N-BAK4 HT
Heat-treated state
HT = 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.
Values for the HT condition
Other N-BAK4 tempers and conditions
N-BAK4 is listed in 2 conditions; see the grade overview at N-BAK4.
- ANN
- HT
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 |
HTThis page 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 |
What is N-BAK4 HT?
N-BAK4 HT is N-BAK4 heat treated to HT — 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. N-BAK4 HT 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). N-BAK4 HT has a density of 3.1 g/cm³ (0.112 lb/in³), heavier than 55% of glass grades. ANN is the default condition FabDigit quotes; HT is available on request or by drawing note.
Limitations
- Poor heat conductor — 0.85 W/m·K (0.491 BTU/hr·ft·°F), worse than 86% of glass grades
N-BAK4 HT properties
Typical room-temperature values for N-BAK4 HT; 16 are specific to this condition. Other listed values are N-BAK4 reference data and may not represent this condition. Bars are the position among glass grades.
Physical3
N-BAK4 HT has a density of 3.1 g/cm³ (0.112 lb/in³), heavier than 55% of glass grades.
Mechanical13
N-BAK4 HT 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 HT 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 HT 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 HT 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 HT's machinability is poor (28/100, better than 66% of glass grades).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with N-BAK4 HT
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.
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.
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 |
N-BAK4 HT — frequently asked
What is N-BAK4 HT used for?
N-BAK4 HT 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 HT?
N-BAK4 HT 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 HT 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 HT 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 HT?
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 HT 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 HT?
N-BAK4 HT 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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.