When collectors hold my finished glass artwork, they often marvel at the vibrant colors and delicate textures. However, behind every sculpture lies a strict foundation of material science, thermodynamics, and physics.
One of the most frequent questions I receive at my studio in Sherwood Park, Alberta, is why I use completely different types of raw glass for different projects. The answer comes down to a critical scientific property known as COE, or the Coefficient of Expansion.
Understanding COE is essential to explaining why the delicate botanical glass flowers I sculpt at the torch are made from a completely different family of glass than the pieces I use for my kiln-fired pâte de verre artwork.
What is COE and Why Does It Matter?
In materials science, the Coefficient of Expansion (COE) is a fractional measure of how much a specific material expands when heated and contracts when cooled.
Plaintext
[Heating] ➔ Glass Molecules Expand at Rate X
[Cooling] ➔ Glass Molecules Contract at Rate X
Every single formulation of glass has its own distinct COE rating. When creating fine art, glasses with different COE numbers cannot be fused or melted together.
The Danger of Incompatibility: Thermal Stress
If you force two incompatible types of glass together while hot, they may look perfectly fused when they first come out of the heat. However, because they shrink at different speeds as they cool down to room temperature, they will pull against one another. This mismatch creates massive internal thermal stress.
Eventually, that trapped energy will release, causing the artwork to spontaneously crack, shatter, or completely fracture down the center. To prevent this, professional glass studios must strictly segregate their inventories by COE.
Why I Use COE 104 Glass for Flame-Worked Flowers
The intricate, dimensional flowers, leaves, and wearable jewelry components I create are crafted using a hot-shop technique known as lampworking (or flameworking). This involves melting solid glass rods directly inside a high-temperature oxygen-propane torch flame.
For this specialized torch work, my absolute standard is COE 104 glass (often referred to as "soft glass" or soda-lime glass, manufactured by historic houses like Effetre or CIM). As a side note- I ABSOLUTELY LOVE CIM GLASS!!
Features of COE 104 and Why It Excels for Lampworking:
Long Working Window- It stays pliable and workable over a wide temperature range, allowing me to precisely sculpt realistic petals, fine stamens, and organic leaf veins before it hardens.
High Viscosity- Molten COE 104 holds its shape beautifully under the torch flame without liquefying too quickly, allowing for complex dimensional layering.
Vast Color Palette & Chemistry- The color range is unmatched, featuring specialized reactive glasses containing silver, copper, or sulfur. These elements chemically react to the torch flame's chemistry, creating stunning, variegated organic finishes that mimic real flowers.
Why I Use COE 96 Glass for Pâte de Verre and Kiln-Fusing
My pâte de verre (literally translated from French as "glass paste") collections require an entirely different manufacturing philosophy. Instead of being shaped live in a flame, finely crushed glass powders and granules called frit are packed into a custom refractory mold and slow-fired inside a computer-controlled digital kiln.
For all of my kiln-formed and fused glass art, I use a dedicated COE 96 glass system (such as Oceanside).
The Advantages of COE 96 in the Kiln:
- Total System Compatibility: COE 96 is engineered specifically for testing and consistency. It ensures that sheet glass, coarse frits, fine powders, and thin stringers (glass threads) will fuse together flawlessly without structural stress.
- Predictable Devitrification Resistance: It is formulated to resist devitrification—a cloudy, dull crystallization that can form on the surface of glass when it spends extended hours at high temperatures inside a kiln.
- Exquisite Translucency: In pâte de verre work, COE 96 powders allow for incredibly subtle color blending and a sugary, semi-translucent surface texture that catches the light like frozen water.
Can You Mix COE 96 and COE 104 Together?
The Professional Rule: No. They are fundamentally incompatible.
Because their rates of expansion and contraction are wildly different, mixing COE 96 and COE 104 is a recipe for structural failure. Think of it like building a house frame out of two materials that expand at drastically different rates in the summer heat—eventually, the joints will tear themselves apart.
To ensure the lifetime durability of my collections, I maintain a strict division in the studio:
- The Torch Station: Exclusively stocked with COE 104 rods.
- The Kiln & Mold Prep Area: Exclusively stocked with COE 96 frits and sheets.
Balancing Artistry and Material Science
The artistic beauty of glass often steals the spotlight, but the technical mastery of chemistry, pyrometry, and physics is what allows that beauty to endure. Neither glass type is superior; they are simply specialized tools optimized for different artistic goals.
The next time you view my botanical collections, you'll know that while they share a common thread of color, light, and craftsmanship, they belong to two completely separate chemical families—each chosen precisely to ensure your handmade artwork stands the test of time.
