Fixing Those Pesky Cold Spots in Glass Annealing
Anyone who’s worked with borosilicate glass knows the headache of internal stress. You need that thermal soak to be perfect, or you’re just waiting for the piece to crack. But here’s the problem: kilns aren’t perfect. If you’re working with weird shapes—think narrow necks or deep, chunky bases—you end up with “dead zones.” These are those annoying cold spots where the standard heating just can’t reach. That’s where short-wave IR lamps come in. They basically act like a spotlight for heat. Hitting the right spots Standard kiln heat is like a warm blanket; it’s everywhere, but it’s general. It doesn’t care about the “shadows” created by a complex piece of glassware. IR lamps are different. They send energy in straight lines. This means we can actually aim the heat exactly where the glass is struggling to warm up. By tweaking the wattage and where you place the lamp, you can force heat into the bottom of a flask or a tight corner without accidentally baking the rest of the chamber. Why quartz matters We use high-purity quartz for the lamp envelopes. Why? Because quartz lets that short-wave IR pass right through without soaking it up. You want the energy hitting the glass, not heating up the lamp housing. It also makes the system incredibly snappy. The moment your sensors pick up a temperature dip, the lamps kick in almost instantly. No waiting around for the air to warm up. A few things to watch out for Now, you can’t just plug these into a power strip and call it a day. You’ll need a dedicated control circuit and a stable voltage supply, otherwise, you’re just going to burn through bulbs. And a word of caution: these things are powerful. If you put a high-wattage lamp too close to a thin piece of glass, you’ll create a “hot spot.” That’s just as bad as a cold spot because it introduces new stresses or can even warp the glass. You have to find that sweet spot with the distance and the timing to keep the temperature climb gradual. Oh, and don’t forget some decent shielding. You don’t want that radiant heat frying your kiln’s internal wiring.