Fixing Those Annoying Cold Spots in Your Glass Kilns
If you’ve ever pulled a complex piece of glassware out of the kiln only to find it cracked, you know the frustration. It usually happens because of “dead zones”—those stubborn spots where the heat just doesn’t reach. Traditional convection or resistance heating is great, but it has limits. It can’t always get into the tight nooks and crannies, leaving you with internal stress and a lot of wasted work. That’s where medium-wave IR lamps come in. Instead of relying on hot air to drift around, these lamps shoot heat directly into the glass. Why medium-wave? Here is the thing: different wavelengths behave differently. Short-wave lamps often just bounce off the surface. Long-wave heaters don’t have enough “oomph.” But medium-wave? It hits the sweet spot for silica. It’s like a floodlight for heat. Since the energy travels in a straight line from the filament to the glass, you can actually aim it. You can point the lamps right at those recessed angles or narrow necks that air currents usually ignore. Getting the setup right We usually go with quartz envelopes for these lamps. They can handle the intense heat you need for annealing without breaking a sweat. Depending on how much room you have in your kiln, you can wire them in series or parallel to get the wattage just right. But a word of advice: match the lamp length to the height of your piece. There is no point in paying to heat air that isn’t touching your glass. And be careful with high-wattage tubes. They speed things up, sure, but they hit your power supply with a massive surge the moment they kick on. If your power supply is cheap or under-specced, you’ll burn through filaments way faster than you should. The catch Nothing is perfect. While these lamps kill off dead zones, they create very intense, localized heat. If you put a lamp too close to a thin wall, you might scorch the surface while the core is still freezing. It’s a delicate balance. The trick is to give the lamps some breathing room and use PID controllers to ramp the temperature up slowly. It takes a bit of patience, but it stops the glass from shocking and ensures the whole piece hits the annealing point together.