Do You Need a Kiln for Glass Blowing? What Does It Do?

Surprisingly, the basic method of blowing glass has changed little since the practice first became widespread in the days of the Roman Empire.

The techniques and tools used today are, in fact, quite similar to what was used centuries ago. 

It’s amazing that ancient craftsmen were able to grasp the complexities involved with working with molten glass and to develop and perfect the art of glass blowing without the help of the internet, electricity, and modern appliances. 

Today, glass artists have access to modern furnaces with carefully monitored internal temperatures, but it’s important to understand which furnaces are used for which purposes.

Do you need a kiln for glass blowing? A kiln, or annealer, is required when glass blowing to relieve stresses in the glass incurred during the forming process by bringing the piece to a uniform temperature. The kiln then cools the glass at a predetermined rate to increase future durability and prevent breakage.

Glass blowing requires creativity, the ability to tolerate hot working conditions, and dexterity on the part of the glass blower, but there are several pieces of equipment that are required as well. 

Let’s explore what function a kiln serves in the glass-blowing process and why exactly it is so critical in forming a sturdy glass-blown object.

What Is a Kiln Used for in Glass Blowing?

A kiln is the third furnace used by glass blowers to ensure that the glass is properly annealed and cooled. 

Using some form of a kiln is absolutely necessary to prevent the glass from breaking while being cooled and to relieve the stresses caused by the glass-blowing process.

It seems odd that a kiln, which reaches very high temperatures is a necessary tool to bring down the temperature of the glass, but it is indeed a critical piece of equipment that helps eliminate the risk of thermal shock.

Confusing Terms

Glass blowers refer to the final furnace in the process as an annealer, not a kiln. However, the annealer is simply a temperature-controlled, programmable kiln. 

You may hear of the annealer being referred to as a lehr, though technically that is a different machine, but by far, annealer is the most widely used term in the world of glass blowing.

On the other hand, various other crafts that involve working with melted glass, such as lampworking, glass slumping, glass fusing, and glass casting, refer to the furnace simply as a kiln.

Additional names for the kiln include an annealing oven, an annealing furnace, cooling furnace, and an annealing kiln.

Whatever name is used, the purpose is the same – to safely cool the glass, eliminate stresses, and ensure long-term durability of the glass.

Why Is Annealing Necessary?

In order to understand why annealing is critical, it’s important to realize what the glass endures during the glass-blowing process. 

The Basic Glass-Blowing Process

First, the solid glass mix is melted in the crucible of the large, first furnace at roughly 2,000℉.

The glass blower then uses the blowpipe to dip out a glob of molten glass to be shaped and blown. 

While the glass is being formed and worked, the glass blower frequently inserts the glass into a glory hole, which is the second furnace in the lineup. 

This is done to reheat the glass to around 1,500℉, hot enough to keep it soft and malleable.

This frequent reheating means that the glass is still incredibly hot by the time the glass blower is satisfied with the creation. Usually, it is between 1,400 and 1,500℉.

How the Glass Is Affected

You may recall from science class that glass expands when heated and contracts when cooled.

During glass blowing, the glass is subjected to numerous changes in temperature, which causes internal stresses. 

Also, by the time the glass is ready to be set aside for cooling, some portions will be hotter than others, and the outer portion of the glass will begin to cool long before the inner core will.

This provides additional stress and will result in cracked or shattered glass if not rectified.

It is crucial to get every area of the glass to about the same temperature before a controlled cooling can begin. This is where the annealer comes into play.

What the Annealer Does

The annealer, or kiln, can be programmed to bring the entire thickness of the glass to a certain temperature, called the annealing point. 

The annealing point is the temperature at which the glass is cool enough to hold a solid shape, but hot enough to not cause additional contracting and stress.

For most glass, the annealing point is typically just under 1,000℉, and the glass must be held at precisely that temperature for an average of one hour per every ¼ inch of thickness. 

This holding period is called an annealing soak. The soak gives all areas of the glass sufficient time to reach the same temperature. 

Once this has been accomplished, the temperature will be lowered incrementally at a predetermined rate over a period of 12 hours or so, longer for thicker pieces.

Glass is usually left in the annealer until it has reached room temperature, at which point it may be safely removed. 

This entire process is known as annealing, and regardless if it is done in an annealer or a kiln, it is a crucial final step when blowing glass.  

What Happens If You Don’t Anneal the Glass?

Glass that has not been annealed is at risk of breaking at the slightest change in temperature or gentlest of bumps.

Non-annealed glass may even shatter spontaneously without a visible cause.

No Annealer? Here’s What to Do

For true glass blowing, a professional annealer is really the only way to go.

Annealers can be used for both large and small items, something that is not true of most kilns, and they can hold several items at once, again, not possible with small kilns.

The issue with an annealer is, of course, space. Remember, the annealer is the third furnace used when blowing glass. 

If you are interested in setting up your own glass-blowing area, you’re going to need a lot of space, not only for the three furnaces but for maneuvering room and all the other tools as well. 

I explain more about the possibility of setting up a home-based studio in this article, but for most people, this is not a viable option.

There are, however, several other avenues available to you that will allow you to pursue the hobby at a much more reasonable cost.

Take Classes 

Many universities and glass-blowing facilities offer classes that will allow you to learn the craft under the direction of experts.

All of the equipment needed will be available to you, and you’ll be learning from the best of the best.

Some facilities, once you’ve mastered the basics, will allow you to become a member for a nominal fee with access to everything you need to continue in the craft.

Learn Lampworking

Lampworking is an offshoot of true glass blowing but on a much smaller scale, small enough that you could easily set up a workspace at home. 

Lampworking, also called flameworking and torchworking, uses a torch as a heat source to melt solid glass to the point of being workable. 

The melted glass is then shaped, blown, or manipulated much in the same way as glass blowing.

Marbles, beads, figurines, ornaments, jewelry, and other small objects are possible with this technique. 

The huge advantage to learning this form of glass work is that a small kiln can be used for annealing the finished glass object. 

Glass kilns are most commonly used, but many ceramic kilns designed for use with clay can be used to anneal as well. 

What’s the Difference Between Glass and Ceramic Kilns?

Glass kilns typically heat from the top, and ceramic kilns heat from the sides. 

As long as the kiln is electric, large enough for the projects that you have in mind, and features a programmable controller for annealing cycles, it should be suitable for annealing small glass items.

Look for models which feature a ramp/hold setting and are equipped with a pyrometer and thermocouples to accurately monitor temperature.