Fixing those annoying cold spots in glassware annealing
If you’ve ever worked with glass that has a weird shape—think long necks, chunky handles, or those tricky tapered bases—you know the struggle. You put it in a standard kiln, everything looks fine, but you still end up with “dead zones.” The problem is that air is lazy. In a convection kiln, the heat just doesn’t want to crawl into tight cavities or wrap itself perfectly around a curve. You’re left with cold spots, and that’s where the stress builds up. Here is how we handle it: we stop relying on air and start using short-wave IR lamps. Hitting the hard-to-reach spots IR radiation doesn’t drift around like hot air; it moves in straight lines and hits the glass directly. It’s like a spotlight for heat. We set these lamps up in a multi-angle array, basically flooding the inside of the piece with energy from every direction. It’s the only way to make sure the whole thing hits the annealing point at the same time, so you don’t have to worry about the glass cracking later. The gear we use We usually go with high-wattage quartz halogen tubes. You need a lot of power density here. If you’re running a 230V or 400V system, you get a response that’s almost instant. You can tweak the temperature on the fly without waiting forever for the kiln to “catch up.” The quartz shell is the secret sauce—it lets the filament get screaming hot without burning out. And we use R7s or SK15 connectors. Why? Because when a lamp eventually pops on the shop floor, you just swap it out. No rewiring, no downtime, no headache. The catch: Don’t overdo it Now, a word of warning: IR is aggressive. Because the heat is so direct, it’s easy to accidentally “hot spot” your glass if the lamp is too close or stays on too long. It happens fast. To keep things under control, we pair the lamps with an IR pyrometer and a closed-loop PID controller. This keeps the glass from accidentally hitting its softening point while you’re just trying to kill a dead zone. At the end of the day, it’s all about the spacing. Get the distance right, and you get a perfectly flat thermal profile across the whole piece. Simple as that.