spore: profile
id: borosilicate-glass
spore_version: 0.2
family: glass-and-composites
name: Borosilicate glass
abbreviation: Borosilicate
role: optical and laboratory glass
category: glasses-optics
type: borosilicate
summary: |
  Borosilicate glass is a silica glass with about 13% boric oxide, which lowers its thermal expansion. SCHOTT's BOROFLOAT 33 sheet lists a density of 2.23 g/cm3, a transformation temperature of 525 °C and a long-term maximum operating temperature of 450 °C. Wikipedia reports that virtually all modern laboratory glassware is made of borosilicate, and that the 200 inch mirror of the Hale Telescope is borosilicate. The thermal expansion coefficient and thermal-shock ratings come from the SCHOTT technical-details page; see the property list for the values and conditions.
best_for: Laboratory glassware and optics that must survive temperature swings, where a low thermal expansion matters more than cost
weakest_at: Higher working temperature and processing cost than soda-lime glass; the expansion coefficient and hazard data could not be checked in this run
identity:
  formula: 'Silica-boria glass: about 80% SiO2, 13% B2O3, 4% Na2O or K2O and 2-3% Al2O3 for the low-expansion laboratory type'
  source: wikipedia-borosilicate
  where: Wikipedia, Borosilicate glass, Manufacturing process section (composition quoted as approximately 80% silica, 13% boric oxide, 4% sodium or potassium oxide and 2 to 3% aluminium oxide). Composition is a typical example, not a single specification; products such as BOROFLOAT 33 are defined by the manufacturer.
tags:
  environments: []
  stresses: []
  applications:
    - optics-and-cameras
    - electronics-and-chips
properties:
  - benchmark: density
    value: 2.23
    unit: g/cm3
    scope: material
    conditions:
      temperature: 25 °C
    method: Value printed in the mechanical properties table of the SCHOTT BOROFLOAT 33 technical details page
    status: ground
    source: schott-borofloat33
    where: Mechanical properties table, density row
  - benchmark: transformation_temperature
    value: 525
    unit: °C
    scope: material
    conditions:
      standard: ISO 7884
    method: Value printed in the thermal properties table of the SCHOTT page
    status: ground
    source: schott-borofloat33
    where: Thermal properties table, Tg row
  - benchmark: max_operating_temperature_short_term
    value: 500
    unit: °C
    scope: material
    conditions:
      duration: less than 10 h
    method: Value printed on the SCHOTT page, reference value
    status: ground
    source: schott-borofloat33
    where: Thermal properties table, maximum operating temperature row
  - benchmark: max_operating_temperature_long_term
    value: 450
    unit: °C
    scope: material
    conditions:
      duration: 10 h or more
    method: Value printed on the SCHOTT page, reference value
    status: ground
    source: schott-borofloat33
    where: Thermal properties table, maximum operating temperature row
  - benchmark: specific_heat
    value: 0.83
    unit: kJ/(kg·K)
    scope: material
    conditions:
      temperature_range: 20 to 100 °C
    method: Value printed in the thermal properties table
    status: ground
    source: schott-borofloat33
    where: Thermal properties table, specific heat row
  - benchmark: thermal_conductivity
    value: 1.2
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: 90 °C
    method: Value printed in the thermal properties table
    status: ground
    source: schott-borofloat33
    where: Thermal properties table, thermal conductivity row
  - benchmark: youngs_modulus
    value: 64
    unit: kN/mm2
    scope: material
    conditions:
      standard: DIN 13316
    method: Value printed in the mechanical properties table
    status: ground
    source: schott-borofloat33
    where: Mechanical properties table, Young's modulus row
  - benchmark: poissons_ratio
    value: 0.2
    unit: dimensionless
    scope: material
    conditions:
      standard: DIN 13316
    method: Value printed in the mechanical properties table
    status: ground
    source: schott-borofloat33
    where: Mechanical properties table, Poisson's ratio row
  - benchmark: knoop_hardness
    value: 480
    unit: HK0.1/20
    scope: material
    conditions:
      standard: DIN ISO 9385
    method: Value printed in the mechanical properties table
    status: ground
    source: schott-borofloat33
    where: Mechanical properties table, Knoop hardness row
  - benchmark: refractive_index
    value: 1.4714
    unit: nd (587.6 nm)
    scope: material
    conditions:
      wavelength: 587.6 nm
      note: reference value, not guaranteed by the manufacturer
    method: Value printed in the optical data table
    status: ground
    source: schott-borofloat33
    where: Optical data table, refractive index nd row
  - benchmark: abbe_number
    value: 65.41
    unit: dimensionless
    scope: material
    conditions:
      wavelength: nu_e
      note: reference value, not guaranteed by the manufacturer
    method: Value printed in the optical data table
    status: ground
    source: schott-borofloat33
    where: Optical data table, Abbe number row
  - benchmark: stress_optical_coefficient
    value: 4
    unit: x10^-6 mm2/N
    scope: material
    conditions:
      note: reference value, not guaranteed by the manufacturer
    method: Value printed in the optical data table
    status: ground
    source: schott-borofloat33
    where: Optical data table, stress-optical coefficient K row
  - benchmark: hydrolytic_class
    value: 1
    unit: class HGB (ISO 719 / DIN 12 111)
    scope: material
    conditions:
      standard: ISO 719 / DIN 12 111
    method: Class printed in the chemical durability table
    status: ground
    source: schott-borofloat33
    where: Chemical durability table, hydrolytic resistance rows
  - benchmark: cte
    label: Linear thermal expansion coefficient
    value: 3.25
    unit: x10^-6 K^-1
    scope: material
    conditions:
      temperature_range: 20 to 300 °C
      standard: ISO 7991
    method: Printed as 3.25 x 10-6 K-1 in the BOROFLOAT 33 brochure; same value on the 0407 data sheet and the Edmund Optics copy of the SCHOTT technical data sheet
    status: ground
    source: schott-media-datasheet
    where: 'Thermal properties table, Linear Thermal Expansion (C.T.E.) row, footnote *: according to ISO 7991'
  - benchmark: dielectric_constant
    label: Dielectric constant
    value: 4.6
    unit: dimensionless
    scope: material
    conditions:
      frequency: 1 MHz
      temperature: 25 °C
    method: Printed in the electrical properties list of the SCHOTT 0407 data sheet
    status: ground
    source: schott-datasheet-0407
    where: Electrical Properties, Dielectric Constant row
  - benchmark: dissipation_factor
    label: Loss tangent
    value: 37
    unit: x10^-4
    scope: material
    conditions:
      frequency: 1 MHz
      temperature: 25 °C
    method: Printed as 37 x 10-4 in the electrical properties list of the SCHOTT 0407 data sheet
    status: ground
    source: schott-datasheet-0407
    where: Electrical Properties, Loss Tangent row
  - benchmark: dielectric_strength
    label: Dielectric strength
    value: 16
    unit: kV/mm
    scope: material
    conditions:
      frequency: 50 Hz
      temperature: 25 °C
    method: Printed in the electrical properties list of the SCHOTT 0407 data sheet
    status: ground
    source: schott-datasheet-0407
    where: Electrical Properties, Dielectric Strength row
  - benchmark: flexural_strength
    label: Bending strength, normal conditions
    value: 25
    unit: MPa
    scope: material
    conditions:
      standard: DIN 52 292 Part 1
      basis: normal conditions
    method: Printed in the mechanical properties list of the SCHOTT 0407 data sheet
    status: ground
    source: schott-datasheet-0407
    where: Mechanical Properties, Bending Strength, For Normal Conditions
  - benchmark: flexural_strength
    label: Bending strength, safety conditions
    value: 7
    unit: MPa
    scope: material
    conditions:
      standard: DIN 52 292 Part 1
      basis: safety conditions
    method: Printed in the mechanical properties list of the SCHOTT 0407 data sheet; the lower design value for safety use
    status: ground
    source: schott-datasheet-0407
    where: Mechanical Properties, Bending Strength, For Safety Conditions
  - benchmark: annealing_point
    label: Annealing point (1013 dPa·s)
    value: 560
    unit: °C
    scope: material
    conditions:
      viscosity: 1013 dPa·s
    method: Printed in the thermal properties list of the SCHOTT 0407 data sheet
    status: ground
    source: schott-datasheet-0407
    where: Thermal Properties, Annealing Point row
  - benchmark: softening_point
    label: Softening point (10^7.6 dPa·s)
    value: 815
    unit: °C
    scope: material
    conditions:
      viscosity: 10^7.6 dPa·s
    method: Printed in the thermal properties list of the SCHOTT 0407 data sheet
    status: ground
    source: schott-datasheet-0407
    where: Thermal Properties, Softening Point row
corrosion:
  - environment: Water, 5 vol% hydrochloric acid and 0.02 n sulphuric acid (24 h at 95 °C)
    headline: Water and acids give negligible attack.
    effect: Abrasion below 0.01 mg/cm2 and surface unchanged in each test.
    conditions:
      time: 24 h
      temperature: 95 °C
    source: schott-borofloat33
    where: Chemical durability, Resistance to selected chemicals table
  - environment: 5% sodium hydroxide (6 h at 95 °C), 0.02 n sodium hydroxide, 0.02 n sodium carbonate
    headline: Alkali attacks the surface more than acid does.
    effect: '5% NaOH: abrasion 1.1 mg/cm2 with white stains. 0.02 n NaOH: 0.16 mg/cm2 with white haze. 0.02 n Na2CO3: 0.16 mg/cm2, unchanged.'
    conditions:
      time: 6 h
      temperature: 95 °C
    source: schott-borofloat33
    where: Chemical durability, Resistance to selected chemicals table
  - environment: 10% hydrofluoric acid (20 min at 23 °C) and 10% NH4F x HF
    headline: Hydrofluoric acid stains the glass; the buffered mix does not.
    effect: '10% HF: abrasion 1.1 mg/cm2 with stained white haze. 10% NH4F x HF: 0.14 mg/cm2, unchanged.'
    conditions:
      time: 20 min
      temperature: 23 °C
    source: schott-borofloat33
    where: Chemical durability, Resistance to selected chemicals table
  - environment: High-intensity UV from a mercury vapour lamp (365 nm main line, 15 h)
    headline: 'Low solarization: the glass darkens little under UV.'
    effect: SCHOTT describes low solarization and low auto-fluorescence. The before-and-after transmission curves are graphs; no single number is printed.
    conditions:
      source: HOK 4/120 lamp, 850 W/cm2, 30 x 15 x 1 mm sample
    source: schott-media-datasheet
    where: Solarization test figure and text
risks:
  hazards:
    - text: 'PubChem aggregated GHS for boron oxide (B2O3), the main oxide in the glass: H360 (95.1% of reports, Danger) May damage fertility or the unborn child; H360FD (13.1%) May damage fertility and the unborn child; H319 causes serious eye irritation; H335 may cause respiratory irritation; H303 may be harmful if swallowed. These describe the powder, not the solid glass.'
      ghs:
        - H360
        - H360FD
        - H319
        - H335
        - H303
      source: pubchem-boric-oxide
      where: Safety and Hazards, GHS Classification (CID 11073337)
  failure_risks:
    - mode: Thermal shock
      trigger: Temperature difference across the glass, short exposure (1 h)
      consequence: SCHOTT rates resistance to temperature differences at 110 K for a 1 h exposure, 90 K for 1 to 100 h and 80 K for over 100 h.
      severity: moderate
      source: schott-datasheet-0407
      where: Resistance to Temperature Differences (RTD1) list
    - mode: Thermal shock by panel thickness
      trigger: Temperature difference for a thermal shock resistance (RTS) rating, by thickness
      consequence: RTS is 175 K for under 4 mm, 160 K for 4 to 6 mm, 150 K for 6 to 15 mm and 140 K for over 15 mm.
      severity: moderate
      source: schott-datasheet-0407
      where: Resistance to Thermal Shock (RTS) list
    - mode: Impact
      trigger: Physical impact on an installed panel
      consequence: SCHOTT says impact resistance depends on how the glass is fitted, its size and thickness, and the type of impact.
      severity: moderate
      source: schott-tech-data-edmund
      where: Physical Impact paragraph
    - mode: Thermal shock (kitchenware comparison)
      trigger: Boiling vessel placed on ice
      consequence: Wikipedia says borosilicate withstands a change of about 330 °F without fracturing, against about 100 °F for soda-lime glass, and that borosilicate can still crack under rapid or uneven temperature change.
      severity: moderate
      source: wikipedia-borosilicate
      where: Thermal shock section
  side_effects: []
  handling:
    - text: Keep long-term use at or below 450 °C (short exposures of less than 10 h up to 500 °C), and keep temperature differences within the RTD and RTS limits in failure_risks.
      source: schott-borofloat33
      where: Maximum operating temperature; RTD1 list
    - text: Do not heat borosilicate glass with sodium hydride. The reaction can form sodium borohydride.
      source: wikipedia-borosilicate
      where: Laboratory section
  mitigations: []
uses:
  - application: optics-and-cameras
    device: Reflecting telescope primary mirror
    example: The 200 inch mirror of the Hale Telescope is made of borosilicate glass.
    source: wikipedia-borosilicate
    where: Optics section
  - application: optics-and-cameras
    device: Hot and cold mirrors and dichroic filters
    example: SCHOTT says BOROFLOAT 33 is the material of choice for high-temperature-resistant dichroic filters and hot and cold mirrors, because its high boron content gives a low thermal expansion.
    source: schott-media-datasheet
    where: BOROFLOAT 33 & Functional Coatings, mirrors section
  - application: optics-and-cameras
    device: Telescope mirror substrates
    example: SCHOTT lists telescope mirror substrates and glass-ceramics among its aviation, astro and space applications.
    source: schott-borofloat33
    where: Aviation, Astro and Space navigation list
  - application: optics-and-cameras
    device: Satellite mirror substrates
    example: SCHOTT lists satellite mirror substrates and electronic packaging in its aviation, astro and space applications.
    source: schott-borofloat33
    where: Aviation, Astro and Space navigation list
  - application: electronics-and-chips
    device: Electronic packaging
    example: SCHOTT lists electronic packaging alongside satellite mirror substrates in its space applications.
    source: schott-borofloat33
    where: Aviation, Astro and Space navigation list
  - application: solar-arrays
    device: Front-surface cover glass on silicon solar cells
    example: The NASA 1980 solar power satellite study says cerium-doped borosilicate meets the front-cover requirements if it can be bonded to the cell without thermal-mismatch damage; Corning 7070 borosilicate was used as a 250 um integral cover that survived annealing.
    source: nasa-sps-1980
    where: Cover glass section, text on front-surface cover requirements
supply:
  - subject: Boron (borates)
    abundance: 'USGS: borates are mostly in volcanic and arid-climate deposits; world reserves of refined borates are adequate for the foreseeable future. Boron is also on the USGS 2025 critical minerals list.'
    producers:
      - country: Turkey
        production: refined borates 1,500 thousand t (2025)
        reserves: 950,000 thousand t
        year: 2025
      - country: Bolivia
        production: ulexite 380 thousand t (2025)
        year: 2025
      - country: Chile
        production: ulexite 300 thousand t (2025)
        reserves: 35,000 thousand t
        year: 2025
      - country: Peru
        production: crude borates 220 thousand t (2025)
        reserves: 4,000 thousand t
        year: 2025
      - country: China
        production: boric oxide equivalent 230 thousand t (2025)
        reserves: 9,100 thousand t
        year: 2025
      - country: Argentina
        production: crude ore 170 thousand t (2025)
        year: 2025
      - country: Russia
        production: datolite ore 80 thousand t (2025)
        reserves: 40,000 thousand t
        year: 2025
      - country: Germany
        production: compounds 40 thousand t (2025)
        year: 2025
    critical_lists:
      - list: USGS 2025 Final List of Critical Minerals (published 7 Nov 2025)
        listed: true
    recycling: Not sourced.
    substitutes: []
    source: usgs-boron
    where: Salient statistics and World Production and Reserves table; critical minerals paragraph; the USGS table gives no country shares, so none are shown
  - subject: Boron import dependence (United States)
    abundance: 'USGS: import sources for all forms of boron, 2021 to 2024, as printed.'
    producers:
      - country: Turkey
        share_percent: 90
        year: 2021
        basis: 'year as printed: 2021-2024 imports'
      - country: Bolivia
        share_percent: 6
        year: 2021
        basis: 'year as printed: 2021-2024 imports'
      - country: Other
        share_percent: 4
        year: 2021
        basis: 'year as printed: 2021-2024 imports'
    critical_lists: []
    recycling: Not sourced.
    substitutes: []
    source: usgs-boron
    where: 'Import Sources (2021-24): All forms'
documents:
  - title: BOROFLOAT 33 technical details (SCHOTT)
    type: datasheet
    url: https://www.schott.com/en-us/products/borofloat/technical-details
  - title: Borosilicate glass (Wikipedia)
    type: report
    url: https://en.wikipedia.org/wiki/Borosilicate_glass
  - title: BOROFLOAT 33 & Functional Coatings (SCHOTT)
    type: datasheet
    url: https://media.schott.com/api/public/content/32b935120d7343109caa36fb70f40ced?v=541db792&download=true
  - title: SCHOTT BOROFLOAT data sheet 0407
    type: datasheet
    url: https://iosoptics.com/pdf/Schott-Datasheet-Borofloat-33.pdf
  - title: 'Mineral Commodity Summaries 2026: Boron (USGS)'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-boron.pdf
  - title: Boron oxide (B2O3), PubChem CID 11073337
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/11073337
  - title: Corning 7740 (Pyrex) property table, copy hosted by Valley Design
    type: datasheet
    url: https://valleydesign.com/wp-content/uploads/2023/11/corning-pyrex-7740.pdf
    year: 2023
  - title: NASA Solar Power Satellite System Definition Study (NTRS 19800004887)
    type: report
    url: https://ntrs.nasa.gov/api/citations/19800004887/downloads/19800004887.pdf
    year: 1980
gaps:
  - 'Silica sand and soda ash supply: no USGS MCS text read in this run; only the boron chapter was read.'
  - 'Corning PYREX 7740: corning.com returns HTML, not a PDF, in this run. A Valley Design copy of the Corning 7740 property table is cited instead (source valley-7740); its values are not yet used in properties.'
  - No safety data sheet for the finished glass was read. The hazard entry uses PubChem's classes for boron oxide, not for the glass.
  - No open peer-reviewed paper on borosilicate properties was found; no flight, vacuum or radiation test was found.
  - 'Source disagreement: the 0407 SCHOTT data sheet gives a transformation temperature of 530 °C and a Young''s modulus of 63 kN/mm2. The current SCHOTT technical page gives 525 °C and 64 kN/mm2. Both are kept with their own sources.'
  - 'Lab glassware: Wikipedia states it as virtually all modern lab glassware, but the application is not on the approved list, so it stays in story only.'
  - Wikipedia gives a CTE of 3.3 x10^-6 K^-1 at 20 °C for a generic lab borosilicate. That is not used as the BOROFLOAT value; it is recorded here only.
sources:
  schott-borofloat33:
    title: BOROFLOAT 33 technical details
    id: SCHOTT AG product page
    url: https://www.schott.com/en-us/products/borofloat/technical-details
    kind: datasheet
    license: manufacturer web page, cited not reproduced
  wikipedia-borosilicate:
    title: Borosilicate glass
    id: Wikipedia, Borosilicate glass
    url: https://en.wikipedia.org/wiki/Borosilicate_glass
    kind: web
    license: CC BY-SA 4.0
  schott-media-datasheet:
    title: BOROFLOAT 33 & Functional Coatings (SCHOTT brochure)
    id: SCHOTT AG, BOROFLOAT 33 & Functional Coatings
    url: https://media.schott.com/api/public/content/32b935120d7343109caa36fb70f40ced?v=541db792&download=true
    kind: datasheet
    license: manufacturer document, cited not reproduced
  schott-datasheet-0407:
    title: SCHOTT BOROFLOAT data sheet 0407 (SCHOTT North America)
    id: SCHOTT North America, data sheet 0407 (copy on IOS Optics site)
    url: https://iosoptics.com/pdf/Schott-Datasheet-Borofloat-33.pdf
    kind: datasheet
    license: manufacturer document, cited not reproduced
  schott-tech-data-edmund:
    title: BOROFLOAT 33 Technical Data (SCHOTT, copy on Edmund Optics)
    id: SCHOTT AG technical data sheet, Edmund Optics copy
    url: https://www.edmundoptics.com/ViewDocument/schott-borofloat-technical-data-sheet-english.pdf
    kind: datasheet
    license: manufacturer document, cited not reproduced
  usgs-boron:
    title: 'Mineral Commodity Summaries 2026: Boron'
    id: USGS, MCS 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-boron.pdf
    kind: report
    license: US government work, public domain
  pubchem-boric-oxide:
    title: Boron oxide (B2O3), PubChem CID 11073337
    id: PubChem, GHS classification of boric oxide
    url: https://pubchem.ncbi.nlm.nih.gov/compound/11073337
    kind: database
    license: PubChem, public domain
  valley-7740:
    title: 'Glass Silicon Constraint Substrates: Corning 7740 (Pyrex) and 7070 property table'
    id: Valley Design copy of the Corning 7740 and 7070 property table
    url: https://valleydesign.com/wp-content/uploads/2023/11/corning-pyrex-7740.pdf
    year: 2023
    kind: datasheet
    license: copy of a Corning property table, cited not reproduced
  nasa-sps-1980:
    title: Solar Power Satellite System Definition Study (NASA contract NAS9-15636)
    id: NASA NTRS 19800004887
    url: https://ntrs.nasa.gov/api/citations/19800004887/downloads/19800004887.pdf
    year: 1980
    kind: report
    license: NASA technical report, public distribution
license: CC-BY-4.0
updated: '2026-10-19'
review:
  status: draft
  method: assistant
  checked_values: 21
  unreachable: 4
  caveats: 2
  note: 'Written by an AI assistant on 2026-10-19. Deepen pass: added CTE, electrical and bending values, annealing and softening points (SCHOTT data sheets), corrosion from the SCHOTT chemical durability table, hazard classes (PubChem), supply (USGS MCS 2026), uses, failure and handling sections.'
story:
  recipe:
    line: Borosilicate glass is an amorphous silica network with boric oxide added. It is made by melting boric oxide, silica sand, soda ash and alumina together (Wikipedia). BOROFLOAT 33 is made by the float process, which SCHOTT describes as the world's first floated borosilicate glass. The composition below is the typical low-expansion laboratory type; the BOROFLOAT 33 recipe is not published as numbers.
    parts:
      - name: Silica
        symbol: SiO2
        share: about 80% (approximately; Wikipedia gives 'approximately 80%')
        role: The main network former. It gives the glass its rigid, mostly silica framework.
        share_percent: 80
      - name: Boric oxide
        symbol: B2O3
        share: about 13%
        role: Lowers the thermal expansion and the working temperature of the glass.
        share_percent: 13
      - name: Alkali oxide
        symbol: Na2O or K2O
        share: about 4%
        role: Helps the glass melt and adjusts its viscosity.
        share_percent: 4
      - name: Alumina
        symbol: Al2O3
        share: 2 to 3% (Wikipedia gives the range; share_percent uses the low end)
        role: Improves chemical durability.
        share_percent: 2
    source: wikipedia-borosilicate
    where: Wikipedia, Borosilicate glass, composition paragraph and Manufacturing process section
  risk_groups:
    - title: For people
      level: 0
      verdict: 'Hazard data partly checked: boric oxide classes read from'
      lead: 'PubChem''s aggregated GHS classes for boron oxide, the main glass oxide, are read below. No SDS for the finished glass was opened in this run. Hazard data partly checked: boric oxide classes read from PubChem; no SDS for the glass read'
      points:
        - label: Sharp edges
          line: Broken glass is sharp. Handle broken pieces with gloves and dispose of them in a sharps container.
        - label: Boric oxide
          line: PubChem's aggregated classes for boron oxide include H360 (may damage fertility or the unborn child, Danger) and H319 (eye irritation). These are for the powder, not for the finished glass.
        - label: Sodium hydride
          line: Do not heat borosilicate glass in contact with sodium hydride; the reaction can form sodium borohydride.
  why: Borosilicate glass is a silica glass with boric oxide added. The boron lowers the thermal expansion, so the glass is less likely to crack when it is heated or cooled quickly. That property is why most modern laboratory glassware is made from it, and why the 200 inch mirror of the Hale Telescope was cast from it.
  uses:
    - where: Optics
      line: The 200 inch mirror of the Hale Telescope is made of borosilicate glass, according to Wikipedia. Low-expansion borosilicate is also used for reflecting telescope mirrors in general.
    - where: Laboratory glassware
      line: Wikipedia states that virtually all modern laboratory glassware is made of borosilicate glass. No application from the approved list matches this use, so it is recorded here only.
    - where: Space and aviation
      line: SCHOTT lists telescope and satellite mirror substrates, and aircraft components for illumination, navigation and displays, among its borosilicate applications.
    - where: Hot and cold mirrors
      line: SCHOTT says BOROFLOAT 33 is the material of choice for high-temperature dichroic filters and hot and cold mirrors.
  can_do:
    - label: Density
      benchmark: density
      value: 2.23 g/cm3
      line: SCHOTT lists a density of 2.23 g/cm3 at 25 °C for BOROFLOAT 33, which is lighter than most soda-lime glass.
    - label: Working temperature
      benchmark: max_operating_temperature_long_term
      value: 450 °C
      line: SCHOTT gives a maximum long-term operating temperature of 450 °C, and 500 °C for short exposures of less than 10 h.
    - label: Transformation point
      benchmark: transformation_temperature
      value: 525 °C
      line: The transformation temperature is 525 °C per ISO 7884, the point where the glass stops behaving like a fully elastic solid in cooling tests.
    - label: Optics
      benchmark: refractive_index
      value: '1.4714'
      line: The refractive index at 587.6 nm is 1.4714, with an Abbe number of 65.41, which means low dispersion for a visible-light lens.
    - label: Thermal expansion
      benchmark: cte
      value: 3.25 x10^-6 K^-1
      line: SCHOTT gives 3.25 x 10-6 K-1 for 20 to 300 °C (ISO 7991). SCHOTT says this is three times lower than soda-lime glass.
  compare: Borosilicate glass has a linear thermal expansion of 3.25 x10^-6 K^-1 (20 to 300 °C), which SCHOTT puts at about one third of soda-lime glass. That low expansion gives it the thermal-shock limits in the 0407 data sheet (RTS 140 to 175 K by thickness). Its density of 2.23 g/cm3 and long-term limit of 450 °C are the figures on the SCHOTT sheet.
  compare_rows:
    - scope: material
      label: Density
      benchmark: density
    - scope: material
      label: Long-term working temperature
      benchmark: max_operating_temperature_long_term
    - scope: material
      label: Transformation temperature
      benchmark: transformation_temperature
    - scope: material
      label: Linear thermal expansion
      benchmark: cte
  handling:
    - Keep long-term use at or below 450 °C, and short exposures at or below 500 °C (under 10 h). SCHOTT gives these as the maximum operating temperatures.
    - 'Keep temperature differences within the SCHOTT RTD limits: 110 K for 1 h, 90 K for 1 to 100 h, 80 K for over 100 h.'
    - Do not heat in contact with sodium hydride; sodium borohydride can form.
    - Broken glass is sharp; handle it with gloves.
  good_for:
    - Lab glassware and optical parts that must tolerate temperature changes. SCHOTT's 450 °C long-term limit is the reference.
    - Telescope mirrors and lenses, where low dispersion (Abbe number 65.41) and a known refractive index matter.
  watch_out:
    - The expansion coefficient (3.25 x10^-6 K^-1) is for BOROFLOAT 33. Other borosilicate grades, such as the 3.3 value on Wikipedia, can differ.
    - Working limits are the manufacturer's reference values for BOROFLOAT 33, not guaranteed values for other borosilicate grades.
    - Solarization and fluorescence are described as low by SCHOTT, but no numbers are printed on the text pages read.
  verdict: Borosilicate is a sound choice where a low-expansion, durable glass is needed. This profile now has the thermal expansion, electrical and bending values, the chemical durability tests and the boric oxide hazard classes from sourced pages. Supply of silica and soda ash, the glass SDS and space testing are still open.