Getting the Heat Right for Silk-Screened Glass
Here’s the problem with silk-screening a wine glass: you’re dealing with two different materials that don’t always get along. You’ve got the glass—usually borosilicate or soda-lime—and then you’ve got that chemical ink layer. They react to heat in totally different ways. The real trick is the annealing stage. You need enough heat to bake the ink in and get rid of any internal stress in the glass, but you can’t go overboard. If you push the temperature too hard, you’ll either blur your beautiful pattern or, worse, end up with a pile of shattered glass. Why we go with Infrared We use shortwave IR lamps because they don’t mess around. They dive straight into the glass surface. Think about a convection oven—it heats the air, which then heats the glass. That’s too slow. IR lamps hit the material directly. But you have to be careful with the wattage and the distance. If the heat is too intense, the ink starts to bubble or bleed before the glass even gets warm. It’s all about finding that sweet spot where the glass stabilizes but the ink stays crisp and clean. The Hardware (and the headaches) Most of our setups run on quartz halogen tubes. I love them because they ramp up instantly. The glass hits the zone, the heat kicks in, and the second the glass leaves, the heat is gone. No over-baking. Simple. But they aren’t without their quirks. You have to keep an eye on your voltage. These tubes pull a lot of current. If your wiring is flimsy, you’ll get flickering or weird hot and cold spots across your conveyor. And man, these things are fragile. One accidental bump during install or a tiny splash of cooling fluid, and the tube is toast. Making the Workflow Actually Work To keep the glass from freaking out—what the engineers call “thermal shock”—we don’t just blast it with heat. We use zones. The first zone just gently pre-warms the glass. Then, the second zone hits the peak annealing temperature. It’s a gradual climb. If you try to do it all in one giant blast of heat, the stem of the wine glass will almost always snap. By staging the heat, the glass stays strong and your print looks sharp. It just works better.