Cut a piece of glass, and you’re left with a raw edge — sharp, brittle, and structurally weak. That edge is the first thing to chip, the first thing to crack under thermal stress, and the first thing a client’s hand will touch. Edge-working is how that raw cut becomes a finished, safe, load-bearing edge. It sounds simple. In practice, it’s one of the most misunderstood steps in glass fabrication, even among people who work with glass every day.
This piece walks through the technical side of edge-working — the edge types, the machines, the standards, and the failure points — in plain language. If you cut, edge, or spec glass for a living, some of this will be familiar. Some of it, especially around stress risers and edge-strength testing, might not be.
Why the Edge Matters More Than People Think
Glass doesn’t fail from the middle. It fails from the edge.
When glass is cut, the cutting wheel or laser creates microscopic fractures along the edge — invisible to the eye, but very real under a microscope. These are called stress risers or flaws, and they’re where cracks start. A pane of glass under thermal or mechanical stress will almost always fail at its weakest edge flaw first, not because the glass itself is weak, but because that flaw concentrates stress like a notch in a rope.
Edge-working exists to remove or minimize these flaws. A well-worked edge isn’t just about looking clean for the customer — it directly affects the glass’s mechanical strength, its resistance to thermal breakage, and in tempered glass, whether it will even survive the tempering oven without spontaneously fracturing.
That last point is worth sitting with. Poor edge quality is one of the leading causes of breakage during the tempering process itself, before the glass ever reaches a job site. If you’ve ever had a batch of lites come out of the furnace with edge cracks and no obvious cause, the edge prep — not the temper cycle — is usually the first place to look.
The Main Edge Types (And When to Use Each)
Edge names vary a bit by region and shop, but these are the standard profiles you’ll run into on nearly every job.
Seamed (Arris) Edge
This is the baseline. A seamed edge just knocks off the sharp corners left by cutting — enough to make the glass safe to handle, nothing more. It’s not polished, not decorative. You’ll see this on glass that’s going into a frame or channel where the edge won’t be visible or touched, like most standard IGUs (insulated glass units) before they go into a sealed unit.
Flat Polished Edge
A flat polished edge is ground flat and then polished to a clear, glossy finish — a 90-degree edge with no bevel. This is the standard for shower doors, tabletops, shelving, and any application where the edge is exposed and needs to look finished. It’s also frequently required as a base step before tempering, since tempering furnaces are unforgiving of rough or seamed edges.
Pencil Edge
Rounded on both faces into a smooth, bullnose-like profile — literally shaped like the rounded tip of a pencil. It’s popular for mirrors and glass shelving because there’s no sharp line to catch on anything, and it reads as soft and finished without the cost of a full bevel.
Beveled Edge
The edge is ground at an angle (commonly 1 inch wide at roughly 15–20 degrees, though this varies by spec) to create a faceted, decorative look that catches light along the perimeter. Beveling is common in mirrors, glass doors, and tabletops where the client wants a premium, dimensional appearance. It’s slower and more labor-intensive than a flat polish, and it’s usually priced accordingly.
OG (Ogee) Edge
A double-curve profile — concave then convex, like classic wood or stone molding profiles. You’ll mostly see this on high-end tabletops and countertops where the glass is meant to visually echo furniture-grade detailing.
Mitered Edge
Used where two pieces of glass meet at a corner, typically 45 degrees, so the joint reads as a clean, continuous line rather than a butt joint. Common in glass shower enclosures and display cases. Miter accuracy is unforgiving — even a half-degree of error becomes visible as a gap once the pieces are assembled.
Waterfall Edge
Increasingly common on glass countertops and high-end retail displays — the glass edge is polished to allow it to appear to flow continuously from a horizontal surface into a vertical one, usually by mitering two polished pieces together at the corner. It reads as a single unbroken surface even though it’s two separate lites.
How Edge-Working Actually Happens
Most fabricators run one of three basic approaches, often in combination:
Straight-line edging machines run the glass along a fixed axis past a series of grinding and polishing wheels — typically diamond wheels for the initial grind, followed by progressively finer cerium oxide or polishing wheels for the final shine. These machines are fast and consistent for straight edges on rectangular lites, which covers the large majority of architectural and commercial glass.
CNC edging (shape edgers) handle curves, notches, and custom profiles that a straight-line machine can’t. A CNC edger follows a programmed path, which makes it the tool of choice for custom shapes, radiused corners, and non-rectangular glass like elliptical tabletops or curved shower panels. The tradeoff is speed — CNC edging is significantly slower per piece than straight-line work, so shops reserve it for shapes that genuinely require it.
Hand-edging (belt sanders, hand tools) still has a place, mostly for touch-up work, small runs, repair jobs, or edges that a machine can’t reach — like an inside corner or a field-cut modification. It’s slower and more operator-dependent, but for a one-off repair it’s often the only practical option.
A typical edge-working sequence looks like this:
- Rough grind — removes the bulk of material and cutting flaws with a coarse diamond wheel.
- Fine grind — refines the shape and reduces the roughness left by the rough grind.
- Polish — brings the edge to its final clarity, typically with felt or cerium oxide wheels.
- Inspection — check under raking light or magnification for flares, chatter marks, or missed flaws.
Skipping steps to save time is the most common cause of edge defects that show up later—either as haze under certain lighting or as breakage points that reveal themselves only under load or heat.
Standards That Actually Matter
In the US, ASTM C1036 (Standard Specification for Flat Glass) primarily governs edge quality, defining edge condition categories—including seamed, ground, and polished edges—and setting tolerances for chips, checks, and other visible flaws. For tempered and heat-strengthened glass, ASTM C1048 references edge condition requirements as part of the overall spec, since edge quality directly affects whether tempered glass will pass without spontaneous breakage.
If you’re fabricating for tempering, the practical rule of thumb most shops use is: any edge flaw deeper than roughly 1/16 inch (about 1.5mm) is a real risk point in the furnace. That’s not an official number in every spec, but it’s a widely used shop-floor threshold, and it’s worth knowing even if it’s not something you’ll find printed on a certificate.
For safety glazing generally, edges also need to meet the requirements referenced under ANSI Z97.1 and, where applicable, building code requirements tied to CPSC 16 CFR 1201 for tempered safety glazing in hazardous locations. None of these standards dictate an aesthetic edge profile — that’s a design choice — but they do set the floor for what counts as structurally acceptable.
Common Edge Defects (and What Actually Causes Them)
A few defects come up often enough that they’re worth naming specifically:
- Flares — small feather-shaped chips that run into the edge, usually from a dull or damaged grinding wheel, or from feeding the glass too fast through the machine.
- Chatter marks — a rippled, washboard texture on the polished surface, typically from a worn wheel, vibration in the machine, or inconsistent feed speed.
- Subsurface damage — flaws that don’t reach the surface but sit just below it. These are the dangerous ones, because they’re invisible without magnification or specialized inspection, and they’re a common source of “unexplained” breakage well after installation.
- Orange peel texture — a dimpled, uneven polish usually caused by polishing too fast or with worn-out polishing pads before the fine-grind stage is fully complete.
Most of these trace back to the same root causes: worn wheels, incorrect feed speed, or skipping a grind stage to save cycle time. Preventive wheel maintenance and consistent feed rates solve the majority of edge quality complaints before they ever reach a customer.
A Quick Note for Anyone Newer to the Trade
If you’re newer to edge-working: the edge type a client asks for is often a style decision, but the edge quality underneath it is not optional, regardless of which profile is chosen. A beautifully beveled edge with an unaddressed subsurface flaw is still a structural liability — it just hides it better. Always inspect under raking light before polish, not just after.
Choosing the Right Edge for the Job
| Application | Common Edge Choice | Why |
|---|---|---|
| Insulated glass units (concealed edge) | Seamed | Not visible once sealed; cost-efficient |
| Shower doors, tabletops | Flat polish or pencil | Exposed edge, needs to be safe to touch |
| Mirrors | Pencil or bevel | Soft, finished look at reasonable cost |
| Premium countertops, retail displays | OG, bevel, or waterfall | Decorative, higher-end appearance |
| Shower enclosure corners | Mitered | Clean visual joint between panels |
| Glass going into tempering | Flat polish or seamed (per furnace spec) | Reduces flaw-driven breakage risk in the oven |
The Bottom Line
Edge-working sits at the intersection of aesthetics and structural integrity, and it’s easy to treat it as purely cosmetic — pick a profile, run it through the machine, move on. But the edge is where glass is weakest, where breakage starts, and where a rushed process shows up later as a customer complaint or a warranty claim. Getting the edge right isn’t the flashy part of glass fabrication. It’s the part that keeps everything else from cracking.
