwing process.

5. Comparison of the 4 techniques

Technique	Particularly suitable for	Main advantage	Main limitation
Plaster mould	Oval and rounded pots, repeatable designs	Consistency and efficient forming	Shape depends largely on the mould
Clay coils	Rustic, organic, round, and individual designs	Great freedom of expression	Joining and wall thickness require care
Clay slabs	Rectangular and polygonal pots	Precision and geometric control	Corners and joints can be vulnerable
Potter’s wheel	Round pots and modified oval forms	Smooth contours and rotational symmetry	Limited direct suitability for angular forms

These categories are not absolute. A skilled potter can combine techniques, use moulds only for part of a pot, or modify a basic shape by hand. Hybrid methods can offer advantages that a single technique cannot provide on its own.

6. Does the technique determine the quality ?

The answer is no. The manufacturing technique alone is not a reliable indicator of quality.

A plaster-moulded pot can be carefully finished, structurally sound, and aesthetically exceptional. A coil-built pot can display extraordinary craftsmanship and subtle proportions. A slab-built pot can achieve precise geometry and excellent durability, while a wheel-thrown pot can demonstrate remarkable control of form and surface.

Conversely, every technique can produce inferior results when the work is poorly executed. Uneven walls, weak joints, distorted proportions, inadequate drainage, unsuitable clay, careless drying, or incorrect firing can compromise a pot regardless of how it was formed.

When evaluating a bonsai pot, it is therefore more useful to consider the following criteria:

• Proportions and design: Does the shape complement the tree’s species, trunk, foliage, and overall style ?
• Construction: Are the walls, base, corners, and feet sufficiently strong and properly finished ?
• Functionality: Does the pot provide adequate drainage and suitable space for the root system ?
• Clay and firing: Is the material appropriate for its intended use, and has the pot been fired correctly ?
• Craftsmanship: Are the rim, surface, feet, and other details executed with care ?
• Aesthetic character: Does the colour, texture, finish, and overall form work harmoniously with the bonsai ?

A handmade pot may also possess distinctive artistic qualities that are not easily reproduced in mass production. However, these qualities arise from the potter’s design, decisions, and execution rather than automatically from a particular forming method.

Conclusion

Plaster moulds, clay coils, clay slabs, and the potter’s wheel each provide different ways of transforming clay into bonsai pots. Moulds favour repeatability, coils encourage organic expression, slabs offer precision in geometric designs, and wheel throwing excels at round forms and smooth contours.

The best technique is the one that suits the intended design and enables the potter to achieve the desired combination of appearance, function, and durability.

Ultimately, the quality of a bonsai pot is determined by the skill and care with which it is designed, constructed, dried, and fired - not by the technique used to shape the clay.