How To Candle Clay Vessels

The act of candling your clay vessel can be an easy task if done properly and safely. This article will explain what exactly candling is and how to use it effectively for a successful firing.

What Is Candling?

Candling is the process of breaking down the H2O chemical bond by bringing the dried clay vessels temperature into waters boiling range. This effectively cooks out all of the chemically bonded water in the vessel before it ever touches a flame. Candling is a crucial step and must be done for a successful firing.

Types Of Candling

There are two types of candling that will be discussed in this article. One is a modern technique that uses modern technology, and one is a primitive technique using only fire as a means to candle.

– Modern

This technique is easy and straightforward, it only requires patience and the appliance itself. To do this modern style of candling, you will need an oven. Yes, that’s correct. All you need is an oven. Don’t be afraid of putting your pottery in the oven, this will do no damage to your clay vessel or your kitchen appliance as long as your oven reads temperature accurately.

The first step is to set the racks in your oven so that your clay vessels are equal distance from the top and bottom, or as close as you can get it. Some of your clay pieces may skew more towards the top of your oven, and that’s okay.

After placing your rack in the right position, begin putting your clay vessels onto the rack. Make sure that the oven is not on at this point. Do not slide your pieces onto the rack as this can cause marks on your bone dry vessels. You can use a tray or something else thats flat to set your vessels on if you do not want to put them directly onto the rack.

Once the vessels are in close the door of the oven fully and set the temperature to 190 degrees fahrenheit. Be sure not to get your clay vessels past 212 degrees fahrenheit as this is the boiling temperature for water. At boiling temperature your clay vessels could explode. This is due to the water rapidly expanding into a gas with no where to go. Candling breaks down H2O’s atmospheric and chemical bond in the clay slowly, which then evaporates from the clay vessels so that exploding does not occur.

If any of your vessels crack or explode during this phase while you have the temperature set to 190, you may need to adjust your temperature by bringing it down 20 to 30 degrees. If that still does not fix the issue, you may have a bad temperature sensor or your heating element may be faulty.

Keep your clay vessels in the oven for 2 hours at 190 degrees to ensure that your pieces have had enough time to candle and dissipate all remaining moisture. While this helps with atmospheric water in the clay vessel, you may still have the chemical H2O bond in your piece. The chemical bond requires a higher temperature to fully break down and dissipate all remaining H2O. If you have a very thick piece you have to make sure you candle for a longer duration of time than you would with wall thickness of 1/4″ or less. Thicker walls means it will take longer for the heat to hit the core of those walls and in turn the longer it will take for that H2O to convert to steam and escape the walls.

– Primitive

The primitive technique for candling your pots has been used for thousands of years and is still a reliable way of making sure that your firing is a successful one. Primitive candling is the act of using radiant heat from an open flame to candle your pots. This can be done with a small fire or a bon fire depending on how many pieces you have and their size.

The perfect setup for candling your clay vessels would be to have a fire pit with walls to help hold in and reflect radiant heat back to the vessels being candled. In the picture below, the granite stone helps to not only keep the fire in, but also absorb and reflect radiant heat back to the pots. This ensures more of an even and consistent heating.

When you place your pots down make sure that they are not too close to the primary heat source, as this can cause them to crack. The cracking can occur because one side of your pot may be far higher in temperature than the side that is not facing the heat source. The disparity in temperature from one side to the other can create thermal shock and inevitably crack the pot.

To find the perfect spot to place your clay vessel, make sure that it is facing the heat source with the most surface area as possible. If your piece is flat, prop a stone or broken pottery underneath it to so that more surface area hits the vessel. After setting up the spot, gauge the temperature of radiant heat hitting your pot with a simple test. Place your hand in between the heat source and your clay vessel, the back of your hand should face towards the heat source. If you can keep your hand between your pot and the heat source for over 5 seconds, your pot should probably be closer to the fire. Anywhere from 3-5 seconds should be the max time your hand should stay there before it becomes uncomfortable.

Remember to periodically spin or flip your pieces so that all sides of your clay vessel can catch that radiant heat and candle properly. As the fire begins to turn to coal you can open up this coal bed and place your pieces into the middle so that they can heat more evenly in preparation for your firing. Make sure to wear all protective gear when moving your pots and logs at this stage. Log tongs and welding gloves are the most suitable for this stage. Do not attempt without the right protective gear and equipment.

As your pots begin to heat more, you should slowly start pushing the logs closer and closer to your pots. Do this in 20-30 minute intervals, inching the logs into a closer and more compact circle on each interval. Eventually the wood should be within 1/2″ to an inch and your pots should be taking the full brunt of radiant heat.

After you’ve noticed your pots/sculptures/vessels are starting to turn black or darker in color, then you are ready for firing. The absorption of carbon is a good sign that your pots are up to temp and ready to be on direct flame and coal.

Remember to take your time and be careful with this process, if you rush these steps you could end up with a bunch of pottery sherds instead.

How To Candle Clay Vessels