One of the questions we hear surprisingly often is simple:
Is it really glass? And does it break?
The short answer to both is yes.
Borosilicate is real glass, and like any glass, it can break if dropped hard enough. But it is quite different from the ordinary soda-lime glass used for most bottles, jars and windows.
At 78 Glass, borosilicate is the material behind almost everything we make. We chose it not only because of its technical properties, but because of the way it looks, reacts to light and allows us to work with color.
A Glass Made for More Demanding Jobs
Borosilicate glass was developed in Germany in the late 19th century by glass chemist Otto Schott.
The goal was to create glass that could perform in environments where ordinary glass struggled — particularly around heat, temperature changes and chemicals.
In the early 20th century, similar low-expansion glasses were developed in the United States by Corning. This work eventually led to Pyrex and helped make borosilicate a standard material for laboratories, scientific equipment and technical applications.
More than a century later, the same basic family of glass is still used wherever stability, transparency and resistance to temperature changes matter.
What Makes Borosilicate Different?
The key is in its composition.
Like most glass, borosilicate is based primarily on silica. But its formula also contains boron oxide along with several other components that modify how the final glass behaves.
One of the most important results is a very low coefficient of thermal expansion, usually shortened to COE or CTE.
The borosilicate we work with is commonly referred to as 33 COE, or borosilicate 3.3.
In simple terms, this means that the glass expands and contracts much less when its temperature changes than ordinary soda-lime glass does.
That makes it much more resistant to thermal shock and allows it to handle the repeated heating and cooling involved in lampworking.
It is also chemically durable, non-porous and resistant to abrasion.
But none of this means it is unbreakable.
A hard impact against stone, concrete or tile can still break borosilicate. It is better to think of it as technical glass designed to tolerate demanding conditions, rather than some kind of transparent metal.
The Part We Really Like: Optics
The technical properties are useful.
The optical properties are what made us fall in love with the material.
High-quality clear borosilicate has excellent transparency and optical clarity. Light passes through it, reflects from its surfaces and refracts through curves, edges and internal structures.
On a simple transparent piece, this is already visible.
Once you start adding geometry, layers and color, things become much more interesting.
A shape that looks almost completely transparent from one angle can suddenly produce reflections, bright edges or distorted views from another. Thick sections behave differently from thin ones. Internal lines can appear to move as the piece rotates.
Color adds another layer to all of this.
That interaction between material, shape, color and light is one of the main reasons we keep working with borosilicate.
Sometimes the optical effect is planned.
Sometimes the glass surprises us.
How Does Colored Borosilicate Work?
Colored glass is not simply clear glass with ordinary pigment mixed into it.
Its color comes from carefully controlled glass chemistry. Different metallic oxides and other compounds can produce different colors and optical effects depending on their concentration, oxidation state and the composition of the glass around them.
Cobalt compounds, for example, have traditionally been used to produce blues. Other elements and combinations can create reds, greens, purples, ambers and a huge range of more unusual effects.
But there is another important part of the process.
The colored glass still needs to remain compatible with the clear borosilicate around it.
Its thermal expansion, viscosity and working characteristics have to stay within the correct range. If two glasses expand and contract too differently, internal stress can develop where they meet.
So developing a good borosilicate color is a balancing act between chemistry, color and physical compatibility.
This is one reason why different colors can behave surprisingly differently at the torch even when they all belong to the same 33 COE family.
Some are extremely stable and predictable.
Others are considerably more temperamental.
And sometimes the difficult ones are the most interesting.
The Glass We Use
For our colored work, we use high-quality borosilicate produced by specialist glass manufacturers, with much of our color palette coming from the United States.
Some colors have been industry standards for years. We know how they move, how they react to heat and what they will look like after annealing.
Others come from smaller manufacturers or experimental production runs.
Those are especially interesting to us.
We are constantly looking for unusual colors, new formulations and limited glass batches that can produce something we have not worked with before.
Sometimes a new glass becomes part of our regular palette.
Sometimes it becomes one small drop and never appears again.
That uncertainty is part of the process.
More Than Just Durable Glass
It would be easy to describe borosilicate simply as stronger, heat-resistant glass.
But that misses a large part of why we use it.
For us, it is a material that sits somewhere between engineering and art.
Its low thermal expansion makes it possible to shape complex pieces with a torch. Its chemical and physical stability makes the finished object practical. And its transparency, refraction and huge range of available colors give us an almost endless space to experiment visually.
So yes — it is glass.
And yes — you can break it.
But there is a lot more going on inside it than there first appears to be.