Kiln Secrets

" Getting to know the types of units...and what to purchase!"

A glass kiln is an oven used for the glass fusing techniques.

This is the most expensive item of all the fusing supplies.

They come in a variety of sizes and shapes.

If you are looking to purchase a kiln, check out the great table top units at Delphi Glass - Art Glass Tools & Supplies.

These are fantastic for fusing at home as they run on your household current.

They are usually lined with fire brick, which maintains the heat, and can support the objects being heated.

The size is an important factor, because it limits the quantity and size of items that can be fired at one time.

There are many parts to this heating unit.

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Long ago, objects were fired in an open fire.

The heat could not be measured or regulate, and the effects of a direct flame made it unmanageable.

Over time, it was found that if objects were fired in an enclosed space, like a brick oven, you could achieve a higher degree of heat, and a slower cooling of objects.

Glass has seen a rebirth in the past few years.

It is used as a building material, a surface to paint on, engraved, cut, blown, slumped and fused.

Before purchasing, figure out the size that will fit your individual firing needs, whether you want a manual or a programmable unit , and find out what type of warranty comes with this appliance.

Ask where and how you will get repairs done. What parts of the unit are replaceable and where you can purchase these parts.

Once the unit has been purchased, get to know your firing kiln .

This will come in handy in any future firings.

Glass vs Ceramic

Glass ovens heat single layers from the top, while ceramic units heat multiple layers from the side.

Most glass projects are relatively flat, and with the heat radiating from the top, the entire face of the glass receives heat at the same time.

This helps to keep the temperature differences within the glass uniform and helps to prevent cracking.

You can still obtain these uniform heating results in a ceramic oven by slowing down the firing.

An electric unit is the best for working with glass.

The temperature can be regulated and controlled.

They are also quiet, safe to operate, easy to handle, and fairly inexpensive to operate.

There are numerous types of electric units on the market, in a variety of sizes and accessories.

These ovens are usually insulated, so there is very minimum external heat, and with no or very little fire hazard.

What Size to Purchase

Make a decision on how large the items are that you are going to make, that will help you decide the size to purchase.

Find out the internal dimensions and external dimensions you need for the size of your desired projects.

If you are going to use larger molds, will you have to fire on the bottom of the unit?

You need at least 12 inches clearance around the outside, so figure out where you are going to place it and make sure it will fit in this area.

Front load vs Top load

A front loading firing kiln is great if you are going to be removing items from the unit while they are hot.

This is great if you are planning on doing any enameling.

A top loading kiln has either a hinged lid or one that can be lifted off with handles and removed completely.

This is most commonly used for glass fusing.

Electrical Outlets

Know your electrical outlets.

If you are glass fusing at home, then you will want a kiln that uses standard 120 volt, 13 amp household current.

You don’t want to have to do any rewiring to your home.

It should have a three-prong plug and about an eight foot power cord.

Manual or Programmable


A manual oven has an on/off switch and a dial to adjust the temperature.

There is small light to show that the unit is on and operating.

They come with a pyrometer so the inside temperature is shown at all times.


thermocouple runs from the pyrometer into the oven.

It should protrude into the firing chamber about one inch.

Remember, the pyrometer will read the temperature where the tip of the thermocouple wire is, so put it near your shelf.

These are not that difficult to use and don’t require that much more time or effort than a programmable unit .

Keep records of your firing.

At first, set your timer for every 15 minutes, so you can see the rate of temperature for your particular unit.

Keep records of the particular rates of temperature climb with each digit on your dial.

Records will help you determine what works and what doesn’t work with each firing.

Make detailed records of the total time it took from the start of your firing, to when you reached your desired temperature.

These records will help you in future firings.

Then in the future, you can set your alarm to go off just before you know your oven should be at a particular temperature, instead of having to check it every 15 minutes or so.

Always unplug your kiln when you are finished firing.

Be sure to set an alarm clock to remind you when switches should be changed.

An automatic kiln has a temperature controller , digital controller, or a kiln sitter.

It fires automatically and turns off the kiln after your firing is complete.

The digital controller is programmable and you can set different programs for different types of fusing.

They are reliable and simple to use.

You can set it to start at any time you desire.

You can also set it to heat to certain temperatures, or hold at a desired temperature.

Brick or Ceramic Fiber

Firebricks are used as insulation in a brick oven.

They heat more quickly and retain heat longer.

These are great for glass fusing and annealing.

More maintenance is needed because of the delicate nature of the fire bricks.

The heating coils are placed in grooves in the fire bricks.

If these coils should ever bulge out, they must be pushed back into place.

Read more about fixing these coils here .

A ceramic fiber oven stays clean and is easier to maintain.

The heating elements of these units are not exposed, because they are molded into the walls.

Kiln Safety

Even though a kiln will fire to a higher temperature than a stove, the area around the unit is surprisingly cool during firing.

Glass kilns are well built and don't radiate a lot of area heat.

For safety purposes, the unit should not be placed within a minimum of 12 to 18 inches of any other object.

It is recommended that the unit be placed on a flame retardant flooring.

Some place the kiln on a stand on a flame resistant cement floor or fire board.

Be careful when opening the lid while the unit is at a high temperature.

The heat will escape and rise.

If you have low ceilings, cabinets, shelves, or other objects close by the heat will hit these items and could start a fire.

Always use common sense on what you have near or around the kiln.

Be aware of where the heat goes when opening the lid during firing.

If opening the lid while doing procedures like raking, etc. always unplug the unit before proceeding with the process.

Make sure that the power circuits are up to supplying the kiln.

If there is a question about the supply, have an electrician check things out.


The furniture consists of a shelf and shelf supports.

These items are made of a highly refractory fire clay.

The shelf material is quite strong, and should fit your particular unit.

There should be about 1 inch of clearance between the shelf and the wall of the oven.

Furniture is inexpensive, easily available, and can be used over and over again.

The shelf needs to be protected with either a wash, or fiber paper.

Care and Maintenance

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When you first make your purchase, keep all the packaging material.

If the unit needs to be sent back for repairs or replacement, you will be happy that you kept the original box and packaging materials.

You first need to prepare the kiln and shelf for firing.

Then you will be ready for a first firing of a fused glass project.

Use the shelf and posts.

Having your items on these shelves allows air to circulate around your item and makes it easier to remove the shelf from the kiln.

Place the shelf at least one inch below the thermocouple when firing.

Use protection on your oven and shelf.

The unit needs to be coated with a wash.

When coating the unit, it doesn't matter which wash you apply, just be sure to mix it about twice as thick as you would if you were using it to coat the shelves.

Avoid getting any wash on the elements .

Reapply the wash every few years or as needed.

The shelf can be protected with either a wash or fiber paper.

Repairing coils might seem like a tedious task.

See how simply this can be done without having to send your unit out for repair.

Periodically check and clean your thermocouple.

This can be done using a damp cloth before firing your piece.

Also check the position each time you start to fire.

Try to avoid hitting the thermocouple with the kiln shelf, as it can be broken and damaged.

Check for any dust on the floor of your unit.

Vacuum if necessary.

Dust can react with the color elements in your glass and result in foggy or burnt colors.

For a small and inexpensive oven, try purchasing a microwave unit.

These are very limited in use and applications.

Technical Terms

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