Lampworking creates objects under constant thermal stress. You're building with a 1900°F flame, adding layer after layer of molten glass, and then — at some point — the piece has to cool to room temperature without cracking. Annealing is what makes that possible. And yet it remains one of the most misunderstood steps in the lampwork process.
Glass is an amorphous solid — its molecules aren't arranged in a crystal lattice like metal. When you heat and cool glass rapidly, the outer layers cool faster than the interior, creating internal stress. If that stress exceeds the glass's tensile strength, it cracks — sometimes immediately, sometimes hours or days after the piece looks fine.
Annealing works by holding the glass at a temperature just below its strain point — typically around 900°F–960°F for borosilicate, 930°F–960°F for soft glass — long enough for the internal temperature to equalize. At this temperature, the glass is solid but its molecules have enough mobility to relieve stress. You then cool slowly through the strain point range, allowing the glass to set without introducing new stress.
Many lampworkers start by annealing in a fiber blanket box or improvised kiln. This works marginally but has real limitations: uneven temperature, no precise control of the cool-down rate, and no ability to batch anneal pieces that need different hold times.
A purpose-built annealing cabinet solves all of this. The Hot Shot 18A Annealing Cabinet ($4,317) is designed specifically for lampwork annealing workflows. It's always warm and ready to receive a hot piece, maintains a precise annealing hold temperature, and runs a controlled cool-down automatically. Available in 120V and 240V configurations.
The most common lampwork annealing mistake is using a general pottery or fusing kiln set to an annealing temperature. The problem isn't the temperature — it's the workflow. A pottery kiln takes 20–45 minutes to come up to annealing temp. Lampwork pieces need to go into a hot kiln immediately off the mandrel, before they can cool and develop stress.
An annealing cabinet stays hot all session. You open the door, drop the piece in, close the door. No waiting, no thermal shock from loading into a cold chamber, no interruption to your work flow at the torch.
Borosilicate (Pyrex, boro) anneals at a higher temperature than soft glass (Moretti/Effetre, Bullseye). If you work with both — which is uncommon but not unheard of — you'll need to adjust your annealing hold temp or keep two separate annealing setups. Mixing glass types without matching COE (coefficient of expansion) also creates stress that no amount of annealing will fix.
For most lampworkers, a single annealing temp dialed in for your primary glass type is all you need. Soft glass artists typically run 950°F, boro artists typically run 1050°F.
The annealing hold temp gets most of the attention, but the cool-down rate through the strain point is equally important. For most soft glass, the critical range is 950°F down to 700°F — drop no faster than 50°F–80°F per hour through this range. Below 700°F you can cool faster. A programmed controller handles this automatically.
Thicker or more complex pieces need slower cool-down rates than thin beads. A borosilicate sculpture with thick sections may need 25°F per hour through the critical range. Program conservatively until you know your work.
Learn more about the Hot Shot 18A Annealing Cabinet or browse our full glass kiln lineup.
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