N-BAK4
N-BAK4 is a barium crown glass from the lead-free N-series optical catalogue, selected for high internal transmittance over long glass paths.
Reference datasheet — N-BAK4 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the ANN condition
N-BAK4 tempers and conditions
N-BAK4 is supplied in 2 conditions, soft to hard. ANN is the default FabDigit quotes; the values on this page are for it.
Compare all 2 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ANNDefault Annealed | Choose fine annealed blocks or strips as the standard stock for conventional cold-working routes to prisms and lenses. | 50 | 0 | 590 HV | 0.85 W/m·K | |
High transmittance melt variant | Pick the melt made with low coloring impurities when 400–450 nm internal transmittance drives long optical paths, such as prism assemblies and sighting optics needing accurate color rendering. | 50 | 0 | 590 HV | 0.85 W/m·K |
Supply forms, finishes and certifications
Ways N-BAK4 is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
PRESS | Pressed blanks / near-net preforms | Surface finish |
What is N-BAK4?
N-BAK4 is a barium crown glass from the lead-free N-series optical catalogue, selected for high internal transmittance over long glass paths. It is used almost exclusively for roof and porro prisms in binoculars and rifle scopes, and is supplied annealed, heat-treated or as pressed near-net blanks (ANN, HT, PRESS). It is brittle and workable only with diamond tooling (machinability rating 28), is not weldable, and must be annealed after any hot step to remove stress birefringence. N-BK7 is the lower-cost substitute where path length is short. N-BAK4 has a density of 3.1 g/cm³ (0.112 lb/in³), heavier than 55% of glass grades. N-BAK4 has a tensile strength of 50 MPa (7.25 ksi), stronger than 59% of glass grades. Elongation at break is 0% and the elastic modulus is 77 GPa (11.2 Msi).
What is N-BAK4 used for?
- Roof/porro prisms
- Binoculars
- Rifle scopes
Limitations
- Poor heat conductor — 0.85 W/m·K (0.491 BTU/hr·ft·°F), worse than 86% of glass grades
N-BAK4 properties
Typical room-temperature values for N-BAK4-ANN; bars are the position among glass grades.
Physical3
N-BAK4 has a density of 3.1 g/cm³ (0.112 lb/in³), heavier than 55% of glass grades.
Mechanical13
N-BAK4 has a tensile strength of 50 MPa (7.25 ksi), stronger than 59% of glass grades. Elongation at break is 0% and the elastic modulus is 77 GPa (11.2 Msi).
Thermal5
N-BAK4 is rated for continuous service to 400°C (752 °F). It conducts heat at 0.85 W/m·K (0.491 BTU/hr·ft·°F), worse than 86% of glass grades. Thermal expansion is 7 µm/m·K (3.89 µin/in·°F).
Electrical3
N-BAK4 has an electrical resistivity of 1×10¹³ Ω·m.
Chemical & Environmental2
Corrosion resistance is good (68/100), worse than 62% of glass grades.
Sustainability4
Producing a kilogram of N-BAK4 takes about 45 MJ of energy and emits 2.8 kg of CO₂ — less than 58% of glass grades. Typical recycled content is 10%.
Manufacturability2
N-BAK4's machinability is poor (28/100, better than 66% of glass grades).
Common Calculations4
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the glass family
Yield strength against density for every glass grade FabDigit runs. N-BAK4 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with N-BAK4
Is N-BAK4 easy to machine?
Cut, mill and grind with diamond tooling only; ultrasonic and laser machining are also used. Keep feeds light and coolant flow generous to avoid edge chipping and subsurface cracks.
Can N-BAK4 be welded?
Not weldable. Assemble into metal barrels with adhesive bonding or elastic retaining rings, and cement prisms with optical UV adhesive or Canada balsam.
Can N-BAK4 be formed, bent or molded?
Can be hot pressed into near-net blanks near the softening point. Precision annealing after forming is mandatory to remove stress birefringence.
N-BAK4 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| SiO2indicative content, manufacturer formula proprietary | 40 – 55 | 48 |
| B2O3indicative | 5 – 15 | 10 |
| BaOcharacteristic oxide of barium crown glass | 15 – 30 | 22 |
| ZnOindicative | 0 – 10 | 5 |
| Na2O + K2Oalkali flux | 3 – 12 | 7 |
| PbO / As2O3N series is a lead-free, arsenic-free formulation | 0 | 0 |
What surface finishes work on N-BAK4?
Conventional rough grinding, fine grinding and pitch polishing reach λ/10. Clean and dry immediately after polishing, then apply AR or total-reflection coatings; avoid humid storage, which causes fogging.
How much does N-BAK4 cost?
N-BAK4 is a high-cost glass ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
N-BAK4 — frequently asked
What is N-BAK4 used for?
N-BAK4 is typically used for roof/porro prisms, binoculars and rifle scopes. In short: prism-grade barium crown; high transmittance, long paths; binocular and scope standard.
What is the tensile strength of N-BAK4?
N-BAK4 has a typical tensile strength of 50 MPa (7.25 ksi) — stronger than 59% of glass grades. Strength varies by condition: see the 2 listed tempers.
Is N-BAK4 easy to machine?
Not especially — machinability is rated poor (28/100, better than 66% of glass grades). Cut, mill and grind with diamond tooling only; ultrasonic and laser machining are also used. Keep feeds light and coolant flow generous to avoid edge chipping and subsurface cracks.
Can N-BAK4 be welded?
Not weldable. Assemble into metal barrels with adhesive bonding or elastic retaining rings, and cement prisms with optical UV adhesive or Canada balsam.
What surface finishes work on N-BAK4?
Conventional rough grinding, fine grinding and pitch polishing reach λ/10. Clean and dry immediately after polishing, then apply AR or total-reflection coatings; avoid humid storage, which causes fogging.
Can N-BAK4 be formed, bent or molded?
Can be hot pressed into near-net blanks near the softening point. Precision annealing after forming is mandatory to remove stress birefringence.
What is the maximum service temperature of N-BAK4?
N-BAK4 is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does N-BAK4 cost?
N-BAK4 is a high-cost glass ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- SCHOTT Optical Glass Data Sheets (N-BAK4) — SCHOTT AG (2023)
- TIE-29/TIE-33 Technical Information: Refractive Index and Mechanical Properties of Optical Glass — SCHOTT AG (2016)
- RefractiveIndex.INFO — barium crown glass dispersion data — RefractiveIndex.INFO (2024)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.