Fact No. 342. (Published on 1/13/2006)


Heat, which is defined as the transfer of thermal energy between things, is an important ingredient in many glass art methods. Understanding the different types of heat can help the lampworker, fuser or glass blower to better recognize how different heating processes work.

The three forms of heat most important to the glass artist are:

Ambient Heat (also "convection"): The transfer of thermal energy from the surrounding area (typically the air).

Radiant Heat: The transfer of thermal energy that results from direct radiation.

Conductive Heat: The transfer of thermal energy that results when two objects (that are different temperatures) come in contact with each other.

Okay, so what does that all mean? Let me illustrate, Texas style:

It is a hot Texas day. Hotter than a stolen tamale. And even though you are sitting under a nice, shady Pecan tree you're still so hot you figure if you were a chicken you'd be laying hard-boiled eggs. That's ambient heat you're feeling. It comes from the warmth in the air around you.

You stand and take a few steps towards your F150 Extended Cab pickup (with the bumper sticker that says "Texas is Bigger than France" on it) because you're fixin' to get yerself a seven course meal (a dead possum and six pack) out of the ice chest. You step out from under the shade. Suddenly it feels a whole lot hotter. Hotter than a honeymoon hotel. That's the radiant heat of the sun you are feeling.

Overwhelmed by all this heat, you stagger and only keep from falling by grabbing the fence. Next thing you know your jumping around like a long-tail cat in a room full of rocking chairs. And you realize that burned bq you smell is your hand sizzling on the galvanized steel fence. That would be conductive heat.

So, why does this matter to a glass artist? Here is an example:

Dark glass absorbs more radiant heat than lightly colored glass. This can result in an increased risk of thermal shock to a glass design that combines dark and light colors. Since the source for radiant heat in a kiln are the glowing elements, shielding the glass from radiant heat can improve the evenness of heating.

Movement of air, proximity to elements, and the inclusions of metals within glass all impact the transfer of heat. Understanding the type of heat you are dealing with can help to solve problems and improve technique.

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