A Simple Guide To Bisque Firing

A Simple Guide To Bisque Firing

In this article, we will take you through the basics of bisque firing, so you can successfully complete your first bisque fire.

 

What is bisque firing?

Ceramic pieces typically undergo two firings:

1. Bisque Firing

2. Glaze Firing

Bisque firing is the first firing, which converts bone-dry, fragile clay into a more durable and porous ceramic material. During bisque firing (also known as biscuit firing), the clay is heated at a controlled pace and is then allowed to cool slowly.

The clay is then ready to be decorated with underglaze, glaze or other decorations, before it is fired again.

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Bisque Firing Basics

Before we go on, we will clear up some of the common terminology relating to bisque firing:


Bisque or Biscuit Firing: This is the initial firing process aimed at making ceramic ware robust enough for decoration

Candling: A gentle heating technique where the kiln and its contents are warmed slightly above ambient temperature but kept below water's boiling point.

Single Firing: Firing ceramic ware just once to achieve a finished product.

Sintering: A process that strengthens a ceramic piece by heating it until its materials coalesce, through solid-phase reactions or melting, resulting in significant bonding without necessarily changing volume.

Twice Firing: Involves initially firing the ceramic ware, then applying and firing glazes to achieve a completed or intermediate product.

Why do you need to bisque fire?

Bisque firing is a fundamental process in ceramics. It is essential to transform the initially fragile clay body into something more robust and porous. 

1. Strengthening the Clay Body

The initial transformation that occurs during bisque firing is the strengthening of the clay.

By subjecting the clay to a controlled heating process, bisque firing hardens the material, making it more resilient to handling and further processing. 

This increased durability is essential for applying decorative elements, underglazes, and glazes without compromising the structural integrity of the piece.

2. Creating a Porous Surface

One of the unique outcomes of bisque firing is the creation of a porous surface on the clay body.

This is crucial for the glazing process, as it allows the clay to absorb glazes and underglazes better. The porosity allows the glaze to bond well to the surface, leading to a more uniform and stable finish after the final glaze firing.

3. Eliminating Moisture and Impurities

Bisque firing also removes residual moisture and organic impurities trapped within the clay. The controlled heating process allows moisture to evaporate gradually, preventing cracks and explosions that can occur if the clay is heated too rapidly.

Additionally, bisque firing burns away organic materials and gases, ensuring that the clay is chemically stable and ready for glazing.

5. Facilitating Safe Glaze Application

The bisque firing process not only prepares the clay body for glazing but also makes the application of glazes safer and more efficient.

The strength and porosity achieved through bisque firing allow for even glaze application, reducing the likelihood of glaze running or pooling during the final firing.

This level of control is essential for achieving intricate designs and consistent finishes in ceramic art.

How to Succesfully Bisque Fire

Here are the steps that you need to take to ensure your bisque firing goes to plan!

1. Prepare Your Pieces

Dry Your Work Thoroughly: Before bisque firing, ensure that your ceramic pieces are completely dry. Any residual moisture can lead to cracks or explosions in the kiln. Allow pieces to air dry slowly and evenly to prevent warping or cracking.

Inspect and Clean: Check each piece for any surface debris or imperfections. Gently clean the surfaces with a soft brush or sponge to remove dust that could affect the firing process.

2. Load the Kiln

Shelf Placement: Start by positioning the bottom shelf at least 1 inch above the kiln floor to enhance air circulation. Use kiln posts to achieve this spacing.

Arrange Pieces Carefully: Place ceramics on the kiln shelves, ensuring they are not touching each other or the kiln walls. This spacing allows for even heat distribution and prevents damage.

Remember to leave space between taller pieces and the top shelf or kiln lid to avoid any contact during firing.

Optimize Loading: For efficiency and energy conservation, load the kiln as fully as possible without overcrowding. Proper airflow between pieces will allow uniform heating.

Bisque Firing Schedules

Here, we will go through what temperatures you should fire your kiln to when bisque firing. The bisque fire temperature is a key aspect.

Key Temperatures for Bisque Firing (UK)

Bisque Firing Temperature: The temperature range for bisque firing typically falls between cone 06 (around 999°C) and cone 04 (about 1060°C). This range is suitable for most types of clay, including earthenware and stoneware.

Bisque Firing Temperature for Earthenware: Specifically for earthenware, aim for the lower end of the bisque firing range (cone 06). This temperature effectively removes water and organic material from the clay, making it porous and perfect for glazing.

Bisque Firing Temperature for Stoneware: For stoneware, aim for a bisque firing temperature around cone 5 to 6, which translates to approximately 2167°F to 2232°F (1186°C to 1222°C).

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The Firing Ramp

Initial Heating (Candling): Begin with a low-temperature preheat phase (candling) to ensure all remaining moisture is removed. This stage is particularly important for thicker pieces.

Ramp Up Temperature Gradually:

Increase the temperature slowly to prevent cracks or explosions. A general guideline is to start with a rate of 55-111°C per hour until reaching 538°C, then adjust according to the specific requirements of your clay body and kiln.

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Bisque Firing Pottery Tips

1. Always ensure your pottery is completely dry before loading it into the kiln to prevent explosions.

2. Place a cone pack inside your kiln to monitor the actual temperature and make adjustments as needed.

3. Keep a log of your firings to refine your process over time, noting the specific schedule and outcomes for each batch.

Reading a Bisque Firing Chart

A bisque firing chart provides a visual guide to the temperatures and times needed for the firing process. It usually includes:

Ramp Speed: How quickly the kiln should increase in temperature, usually expressed in degrees per hour.

Target Temperature: The specific temperature you need to reach for your type of clay.

Hold/Soak Time: The length of time the kiln stays at the target temperature to ensure even heat distribution throughout the pottery.

There is probably information about the recommended firing schedule for your specific clay on the manufacturer or retailer's website.

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As always, if you have any other questions pelase reach out to us at info@thepotterypeople.co.uk!


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