The most common types are electric, gas, and wood-fired kilns. Electric kilns are popular for their ease of use and precise temperature control. Gas kilns, often fueled by propane or natural gas, offer a broader range of atmospheric effects but require more expertise. Wood-fired kilns provide unique textures and colors due to ash deposits and flame paths but are labor-intensive and less predictable. Each type has its own set of advantages and disadvantages, and the choice often depends on the potter’s needs, expertise, and desired results.
What A Kiln Is And What It Is Used For?
Definition of a Kiln
What is a Kiln?
A kiln is a specialized furnace designed to reach high temperatures and is used for firing materials like ceramics, glass, and metal.
Primary Uses of a Kiln
Ceramics
- Firing Clay: Hardens and matures clay bodies.
- Glaze Curing: Helps the glaze material adhere to the ceramic piece, creating a glass-like surface.
Glasswork
- Annealing: Slowly cools hot glass to relieve internal stresses.
- Fusing: Melts different pieces of glass together.
Metallurgy
- Smelting: Extracts metal from its ore.
- Heat Treatment: Alters the properties of metal.
Different Types Of Kilns
Electric Kilns
- Purpose: Popular among hobbyists and schools due to ease of use, consistent results, low cost, and low emissions.
- Design: Generally cylindrical and top-loading.
- Temperature: Can reach between 1828°F and 2345°F.
- Elements: Usually only have elements in the side walls for better heat distribution.
Ceramic Kilns
- Size: Range from small countertop units to the size of a refrigerator.
- Temperature: Fired between 1828°F and 2345°F.
- Materials: Designed to withstand high temperatures and harsh environments.
- Design: Elements are generally in the side walls to support multiple levels of ware.
Glass Kilns
- Purpose: Used to fully melt glass for blowing into shapes or for annealing.
- Temperature: Rarely fired over 1700°F.
- Elements: Can have elements in the lid for even heat distribution.
- Design: Various shapes and sizes, including large oval or rectangular designs.
Metal Clay Kilns
- Size: Usually small table-top models due to the expense of the material.
- Temperature: Generally rated up to around 1800°F.
- Design: Can be top or front-loading units.
Specialized Kilns
- Bronze and Copper: Require a small crucible kiln filled with material that burns to create a reduction atmosphere.
Types of Kilns Pros and Cons
Electric Kilns
- Ease of Use: Simple to operate and offer precise temperature control.
Pros
- Suitable for beginners.
- Energy-efficient.
Cons
- Limited in creating atmospheric effects.
- May require a dedicated electrical circuit.
Gas Kilns
- Atmospheric Effects: Capable of creating a range of effects due to the combustion process.
Pros
- Versatile in terms of firing atmosphere.
- Can reach higher temperatures.
Cons
- Requires more expertise to operate.
- May require special ventilation.
Wood-Fired Kilns
- Unique Effects: Ash deposits and flame paths create unique textures and colors.
Pros
- Produces one-of-a-kind pieces.
- Traditional and rustic appeal.
Cons
- Labor-intensive.
- Less predictable outcomes.
Types of Materials That Can Be Fired in a Kiln
Kilns are versatile pieces of equipment that can fire a range of materials, each with its own specific firing temperature and characteristics. Whether you’re working with different types of clay, ceramics, or various metals, understanding the properties and requirements of each material is crucial for successful firing.
Clay
Earthenware
- Temperature: Fires at lower temperatures, usually around 1745°F to 2012°F.
- Characteristics: Porous and not as strong as other types of clay.
Stoneware
- Temperature: Fires at higher temperatures, between 2150°F and 2330°F.
- Characteristics: Non-porous when fired and very durable.
Porcelain
- Temperature: Fires at very high temperatures, usually above 2300°F.
- Characteristics: Translucent and extremely durable.
Ceramics
Glazed Ceramics
- Temperature: Varies depending on the glaze, usually between 1828°F and 2345°F.
- Characteristics: Glass-like surface after firing.
Bisque Ceramics
- Temperature: Lower than glazed ceramics, usually around 1832°F.
- Characteristics: Porous surface, often fired again with a glaze.
Metal Products
Metal Clay
- Temperature: Generally rated up to around 1800°F.
- Characteristics: Used for small jewelry items.
Bronze and Copper
- Special Kilns: Require a crucible kiln filled with material that burns to create a reduction atmosphere.
- Temperature: Varies, but usually high temperatures are needed.
Iron and Steel
- Temperature: Extremely high, often exceeding 2500°F.
- Characteristics: Used in industrial settings, not typically for art or hobby work.
Tips for Choosing the Right Type of Kiln
Choosing the right kiln involves multiple factors including the scale of your projects, the materials you’ll be using, and your level of expertise. Budget considerations and safety are also crucial. By carefully evaluating your specific needs and options, you can select the kiln that’s just right for you.
Assess Your Needs
Project Size
- Small Projects: For jewelry or small ceramic pieces, a table-top electric or metal clay kiln may suffice.
- Large Projects: For bigger ceramic or sculpture work, consider a larger gas or electric kiln.
Scale of Production
- Hobbyists: A small to medium electric kiln is usually adequate.
- Large-Scale Manufacturing: Industrial kilns with higher capacities and automated features are essential.
Consider Material Requirements
Clay Types
- Earthenware: Lower temperature kilns are sufficient.
- Stoneware and Porcelain: Require kilns that can reach higher temperatures.
Other Materials
- Glass: Choose a kiln with elements in the lid for even heat distribution.
- Metals: Specialized kilns like crucible kilns may be necessary for metals like bronze and copper.
Evaluate Features
Temperature Control
- Manual: Suitable for experienced users who want to control every aspect of the firing.
- Automated: Ideal for beginners or those who prefer consistent, repeatable results.
Atmosphere
- Oxidation: Electric kilns are generally better for oxidation atmospheres.
- Reduction: Gas kilns offer more flexibility for reduction firing.
Budget and Operating Costs
Initial Cost
- Low Budget: Open-air or Raku kilns are generally cheaper.
- High Budget: Automated kilns come with a higher price tag.
Operating Costs
- Electricity vs. Gas: Electric kilns may have higher operating costs depending on local electricity rates.
- Maintenance: Gas and wood-fired kilns may require more frequent maintenance.
Safety and Ventilation
- Ventilation: Ensure proper ventilation, especially for gas kilns.
- Safety Features: Look for kilns with safety shut-offs and other safety features.
Types of Firing Available in Kilns
The type of firing you choose will depend on various factors including the material you’re working with, the effects you’re aiming for, and your level of expertise. Each firing type has its own set of advantages and disadvantages, and understanding these can help you make an informed decision.
Direct Firing
Definition
In direct firing, the material being fired is in direct contact with the combustion gases.
Characteristics
- Immediate Heat Transfer: Quick and efficient heat transfer.
- Oxidation: More likely to produce an oxidation atmosphere.
Pros
- Faster heating and cooling cycles.
- More efficient fuel usage.
Cons
- Risk of contamination from combustion gases.
- Less control over firing atmosphere.
Indirect Firing
Definition
In indirect firing, the material is isolated from the combustion gases, usually by a barrier or secondary chamber.
Characteristics
- Controlled Atmosphere: Allows for a more controlled firing atmosphere.
- Slow Heat Transfer: Heat is transferred more slowly compared to direct firing.
Pros
- Reduced risk of contamination.
- Better control over firing atmosphere.
Cons
- Slower heating and cooling cycles.
- Less efficient fuel usage.
Raku Firing
Definition
A type of direct firing often used in Japanese Raku pottery, involving rapid heating and cooling.
Characteristics
- Quick Firing: Extremely fast heating and cooling cycles.
- Post-Firing Reduction: Pieces are often placed in a reduction atmosphere after firing.
Pros
- Unique and unpredictable results.
- Quick firing cycles.
Cons
- Requires close monitoring.
- Limited to smaller pieces.
Salt and Soda Firing
Definition
A variation of direct firing where salt or soda is introduced into the kiln at high temperatures.
Characteristics
- Chemical Interaction: The salt or soda reacts with the clay to form a glaze.
- High Temperatures: Usually fired at stoneware temperatures.
Pros
- Unique glaze effects.
- Can be used in gas or wood-fired kilns.
Cons
- Corrosive to kiln materials.
- Requires specialized knowledge.
How to Maintain and Operate a Kiln
Maintaining and operating a kiln requires regular cleaning, periodic checks, and adherence to safety protocols. Proper maintenance not only ensures the longevity of your kiln but also guarantees that it operates efficiently and safely.
Regular Maintenance
Cleaning
- Interior: Regularly vacuum the interior to remove dust and debris.
- Shelves: Clean kiln shelves after each firing to remove glaze drips.
Lubrication
- Hinges and Latches: Periodically lubricate with high-temperature grease.
- Mechanical Parts: Check for wear and tear and lubricate as needed.
Operational Checks
Element Inspection
- Visual Check: Look for broken or worn-out elements.
- Resistance Test: Use a multimeter to check the resistance of the elements.
Thermocouples
- Calibration: Ensure thermocouples are calibrated for accurate temperature readings.
- Replacement: Replace if they show signs of wear or inaccuracy.
Safety Precautions
Ventilation
- Proper Venting: Ensure the kiln is properly vented to the outside.
- Fume Extraction: Use a fume hood or extractor fan if necessary.
Protective Gear
- Heat-Resistant Gloves: Always use when loading or unloading the kiln.
- Safety Goggles: Protect your eyes from heat and dust.
Fire Safety
- Fire Extinguisher: Keep a suitable fire extinguisher nearby.
- No Flammable Materials: Ensure no flammable materials are near the kiln.
Energy Efficiency
Firing Schedule
- Batch Firing: Try to fire the kiln when it’s full to make the most of the energy used.
- Off-Peak Hours: Use the kiln during off-peak energy hours if possible.
Insulation
- Check Seals: Ensure the door and any openings are well-sealed.
- Insulation Bricks: Check for wear and replace if needed.
Differences Between Electric and Gas Kilns
Electric and gas kilns differ in their energy sources, temperature ranges, firing atmospheres, and costs. Electric kilns are generally smaller, easier to use, and safer, making them popular among hobbyists and educational institutions. Gas kilns offer more control over the firing atmosphere and are often used for larger, industrial applications.
Energy Source
Electric Kilns
- Source: Powered by electricity.
- Connection: Requires a dedicated electrical circuit.
Gas Kilns
- Source: Powered by propane or natural gas.
- Connection: Requires a gas line or propane tank.
Temperature Range
Electric Kilns
- Range: Generally up to 2345°F.
- Consistency: More consistent temperature throughout the kiln.
Gas Kilns
- Range: Can reach higher temperatures.
- Consistency: May have temperature variations within the kiln.
Firing Atmosphere
Electric Kilns
- Oxidation: Primarily an oxidation atmosphere.
- Control: Less control over the atmosphere.
Gas Kilns
- Oxidation and Reduction: Can achieve both oxidation and reduction atmospheres.
- Control: More control over the firing atmosphere.
Size and Capacity
Electric Kilns
- Size: Generally smaller, suitable for hobbyists and small studios.
- Capacity: Limited by electrical circuit capacity.
Gas Kilns
- Size: Available in larger sizes, suitable for industrial use.
- Capacity: Can handle larger volumes of work.
Cost and Efficiency
Electric Kilns
- Initial Cost: Generally less expensive to purchase.
- Operating Cost: May be more expensive depending on local electricity rates.
Gas Kilns
- Initial Cost: More expensive upfront.
- Operating Cost: May be cheaper to operate depending on local gas prices.
Safety and Ventilation
Electric Kilns
- Ventilation: Requires less ventilation than gas kilns.
- Safety: Generally considered safer due to the absence of combustible gas.
Gas Kilns
- Ventilation: Requires good ventilation to remove combustion gases.
- Safety: Requires careful monitoring to prevent gas leaks and explosions.
How a Natural Gas UPDRAFT Kiln Works
A natural gas updraft kiln works by utilizing natural gas as its fuel source, igniting it in a combustion chamber at the bottom and allowing the heat to rise naturally through the kiln. It offers several advantages such as fuel efficiency, atmosphere control, and high-temperature capabilities, making it a versatile choice for various applications.
Basic Functioning
Combustion Chamber
- Location: Located at the bottom of the kiln.
- Function: Natural gas is mixed with air and ignited here.
Flue System
- Location: Positioned at the top of the kiln.
- Function: Allows hot gases and combustion by-products to exit.
Airflow
- Direction: Air flows upward, hence the term “updraft.”
- Mechanism: Natural convection or forced air moves heat from the bottom to the top.
Firing Process
- Ignition: Natural gas is ignited in the combustion chamber.
- Heat Circulation: The heat rises naturally through the kiln, warming the pottery.
- Exhaust: Combustion gases and excess heat are vented out through the flue system at the top.
Temperature Control
- Gas Flow: Regulated to control the internal temperature.
- Air Supply: Adjusted to achieve the desired oxidation or reduction atmosphere.
Advantages Over Other Types of Kilns
Fuel Efficiency
- High BTU: Natural gas has a high BTU, making it a very efficient fuel source.
Atmosphere Control
- Oxidation and Reduction: Easier to control the firing atmosphere compared to electric kilns.
High-Temperature Capability
- Range: Can reach higher temperatures suitable for stoneware and porcelain.
Scalability
- Size: Can be built to a large scale, making it suitable for industrial applications.
Lower Operating Costs
- Fuel Cost: Natural gas is generally cheaper than electricity, leading to lower operating costs.
Versatility
- Material Range: Suitable for a wide range of materials, including various types of clay and glazes.
What is a Kiln Sitter?
A Kiln Sitter is an essential tool in pottery kilns for ensuring accurate and safe firing conditions. It automates the process, allowing for consistent results and freeing up the potter’s time. Its versatility also makes it suitable for various types of pottery projects.
Definition
A Kiln Sitter is a mechanical device used in pottery kilns to accurately measure and control the temperature and firing time.
Components
Sensing Rod
- Material: Made of pyrometric cones or metal.
- Function: Melts or bends at a specific temperature.
Trigger Mechanism
- Location: Connected to the sensing rod.
- Function: Releases a switch to turn off the kiln when the desired temperature is reached.
Timer
- Type: Manual or digital.
- Function: Sets the maximum firing time as a backup to the sensing rod.
How It Works
- Setup: A pyrometric cone or metal rod is placed in the Kiln Sitter.
- Firing: The kiln is turned on and begins to heat up.
- Temperature Sensing: The sensing rod bends or melts at the target temperature.
- Trigger: The bending or melting action triggers the mechanism to shut off the kiln.
- Timer Backup: If the sensing rod fails, the timer will turn off the kiln after the set time.
Importance in Pottery Kilns
Accurate Firing
- Temperature Control: Ensures that the kiln reaches the desired temperature for the specific clay or glaze.
Safety
- Automatic Shutoff: Turns off the kiln when the target temperature is reached, preventing over-firing and potential hazards.
Consistency
- Repeatable Results: Provides consistent firing conditions, which is crucial for producing uniform pottery.
Time-Saving
- Unattended Firing: Allows for unattended firing, freeing up time for other tasks.
Versatility
- Multiple Projects: Can be adjusted for different types of clay and glazes, making it versatile for various projects.
Measuring the Capacity of a Kiln
Measuring the capacity of a kiln involves calculating the internal volume using its dimensions or the area and number of kiln shelves. Knowing the capacity is crucial for efficient firing, energy savings, and project planning.
Definition of Capacity
The capacity of a kiln refers to the amount of space available for firing objects. It is usually measured in cubic feet or liters.
Methods for Measuring Capacity
Internal Dimensions
- Height, Width, Depth: Measure the internal dimensions of the kiln chamber.
- Formula: Capacity (cubic feet)=Height (ft)×Width (ft)×Depth (ft)Capacity (cubic feet)=Height (ft)×Width (ft)×Depth (ft)
Using Kiln Shelves
- Shelf Area: Measure the area of one kiln shelf.
- Number of Shelves: Count the number of shelves that can fit in the kiln.
- Formula: Capacity (cubic feet)=Shelf Area (sq ft)×Number of ShelvesCapacity (cubic feet)=Shelf Area (sq ft)×Number of Shelves
Manufacturer’s Specifications
- Catalog or Manual: Refer to the manufacturer’s specifications for the kiln’s capacity.
Factors Affecting Effective Capacity
Object Size and Shape
- Irregular Shapes: Oddly shaped objects may reduce the effective capacity.
Air Circulation
- Spacing: Adequate space between objects is necessary for even heating.
Firing Requirements
- Temperature and Atmosphere: Different projects may require different firing conditions, affecting how much can be fired at once.
Importance of Knowing Capacity
Efficient Firing
- Batch Firing: Knowing the capacity helps in planning batch firing, making the process more efficient.
Energy Savings
- Optimal Use: Firing a near-capacity kiln is generally more energy-efficient than firing a partially filled one.
Project Planning
- Scheduling: Helps in scheduling multiple projects and meeting deadlines.
FAQ: Types of Kilns
What are the 3 main types of kilns?
The three main types of kilns are electric kilns, gas kilns, and wood-fired kilns. Electric kilns are powered by electricity and are generally easier to use. Gas kilns use natural gas or propane as fuel and offer more control over the firing atmosphere. Wood-fired kilns use wood as fuel and are often used for specialized, artistic projects.
What is a kiln that is loaded from the top called?
A kiln that is loaded from the top is commonly referred to as a “top-loading” kiln or “top hat” kiln.
What is the difference between an electric kiln and a gas kiln?
Electric kilns are powered by electricity and are generally easier to use and maintain. They offer more consistent temperatures but are limited in the types of atmospheres they can create. Gas kilns use natural gas or propane and offer more control over the firing atmosphere. They can also reach higher temperatures.
What are the different types of modern kilns?
Modern kilns include electric kilns, gas kilns, wood-fired kilns, and specialized types like soda kilns, salt kilns, and raku kilns. There are also industrial kilns designed for mass production.
What materials can be fired in pottery kilns?
Materials that can be fired in pottery kilns include various types of clay, ceramics, porcelain, and some metals.
Are there any benefits to using simple ‘pit’ kilns instead of modern ones?
Pit kilns are simpler and cheaper to construct. They are suitable for low-fire ceramics and can be a good option for educational or experimental projects. However, they offer less control over temperature and atmosphere.
What temperature range must be maintained for optimal results when firing in a kiln?
The optimal temperature range depends on the material being fired and the desired end result. For earthenware, temperatures around 1745°F to 2012°F are common. For stoneware, it’s around 2192°F to 2372°F, and for porcelain, it’s up to 2552°F.
What are the advantages and disadvantages of front-loading kilns compared to top hat kilns?
Advantages: Front-loading kilns are easier to load and unload, especially for larger pieces. They often have better insulation and heat distribution.
Disadvantages: They can be more expensive and may require more space.
Can all materials be fired in both top hat and front-loading kilns or are some more suited to one type than the other?
Most materials can be fired in both types of kilns. However, large or irregularly shaped pieces may be easier to fire in front-loading kilns.
Are there any safety precautions that should always be taken when working with electric or gas-powered kilns?
Always ensure proper ventilation, keep flammable materials away from the kiln, and use heat-resistant gloves and safety goggles. For gas kilns, regularly check for gas leaks and ensure proper combustion air supply.
How do you measure the capacity of a kiln?
Kiln capacity is usually measured in cubic feet or liters, calculated based on its internal dimensions or the area and number of kiln shelves.
How often should a kiln be maintained?
Regular maintenance, including checking elements, thermocouples, and the general condition of the kiln, should be performed at least once every few months or after a set number of firings.
