Technical Glass
Glass is the transparent engineering material — and increasingly a precision one. Fused silica transmits from deep UV to infrared, expands one-twentieth as much as steel and shrugs off thermal shock; borosilicate is the laboratory and optical standard, cheap and chemically inert; ZERODUR glass-ceramic is what telescope mirrors and lithography stages are made from because it does not change size at all; chemically strengthened aluminosilicate survives the drops that break every phone-sized soda-lime pane; sapphire is technically a crystal but is bought and machined like a glass and is second only to diamond in hardness. All of it is brittle, all of it is shaped by grinding and polishing rather than cutting, and the strength you can use depends on the finish of the edges.
Glass by composition
BorosilicateSiO₂ + 13 % B₂O₃ · Borofloat 33, Pyrex, Duran, N-BK7460 – 64Laboratory glassware, sight glasses, viewports, cover slips, lamp envelopes, optical windows and lenses (N-BK7 is the default optical glass) — low expansion, inert, affordable, transmits 350 nm–2.5 µm.
Fused silica / fused quartz≥ 99.99 % SiO₂9—UV optics and lithography, semiconductor process tubes and boats, laser windows, high-temperature viewports, metrology — the lowest expansion of any glass, transmits 180 nm–3.5 µm, usable to 1,100 °C, immune to thermal shock.
Soda-limeSiO₂ + Na₂O, CaO · float glass, tempered, low-iron2—Windows, mirrors, display and touch-panel cover glass, shelves, cover plates, containers — the cheapest glass, available in large flat sheets and tempered for 4× the strength; greenish unless low-iron.
Aluminosilicate & chemically strengthenedSiO₂ + Al₂O₃, Na₂O · Gorilla Glass, Dragontrail4—Phone and device covers, instrument and automotive displays, thin protective windows — ion-exchange strengthened to survive drops and scratches at 0.4–1 mm thick; also high-temperature lamp and halogen envelopes.
Glass-ceramicsCrystallized Li-Al-Si glass · ZERODUR, Robax, Ceran, Macor660 – 90Telescope mirror blanks, lithography stages and metrology frames (ZERODUR — near-zero expansion); fireplace and cooktop panels and furnace windows (Robax, to 700 °C); machinable insulating fixtures (Macor).
Sapphire & optical crystalsSingle-crystal Al₂O₃ · CaF₂, ZnSe, Ge, Si35—Scratch-proof watch and sensor windows, high-pressure and high-temperature viewports, wafers, bearing jewels and nozzles (sapphire — 9 Mohs, usable to 1,800 °C, transmits UV to mid-IR); fluorides and semiconductors for IR and laser optics.
Choose a glass for
Windows, viewports, sight glasses, lenses and light guides — anywhere something must be seen through or transmitted through; laboratory, pharmaceutical and chemical-process components in contact with acids and solvents; substrates and wafers for optics, displays, sensors and microfluidics; high-temperature viewing and cooktop panels (glass-ceramic); precision metrology, mirror blanks and stages that must not move with temperature (ZERODUR, fused silica); and scratch-proof covers and bearing surfaces (sapphire).
Look elsewhere when
The part sees impact, point loads or tensile stress in service (polycarbonate or PMMA for guards and covers, a metal for anything structural), the geometry is a complex 3D solid rather than a plate, disc, tube or simple ground shape (glass is expensive to machine in three dimensions — consider a molded or printed transparent polymer), the part needs threads, snap-fits or tight fastener holes, or operating temperature exceeds the glass's limit (soda-lime softens around 500 °C; even fused silica sags at 1,100 °C). Hydrofluoric acid and hot alkalis attack every silicate glass.
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Glass by application
- Lenses, windows and optics
- N-BK7 for visible optics at the lowest cost; fused silica for UV, high-power laser and thermal stability; sapphire where the window must also be scratch-proof or hot.
- Heat and thermal shock
- Fused silica to 1,100 °C and any thermal shock; Robax glass-ceramic for panels seeing 700 °C flame; borosilicate for lab and process temperatures to ~450 °C.
- Chemical resistance
- Borofloat 33 and Duran for reactors, sight glasses and lab hardware; fused silica for ultra-pure and semiconductor chemistry. Neither resists HF or hot caustic.
- Dimensional stability
- ZERODUR (CTE ≈ 0 ± 0.02 ppm/K) for mirror blanks, stages and reference frames; fused silica (0.5 ppm/K) for the same at lower cost when a slight expansion is acceptable.
- Scratch and impact resistance
- Sapphire when nothing may scratch it (watch crystals, barcode scanner windows, sensor covers); chemically strengthened aluminosilicate for thin drop-resistant covers; tempered soda-lime for large panels and shelves.
AI suggestions — verify with an engineer before ordering. Estimates are indicative; the quote page prices your exact geometry.
Manufacturing notes
- CNC grinding and machining
- Glass is shaped with diamond tooling — CNC grinding, core drilling, edge profiling and ultrasonic machining — under flood coolant. Flats, discs, rings, holes, slots and pockets are routine to ±0.05 mm; polished optical surfaces to λ/10. Sapphire and glass-ceramics take the same processes more slowly. Every edge is seamed or polished, because a chipped edge is where a glass part starts to crack.
- Cutting sheet
- Score-and-break for straight cuts in float and borosilicate sheet, waterjet for profiles and thick plate, laser for thin display glass. Tempered glass cannot be cut or drilled after tempering — all machining is done first, then the part is heat- or chemically strengthened.
- Strengthening and forming
- Thermal tempering multiplies soda-lime strength by 4–5 and makes it break into safe fragments; chemical (ion-exchange) strengthening does the same for thin aluminosilicate and borosilicate. Slumping, bending and press-forming shape sheet at 600–800 °C; tubing is lathe-worked. Annealing after any hot process removes stress that would otherwise crack the part later.
- Joining and sealing
- Glass-to-metal seals use expansion-matched alloys (Kovar to borosilicate, Invar or titanium to specific glasses) or compression seals; glass bonds to glass by fusion, optical contact, frit or UV adhesive; anodic bonding joins glass to silicon for microfluidics. Structural glass assemblies are clamped with compliant gaskets, never bolted rigidly.
- Coatings and finishing
- Anti-reflection, mirror, ITO conductive, hydrophobic and hard coatings by vacuum deposition; screen printing and laser marking; frosting by sandblast or acid etch; edge and surface polishing grades from ground to optical. Coatings on the edges are as important as the face — the edge finish sets the usable strength.
Most-quoted glass grades
| Grade | Composition | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Weldability | Best for |
|---|---|---|---|---|---|---|---|
| Borofloat 33 | Borosilicate | 64 | 35 | 2.23 | Not recommended | Not recommended | Lab, process and viewport glass |
| N-BK7 | Borosilicate | 60 | 50 | 2.51 | Poor | Not recommended | Visible-range lenses and windows |
| Fused Silica | Fused silica / fused quartz | 90 | 50 | 2.2 | Not recommended | Not recommended | UV optics, heat, thermal shock |
| Soda-Lime | Soda-lime | 40 | 40 | 2.5 | Not recommended | Not recommended | Low-cost panels, covers, shelves |
| Gorilla Glass | Aluminosilicate & chemically strengthened | 700 | 350 | 2.42 | Not recommended | Not recommended | Thin drop-resistant display covers |
| ZERODUR | Glass-ceramics | 60 | 30 | 2.53 | Poor | Not recommended | Zero-expansion mirrors and stages |
| Sapphire | Sapphire & optical crystals | 400 | 400 | 3.98 | Not recommended | Not recommended | Scratch-proof, hot, high-pressure windows |
Finishes for glass
All 111 finishes8 of our 111 surface finishes take glass: 2 recommended outright, 4 with process care, 2 in limited cases. Each finish opens to its datasheet — thickness, hardness, salt-spray hours, spec codes and the glass-specific notes — and the configurator prices it on the grade you pick.
| Finish | Group | On glass | Thickness, µm | Hardness, HV | Salt spray, h | Cost |
|---|---|---|---|---|---|---|
| Anti-Fingerprint Oleophobic Coating | Paint, powder & polymer coatings | Yes | 0.01–2 | — | — | $$$ |
| Chemical Etching | Marking, decoration & colour | Yes | 5–100 | — | — | $$$ |
| Ink Stamping | Marking, decoration & colour | With care | 3–8 | — | — | $ |
| Laser Marking | Marking, decoration & colour | With care | 0–50 | — | — | $ |
4 more finishes accept glass — see the full material × finish matrix →
Glass — frequently asked
Borosilicate or fused silica?
Borosilicate (Borofloat 33, Pyrex, N-BK7) for most windows, lab and process parts and visible optics — it is a fifth of the price, easy to work and inert. Fused silica when the part must transmit UV below 350 nm, survive above 450 °C or sudden thermal shock, hold size within a micron, or handle high laser power. Both resist chemicals; only fused silica is truly pure SiO₂.
How strong is glass, really?
In compression, very — hundreds of MPa. In tension, only 30–70 MPa for ordinary annealed glass, and that number is set by surface and edge flaws, not the composition. Tempering or chemical strengthening raises the usable tensile strength to 150–700 MPa (Gorilla Glass at the top). Design glass parts to be loaded in compression, support them on compliant gaskets, and specify polished edges — a seamed edge can double the strength of the same pane.
Can glass be machined to tight tolerances?
Yes, by grinding. Dimensions to ±0.02 mm, flatness to a few microns and surface figure to a fraction of a wavelength are standard in optical shops; holes, slots, pockets and threads (in inserts) are routine in borosilicate and fused silica. The cost scales with the number of ground surfaces and the finish specified — ask for a polished surface only where light passes or strength requires it.
What is the difference between glass and glass-ceramic?
A glass-ceramic starts as a glass, is formed as a glass, and is then heat-treated to grow a controlled crystalline phase inside it. The crystals give properties glass cannot have: ZERODUR's near-zero thermal expansion, Robax's 700 °C service temperature, Macor's machinability. Most glass-ceramics are opaque or translucent; Robax and ZERODUR are among the few that stay clear.
Sapphire or Gorilla Glass for a display cover?
Gorilla Glass (chemically strengthened aluminosilicate) for anything larger than a watch face: it is thinner, lighter, far cheaper, and survives drops better because it is tougher and slightly flexible. Sapphire when scratch resistance is the whole requirement — watch crystals, scanner windows, camera covers — and the part is small enough that its brittleness and price are acceptable. Sapphire is harder than any sand or steel that could touch it; Gorilla Glass is not.