Dealing with those annoying cold spots in your glass annealing
If you’ve spent any time with annealing kilns, you know the frustration of “cold spots.” It’s a nightmare. You’ve got a complex piece—maybe a narrow-neck flask or a beaker with a deep base—and the standard heating elements just can’t get into the tight spots. The result? Uneven stress. And we all know where that leads: shattered glass. To stop the cracking, we’ve been using gold-coated shortwave infrared lamps. Here is why they actually work. The secret is in the gold Most quartz lamps throw out a broad spectrum of energy, but a lot of that just bounces right off the glass. It’s wasted. By adding a thin layer of gold to the quartz envelope, we shift the emission spectrum. Instead of bouncing around, the heat is concentrated into wavelengths that the glass actually wants to absorb. It turns the lamp into a directional heat beam. It doesn’t just warm the surface; it pushes the heat deep into the center of the vessel. Getting the power right To get your glass up to temperature quickly, you need the right specs. We usually go with high wattage and precise voltage. Why? Because the kiln chassis itself acts like a giant heat sink, sucking energy away. You need a punchy, high-wattage tube to fight that. Just a heads-up: make sure you’re using high-temp leads for the wiring. And be careful. If you cram too much wattage into a tiny space, you’ll fry the lamp ends. It’s all a balancing act between your power density and how fast your conveyor is moving. Making it work on the floor Think of these lamps as “gap fillers.” You don’t rely on the general air in the kiln to do the heavy lifting. Instead, you point these lamps exactly where the dead zones are. Now, there is a catch. Gold isn’t cheap, so it’s an investment. You also have to be obsessive about cleanliness. A little bit of dust or a fingerprint of oil on that gold surface creates a hot spot on the quartz. That’s a one-way ticket to a blown tube. When you’re installing them, treat it like a clean-room job. Keep the grime away, and the lamps will last.