How to Kill “Cold Spots” in Your Glassware
If you’ve ever worked with glassware that has a weird shape—think narrow necks or deep pockets—you know the nightmare of “cold spots.” Standard convection ovens just can’t get the heat into those tight corners. The air misses the mark, the glass stays unevenly stressed, and then—crack—you’ve got a fracture on your hands. It’s frustrating and expensive. To fix this, we stop relying on hot air and start using shortwave infrared (SWIR) heating arrays. Getting the heat where it actually belongs Air heating is slow. Infrared is different because the energy hits the glass surface directly. We use shortwave emitters because they pack a punch—they have higher energy density and can actually sink deeper into the material. The trick is in the setup. We don’t just put one lamp in the middle; we arrange them in a multi-angle array around the conveyor or nip rollers. This lets us hit the piece from every possible direction. No more “shadows” caused by the shape of the bottle or jar. The gear we use We usually go with high-wattage quartz halogen tubes. They run hot, which is exactly what we want, because it shifts the light spectrum to those shorter wavelengths that heat things up fast. Plus, we can build these to whatever length fits your specific kiln. Maintenance shouldn’t be a headache, so we stick with standard R7s or SK15 connectors. If a lamp goes, you just swap it out and keep moving. We also use quartz glass envelopes so the tubes don’t shatter when you’re cycling the heat up and down quickly. The balancing act Now, here’s the catch. High-density IR arrays are incredibly powerful. If your belt speed is too slow, you’ll toast the surface of the glass before the inside is even warm. You have to find that sweet spot between wattage and dwell time to avoid those dreaded exterior “hot spots.” And one last thing: if you crank the power to clear out a stubborn dead zone, keep an eye on your cooling system. All that extra heat stays in the kiln housing, and if you don’t vent it, you’ll end up burning out your lamp sockets.