Glass melts at temperatures ranging from about 1,400°F (760°C) for simple fusing up to 2,900°F (1,600°C) for a full liquid state, depending on the type of glass and what you’re trying to do with it. Most hobbyists aren’t melting glass into a puddle. They’re softening it enough to fuse pieces together, shape it with a torch, or slump it into a mold. The method you choose depends on the scale of your project, your budget, and how much control you need over the result.
Types of Glass and Their Melting Points
Not all glass behaves the same way when heated. The two types you’ll encounter most often are soda-lime glass and borosilicate glass, and they require very different temperatures.
Soda-lime glass is the most common variety. It’s made from silica (sand) mixed with sodium carbonate and calcium oxide, which lower its melting point and make it easier to work with. It starts softening around 1,000°F (538°C) and reaches a full liquid state between roughly 1,400°C and 1,600°C (2,552°F to 2,912°F). Most fusing glass, stained glass, and bottle glass falls into this category.
Borosilicate glass contains boron oxide instead of lime, which makes it far more resistant to thermal shock. That’s why it’s used for labware and cookware. The tradeoff is a higher melting point, typically between 1,600°C and 1,700°C (2,912°F to 3,092°F). It requires hotter equipment and more skill to work with, though it’s popular among lampworkers who make pipes, beads, and sculptural pieces.
Why Glass Compatibility Matters
Every type of glass expands and contracts at a specific rate when heated and cooled, measured by its Coefficient of Expansion (COE). The two main COE ratings for fusible art glass are 90 and 96. If you combine glass pieces with different COE values in the same project, they’ll expand and contract at different rates as the piece cools. The result is internal stress that leads to cracking, sometimes hours or days after the piece comes out of the kiln.
The rule is simple: only fuse glass with the same COE. Don’t mix manufacturers unless you’ve confirmed compatibility. And never assume that two pieces of glass are compatible just because they look similar or came from the same store.
Three Ways to Melt Glass
Kiln Fusing
A kiln is the most versatile and controlled way to melt glass. Electric kilns with programmable controllers let you set exact temperatures and cooling rates, which is critical for consistent results. For beginners, a small kiln that plugs into a standard household outlet is a practical starting point. These are large enough to fuse jewelry, small dishes, tiles, and test pieces without requiring a dedicated electrical circuit.
In a typical fusing project, you stack cut glass pieces on a kiln shelf lined with kiln paper (a thin refractory sheet that prevents glass from bonding to the shelf). The kiln ramps up to your target temperature, holds there briefly, then follows a controlled cooling schedule. A full fuse, where separate pieces melt together into a single smooth layer, generally happens around 1,450°F to 1,500°F (788°C to 816°C). A tack fuse, where pieces stick together but retain some of their original shape, uses a slightly lower temperature.
Torch Work (Lampworking)
Lampworking uses a bench-mounted torch to melt glass rods, which you shape by hand using tools and gravity. This is the technique behind glass beads, marbles, pendants, and small sculptures. Most torches burn propane mixed with oxygen, delivered either from a compressed tank or an oxygen concentrator. A concentrator rated at 10 liters per minute or higher gives you enough oxygen flow for sustained work on medium-sized pieces. Smaller concentrators around 5 LPM will function, but they limit you to small work and slower melting.
You don’t need a kiln to melt the glass itself in lampworking, but you do need one to cool your finished pieces properly. A small annealing kiln holds completed work at a controlled temperature and brings it down slowly, preventing cracks from thermal stress.
Microwave Kilns
A microwave kiln is a small, insulated container lined with a special coating that absorbs microwave energy and converts it to heat. You place it inside a standard household microwave, and it reaches temperatures high enough to fuse small pieces of glass. A typical small project takes five to ten minutes to fuse. After heating, you leave the kiln closed and let it cool for about 30 minutes to avoid thermal shock.
This method is inexpensive and surprisingly effective for small items like cabochons, earring components, and simple pendants. It won’t replace a full kiln for larger or more precise work, but it’s a legitimate entry point for someone who wants to experiment without a major investment.
Cooling Glass Without Cracking It
The most common mistake beginners make isn’t in the heating. It’s in the cooling. Glass that cools too quickly develops internal stress that causes it to crack, sometimes explosively. The process of cooling glass in a controlled way is called annealing, and it’s not optional for any piece thicker than a few millimeters.
Annealing works by holding the glass at a specific temperature long enough for internal stresses to relax, then lowering the temperature in stages. For a common fusing glass like Bullseye (COE 90), the critical annealing temperature is around 900°F (482°C). A thin piece, about a quarter inch thick, needs roughly one hour at that temperature and can complete its full cooling cycle in about three hours. A one-inch slab needs a four-hour hold and around 14 hours total. A four-inch piece requires a 16-hour hold and roughly 170 hours, or about a full week, of controlled cooling.
Those numbers illustrate why thickness matters so much. If you’re making a simple fused pendant, cooling is quick and forgiving. If you’re casting a thick slab, it becomes the most time-consuming part of the entire process. Programmable kiln controllers handle this automatically once you enter the right schedule, which is why they’re worth the investment even for a first kiln.
Preventing Devitrification
Devitrification is a cloudy, whitish haze that forms on the surface of glass during firing. Glass artists call it “devit,” and it’s one of the most frustrating problems in kiln work. It happens when glass spends too long at certain temperatures, roughly between 1,300°C and 1,550°C (2,372°F to 2,822°F), giving crystalline structures time to grow within the glass. The result is a rough, scummy surface that ruins the clarity of your piece.
Several factors increase the risk. Dirty glass is a major one: fingerprints, dust, and surface contaminants act as seeds for crystal growth, so cleaning your glass thoroughly before every firing makes a real difference. Opaque glass, opal glass, and certain colored glass are also more prone to devitrification because the additives that create those effects already contain tiny crystalline areas where further crystal growth can take hold. Cooling too slowly through the devitrification zone also increases risk, which creates a tension with annealing. You want to cool slowly enough to anneal properly but not so slowly that crystals form. Using the right firing schedule for your specific glass resolves this.
Safety Essentials
Working with molten glass involves extreme heat, sharp edges, and potentially harmful fumes. Safety glasses are non-negotiable for any glass work, whether you’re cutting, fusing, or lampworking. For torch work specifically, you need didymium or shade-rated glasses that filter the bright sodium flare given off by hot glass. Regular sunglasses won’t protect your eyes from this type of light.
Ventilation is the other critical requirement. Kilns and torches release fumes from the glass itself, from coatings, and from any contaminants on the surface. Work in a space with adequate airflow that moves fumes away from your breathing zone, whether that’s a vented kiln hood, an exhaust fan, or an open workshop with good cross-ventilation. Enclosed, unventilated rooms are not safe for any type of glass melting.
Heat-resistant gloves, long sleeves, and closed-toe shoes round out the basics. Kilns and freshly fired glass retain heat far longer than most people expect. A kiln that looks cool from the outside can still be several hundred degrees inside.