Why New Potters Struggle with Trimming: The 10 Overlooked Steps and Skills Every Beginner Misses

Trimming is an auxiliary process in the ceramic forming technique, inevitably leaving unique marks on the surface of the ware. Since all wares need further refinement after their initial shaping, trimming has been around since the birth of ancient pottery. Early trimming tools were likely made of stone, wood, and pottery, used to roll, pat, or smooth the surface of the wares. Impressed pottery, painted pottery, and Longshan black pottery produced in primitive societies were created this way.

The trimming technique became a leading process in the forming technique during the Kangxi, Yongzheng, and Qianlong periods of the Qing Dynasty in Jingdezhen, leading to the saying, "three parts shaping, seven parts trimming." This development is closely related to the introduction of steel files.

Types of Trimming: Dry Trimming vs. Wet Trimming

Trimming can be divided into two types: dry trimming and wet trimming. The choice between them depends on the dry strength of the clay body. For clay bodies with generally higher dry strength, wet trimming is often used, controlling the moisture content at around 15%. For those with lower dry strength, dry trimming is preferred, with moisture content controlled below 10%.

Dry trimming leaves shallow marks, making them lighter; wet trimming involves deeper cuts, leaving heavier marks. The outer edge of the foot ring is sharper with dry trimming, while it tends to be rounder with wet trimming.

When to Start Trimming?

Once a vessel shaped on the wheel reaches a semi-dry state, it can be placed back on the wheel, usually upside down to center it, and then the excess clay is trimmed away to enhance the form of the piece.

Key Actions in Trimming

1. Remove the excess parts from the body using a trimming tool or knife, scraping along the surface or edges to achieve the appropriate thickness and smoothness inside and out.
2. Use a curved knife to refine the inside of the body to meet shape requirements.
3. Trim the bottom of the body to ensure it is flat and free of excess clay.
4. Use a flat knife to smooth and even out the rim of the body.

Common Oversights for Beginners in Trimming:

1. Maintain the stability of the clay body to avoid deformation or damage.
2. Keep the center of gravity in mind to ensure the body doesn't tilt or collapse during trimming.
3. Choose and maintain tools carefully, keeping them sharp and flat for efficient and precise trimming.
4. If cracks or other defects are found during trimming, take immediate action to repair or adjust.
5. Perform a quality check after trimming to ensure the body meets requirements. Unqualified pieces should be re-trimmed or discarded.

Preventing Cracks During Trimming:

1. Control the moisture content of the body to prevent cracks due to too much or too little water.
2. Allow the body to naturally dry and harden before trimming to reduce internal stress and the risk of cracking.
3. Be mindful of the force applied during trimming to avoid excessive pressure that could cause surface cracks.
4. Use appropriate lubricants or coolants to reduce friction between the tool and the body, preventing surface cracks.
5. Ensure tools are sharp and flat to avoid surface damage.
6. Keep the environment clean to prevent damage or contamination of the body's surface, affecting its strength and stability.
7. For areas prone to cracking, such as edges or thin walls, special treatments like adding support or thickening may be used to enhance strength and stability.

The Importance of Tools in Trimming 

In discussing the importance of tools in the trimming process, we specifically recommend beginners to use flat tungsten steel knives for trimming.

Why use tungsten steel trimming knives for pottery? Tungsten steel is preferred for its exceptional hardness and wear resistance, offering durability, precision, versatility, and stability. These qualities make tungsten steel knives ideal for achieving detailed craftsmanship and efficient work.

Why use flat knives for pottery trimming? Flat blade knives, especially those made of tungsten steel, offer a wide surface area for efficient smoothing and leveling, flexibility in application, control and precision, and improved safety. These features make flat blade knives suitable for both beginners and professionals in pottery trimming.

In conclusion, to deepen your understanding of the trimming process, don't miss out on Florian's insightful tutorial videos on pottery trimming. Watching these will undoubtedly boost your confidence and skill in this intricate craft.