Unleashing The Power Of Hot Pot Kilns: A Comprehensive Guide

Using a hot pot kiln for the first time can be intimidating, but with the right preparation, it becomes a rewarding experience. Here's a step-by-step guide to help you get started:

Step 1: Prepare Your Kiln

- Ensure your kiln is free of any debris or dust that could impact the firing process.

- Vacuum the kiln, paying special attention to the coils and the kiln lid if it's a top-loading model.

- Perform a safety inspection: check for loose or missing hardware, and ensure no electrical cords or flammable materials are nearby.

- Test your kiln's ventilation system.

Step 2: Load Your Kiln

- Position kiln shelves and furniture strategically, allowing for airflow and staggering heights.

- Never fire wet clay—this can be dangerous and lead to kiln damage or injury.

- Maintain clearances: keep at least 2 inches from the kiln lid and thermocouple, and 1 inch from the kiln floor and walls.

Step 3: Program Your Kiln

- Set the desired temperature and timer based on the clay type and other factors.

- For manual kilns, slowly increase the temperature over several hours.

- For electric kilns with programmable controls, choose a suitable program.

Step 4: Unload Your Kiln

- Wait for the kiln temperature to drop below 125°F (50°C) or to room temperature before opening.

- Remove kiln shelves and cones, wearing loose clothing and heat-resistant gloves.

- Inspect the cones for any signs of deformation, indicating potential issues with the kiln's performance.

Step 5: Update Your Firing Log

- Record details about the firing process, including kiln furniture arrangement, cone ratings, and any issues observed.

- This log will help you improve your results over time and identify potential problems early on.

Prepare your kiln

Before you start using a kiln, it's important to take some preparatory steps to ensure a successful firing process and protect your creations from defects. Here are the steps to properly prepare your kiln:

Clean the Kiln: Over time, small amounts of brick dust, clay particles, and glaze residue can accumulate inside the kiln. Even when the kiln is not in use, dust and debris can settle inside. This can lead to reduced efficiency, higher costs, and the development of hotspots, which can shorten the lifespan of the coils and cause them to burn out prematurely. Therefore, it is essential to thoroughly clean the kiln before each use. Use a vacuum to remove dust and debris, paying special attention to the coils and the kiln lid if it is a top-loading kiln.

Perform a Safety Inspection: Safety should be a top priority when working with a kiln. Inspect the kiln for any loose or missing hardware, including screws, nuts, and bolts. Thermal expansion during firing can cause these to work loose, so tight and secure hardware is crucial. Ensure that electrical cords and flammable materials are not touching or too close to the kiln. Keep the area around the kiln clear of debris, as even the outside of the kiln can get hot enough to cause spontaneous combustion. Check the area above the kiln to ensure that heat-activated fire alarms or sprinklers are not present, as the heat from the kiln could accidentally activate them. Additionally, make sure your ventilation system is functioning properly to remove toxic fumes and heavy metals produced during firing.

Run a Test Firing: Before loading your kiln with ceramics or pottery, it is recommended to perform a test firing to identify any hidden problems. Load the kiln with shelves and any other kiln furniture you plan to use. Place a 04 Self-Supporting Witness Cone on each shelf, approximately two inches from the kiln wall, and one next to the thermocouple. Set the kiln for a low fire cycle, similar to light bisque firings (Cone 04-06). For manual kilns, slowly increase the temperature over several hours. For electric kilns with programmable controls, choose a medium-speed 04 ConeFire program. Ensure that the flue is properly set if your kiln has a downdraft vent. Seal the lid and turn on the kiln, noting the start time to calculate the total firing time. Listen for the clicking of the relays in the control box as they energize and shut off power to the heating elements. Observe the temperature reading, which should gradually increase and then slow down as it approaches the target temperature. If the relays stick or the temperature continues to climb, turn off the kiln and call a service technician. Allow the kiln to complete the firing process and cool down naturally before opening.

Inspect the Kiln Furniture and Cones: Once the kiln has cooled down, open the lid and remove the kiln shelves and cones. Wear loose-fitting clothing and heat-resistant gloves, as the kiln furniture can retain a lot of heat. Inspect the kiln furniture and cones closely. Cracked shelves can indicate the presence of hotspots within the kiln. The cones should be bent by about twenty degrees or slightly more but should not be leaning against the shelves or still standing straight. Overly bent cones indicate an overheating issue, while cones that are only slightly deformed or unchanged suggest a dead zone in the kiln due to burned-out heating elements or a worn-out relay. In either case, consult a service technician for assistance.

Load your kiln

Loading a kiln properly is essential to ensure the success of your firing. Here are some detailed instructions on how to load your kiln:

Prepare the Kiln

Before loading, check the kiln floor for any cracks, debris, glaze drips, or other issues. If the floor is in good condition, apply a coating of kiln wash, but avoid doing this if there are electrical elements embedded in the floor. If your kiln has a vent system port or burner port, ensure that no kiln wash gets into those areas. Check the kiln shelves and ensure they are clean, free of cracks, and well kiln-washed, especially for glaze and test firings.

Set Up the Bottom Shelf

Place posts for the bottom layer of shelving. If your kiln does not have heat coming from below, you can use one-inch posts. If your kiln has a floor element, ventilation port, or floor burner, it is recommended to use two-inch posts. The bottom shelf should be at least 1/2" and no more than 1" up from the kiln floor. If there is an element in the kiln floor, position the bottom shelf right under the bottom-most side element.

Stack the Pottery

When loading the kiln, always distribute the weight straight downward. Unsupported clay under pressure is likely to crack. Place the pottery on the shelves, with taller items in the centre and shorter items on the edges. This allows radiant heat to reach the ware in the centre of the shelf. Leave adequate space between the items to prevent them from touching, as this can affect the glaze and final product. For glazed ware, leave at least 1/4" of space between pieces. For greenware pieces to be bisqued, it is acceptable for them to touch. When viewing the kiln from the top, ensure that nothing is sticking out over the edges of the shelves.

Shelf Placement and Spacing

As you stack the kiln, maintain proper shelf spacing. The next shelf above the bottom shelf should be a minimum of 8" higher (7" if there is an element in the kiln floor). Lower shelves near the bottom will cause the kiln to fire slower. As you approach the top of the kiln, return to a greater distance between shelves, with at least 8" between the topmost shelf and the lid when it is closed. Place posts 3-4 inches in from the edge of the shelves, and use at least three posts per shelf to prevent wobbling. For heavier loads, use additional posts, especially on the bottom. Always stack the posts directly above each other from top to bottom.

Safety Precautions

Never load wet ware into the kiln. Maintain clearances of 2" from the lid, 1" from the kiln walls, at least 1" from the bottom, and 2" from any thermocouples. Large flat surfaces should be angled away from the elements and thermocouples to prevent overheating. Leave a space of at least 1/2" between the tallest piece and the kiln lid when closed.

Program your kiln

Programming your kiln can be intimidating at first, but it won't take long before it becomes second nature. Here are some tips for programming your kiln:

Understand the Controller

The controller controls the power of the kiln by reading the temperature in the kiln chamber with a thermocouple, which then relays the temperature information to the controller. The controller then decides whether to send power to the elements or not. If it decides to send power, it sends a signal to the relays to close (connecting the power) and power is sent to the elements.

Firing Programs

Firing programs were developed because bad things can happen to your art if you go too fast or too slow through certain temperature ranges. Most hobbyists use factory programs that address these issues. Sometimes, you may want to fire something that your controller's preset programs are not designed for, and therefore you need to write your own programs. For example, if you wanted to fuse glass in a kiln that is only equipped with factory programs for ceramics. Most controllers used by hobbyists have a programming mode called Ramp and Hold, where you would enter your program.

ConeFire Mode

In ceramics, the factory programs are accessed through ConeFire Mode, which can be found on most ceramic controllers offered through kiln manufacturers. To load a ConeFire program, enter a preheat time, the cone value you want to fire to, and a hold time at peak temperature if desired. The preheat is entered in hours and minutes (e.g. 1 hour and 45 minutes). A preheat time is recommended if you are unsure if the piece is completely dry. If you place a ceramic piece, especially a large or thick piece, in the kiln that still has moisture in it and fire it too fast, the water left wants to escape as steam and can crack your piece. When you enter a preheat time, the program brings up the temperature very slowly and holds it at the time you have entered below boiling point (usually around 180 F). When the preheat time expires, the kiln moves on to the next segment of the program.

The Cone Value

The cone value you enter can be for a bisque (unglazed clay) firing or a glaze firing. Each clay and glaze has a cone value listed on the box or jar that the manufacturer recommends firing to. Simply enter that recommended cone value and press enter.

Firing Speed

The firing speed is determined by whether you are doing a bisque fire or a glaze fire. Slow is recommended for bisque fires since there may still be moisture in the piece. Medium is recommended for glaze firings, and Fast is only used for specialty items like decals.

Hold Time

Your hold time is generally used to balance out the temperature in the kiln to make sure all of the pieces receive the same amount of heat work. Usually, a 5-minute hold is recommended to achieve this. You can also add a little more hold time if you want to increase the total amount of heat work if your cones were not bending enough.

Unload your kiln

When it comes to unloading your kiln, patience is a virtue. It can be exciting to open the kiln after a glaze firing, but it's important to wait until the kiln has cooled below 125°F before opening the lid. Opening it too soon can cause the glaze to craze, and it will no longer be food safe as bacteria can grow in the small cracks.

As you unload the kiln, make notes in your firing log about the cones, how the kiln was loaded, the appearance of the ware, and the duration of the firing. This will help you make adjustments for your next firing.

After unloading, there are several chores associated with kiln maintenance. These include cleaning the kiln shelves of wadding and ash residue, gathering and splitting wood, removing ash from the firebox, and making any necessary kiln repairs or modifications.

It's also important to properly dispose of any waste generated during the unloading and cleaning process, such as old wadding and ash. This waste can be hazardous, so be sure to follow the appropriate guidelines for disposal.

Additionally, be sure to inspect your kiln for any damage or issues that may have occurred during the firing process. This includes checking the elements, thermocouple, and other components to ensure they are in good working condition. If you notice any problems, be sure to address them before using the kiln again.

Overall, unloading your kiln requires patience and attention to detail. By following the proper procedures and maintaining your kiln, you can ensure the best results for your creations and the longevity of your kiln.

Update your firing log

A firing log is an essential tool for anyone using a kiln regularly. It is a way to learn about your kiln and recall the specifics of your firing process. Over time, a well-kept log becomes critical to keeping track of your work and helps you avoid making the same mistakes twice.

There are many reasons to keep a kiln log, from the practical to the whimsical. It is a place to record the specifics of your firing process, from the clay to the glaze, and everything in between. It is also a place to record your experiments and their outcomes, both good and bad.

• Record the date, number of firings, type of firing (bisque, glaze, luster, or other), the program used, the contents of the kiln, and any other relevant notes.
• Include blank pages for your favourite firing schedules, glaze combinations you want to try, and shapes of pieces you'd like to make.
• Record the firing schedule used, the temperatures reached, and any holds or slow cools.
• Keep a list of standard schedules and any adjustments made over time.
• Make note of which glaze-firing combinations have been successful and which ones haven't worked so well.
• Record the number of firings done to keep track of how many times the kiln has been used since the last time the elements were changed.
• Record any changes to your firing schedule, such as adding hold time or skipping steps, and whether these changes gave you the desired results.
• Take pictures and make sketches to include in your log.
• Keep your log in your work area, and enter information after each firing.

Keeping a kiln log may seem tedious, but it is a priceless tool that will help you learn and improve your craft.

Frequently asked questions