spore: profile
id: black-chrome
spore_version: 0.2
family: coatings
name: Black chrome (solar selective plating)
role: solar-selective absorber coating
category: coatings
type: optical-coatings
summary: |
  Black chrome is an electroplated, chromium-containing black layer that absorbs sunlight and radiates little infrared heat, so it is used as a solar selective coating. NASA Lewis Research Center discovered the solar selective property. On commercial electroplated tin on steel, black chrome plated for about 2 minutes gave an absorptance of 0.97 and an emittance of 0.06 (NASA TM-73799). A NASA survey table lists black chrome at 0.9 absorptance and 0.1 emittance. Above 300 degC, in air or vacuum, black chrome loses absorptance irreversibly, to 0.85 or less (NASA TM-81385).
best_for: Solar-thermal absorber surfaces up to about 300 degC, where high sunlight absorptance (0.9 in NASA Table 1) and low infrared emittance (0.1) are wanted at low cost
weakest_at: Heat above 300 degC, where absorptance falls irreversibly (NASA TM-81385), and steel without a nickel underlayer, which rusts because black chrome gives no protection
identity:
  formula: Electrodeposited chromium-containing black layer; the composition of the Harshaw CHROM-ONYX deposit is not stated in the sources read
  source: nasa-tm-x-71730
  where: Survey of Coatings for Solar Collectors (TM X-71730), description of black chrome and its plating; the bath is named as Harshaw CHROM-ONYX, and its chemistry is not given
tags:
  environments: []
  stresses:
    - high-temperature
    - humidity
  applications:
    - thermal-control
properties:
  - benchmark: solar_absorptance
    label: Solar absorptance, black chrome on commercial electroplated tin on steel
    value: 0.97
    unit: '-'
    scope: material
    conditions:
      substrate: commercially electroplated tin on steel, tin layer 0.001 cm (0.0004 in.), bright and uncorroded
      plating_time: approximately 2 minutes
      measurement: visible reflectance on a TAL Model 2164A alpha meter, absorptance calculated as 1 minus reflectance, accuracy plus or minus 0.02 units
    method: Measured reflectance, calculated absorptance, reported in NASA TM-73799
    status: ground
    source: nasa-tm-73799
    where: Summary of Results
  - benchmark: infrared_emittance
    label: Infrared emittance, black chrome on commercial electroplated tin on steel
    value: 0.06
    unit: '-'
    scope: material
    conditions:
      substrate: commercially electroplated tin on steel, tin layer 0.001 cm (0.0004 in.)
      plating_time: approximately 2 minutes
      measurement: infrared reflectance on a Gier-Dunkle DB-100 reflectometer, emittance calculated as 1 minus reflectance, accuracy plus or minus 0.02 units
    method: Measured reflectance, calculated emittance, reported in NASA TM-73799
    status: ground
    source: nasa-tm-73799
    where: Summary of Results
  - benchmark: infrared_emittance
    label: Infrared emittance of as-received commercial tin on steel, before black chrome plating
    value: 0.06
    unit: '-'
    scope: material
    conditions:
      substrate: bright, uncorroded commercial electroplated tin on steel, as received
      state: before black chrome plating
    method: Measured on the tin-plated steel panels, reported in NASA TM-73799
    status: ground
    source: nasa-tm-73799
    where: Test Results and Discussion, paragraph on the emittance of the tin on steel
  - benchmark: solar_absorptance
    label: Solar absorptance, black chrome, NASA survey Table 1
    value: 0.9
    unit: '-'
    scope: material
    conditions:
      basis: characteristic absorptance integrated over the solar spectrum, as printed in the table
      substrate: not stated in the table
      ceramic_enamel_row: 0.9 absorptance, 0.5 emittance
      alkyd_enamel_row: 0.9 absorptance, 0.9 emittance
    method: Table value from NASA survey TM X-71730, reflectance measured by the authors
    status: ground
    source: nasa-tm-x-71730
    where: Table 1 (Cost of Coatings for Solar Collectors), Black Chrome row
  - benchmark: infrared_emittance
    label: Infrared emittance, black chrome, NASA survey Table 1
    value: 0.1
    unit: '-'
    scope: material
    conditions:
      basis: characteristic infrared emittance, as printed in the table
      substrate: not stated in the table
    method: Table value from NASA survey TM X-71730, emittance calculated from measured reflectance
    status: ground
    source: nasa-tm-x-71730
    where: Table 1 (Cost of Coatings for Solar Collectors), Black Chrome row
  - benchmark: solar_absorptance
    label: Solar absorptance of black chrome on electroplated nickel, background value
    value: 0.95
    unit: '-'
    scope: material
    conditions:
      substrate: electroplated nickel
      wavelengths: 0.35 to 2.0 µm
      basis: approximate value stated in the introduction; the scanned copy renders its approximation sign poorly
    method: Stated in NASA TM-81385 as background for black chrome; not a new measurement in that memo
    status: ground
    source: nasa-tm-81385
    where: Introduction, first paragraph
  - benchmark: infrared_emittance
    label: Infrared emittance of black chrome on electroplated nickel, background value
    value: 0.1
    unit: '-'
    scope: material
    conditions:
      substrate: electroplated nickel
      wavelengths: 2.0 to 15 µm
      basis: approximate value stated in the introduction; the scanned copy renders its approximation sign poorly
    method: Stated in NASA TM-81385 as background for black chrome
    status: ground
    source: nasa-tm-81385
    where: Introduction, first paragraph
  - benchmark: max_service_temp
    label: Temperature above which black chrome loses absorptance irreversibly
    value: 300
    unit: degC
    scope: material
    conditions:
      atmosphere: air or vacuum
      effect: absorptance decreases irreversibly to 0.85 or less, with no significant change in emittance
    method: Statement in NASA TM-81385, based on the authors' heating tests of black chrome
    status: ground
    source: nasa-tm-81385
    where: Introduction, paragraph beginning 'It is important to have high absorptance and low emittance for concentrating collectors'
  - benchmark: solar_absorptance
    label: Solar absorptance of black chrome after heating above 300 degC
    value: 0.85
    bound: upper
    unit: '-'
    scope: material
    conditions:
      state: after exposure above 300 degC in air or in vacuum
      note: NASA states 0.85 or less; the emittance does not change significantly
    method: Statement in NASA TM-81385
    status: ground
    source: nasa-tm-81385
    where: Introduction, paragraph on high-temperature loss of absorptance
  - benchmark: solar_reflectance
    label: Solar reflectance, black chrome on dull nickel
    value: 0.077
    unit: '-'
    scope: material
    conditions:
      coating: black chrome on dull nickel, rough underlayer
      integration: solar spectrum for air mass 2
      wavelengths: 0.35 to 2.1 µm
      plating: Harshaw CHROM-ONYX at 24 volts and 2150 A/m2 (200 A/ft2) for 3 minutes; survey example of one minute at 1937 A/m2 (180 A/ft2) over dull nickel
      measurement: total diffuse reflectance, Cary 14 spectrophotometer, magnesium oxide standard
    method: Measured reflectance integrated over the solar spectrum, reported in NASA TM X-3136
    status: ground
    source: nasa-tm-x-3136
    where: Results, paragraph on figure 1 (values integrated over the solar spectrum for air mass 2)
  - benchmark: infrared_reflectance
    label: Infrared reflectance, black chrome on dull nickel
    value: 0.92
    unit: '-'
    scope: material
    conditions:
      coating: black chrome on dull nickel
      integration: black-body spectrum at 1210 degC (2500 F), 3 to 15 µm
      measurement: Willey-318-S spectrophotometer, evaporated gold standard
    method: Measured reflectance integrated over a black-body spectrum, reported in NASA TM X-3136
    status: ground
    source: nasa-tm-x-3136
    where: Summary, paragraph after the solar reflectance values
  - benchmark: absorptance_emittance_ratio
    label: Ratio of absorptance to emittance, black chrome on dull nickel
    value: 10.9
    unit: '-'
    scope: material
    conditions:
      coating: black chrome on dull nickel
      comparison: bright-nickel black chrome on 0.75 and 2.5 µm surfaces gave 7.8 and 6.6; black nickel samples gave 13.8 and 8.0; black paint gave 1.00
    method: Ratio calculated by NASA from measured reflectances, printed in NASA TM X-3136
    status: ground
    source: nasa-tm-x-3136
    where: Summary, paragraph on ratios of absorptance to emissivity
  - benchmark: solar_absorptance
    label: Mean solar absorptance, sample 6, electrodeposited black chromium
    value: 94.6
    unit: '%'
    scope: material
    conditions:
      process: electrodeposited black chromium from a bath of 274 g/l chromium trioxide and 0.854 g/l hexafluorosilicic acid, 5 V, 5 cm anode-cathode distance, 5 min
      wavelengths: 220 to 1400 nm
      note: a different process from Harshaw black chrome
    method: Absorptance from measured reflectance, reported in an open-access 2019 paper
    status: ground
    source: msrm-2019
    where: Section 3.1 (Figure 3) and the Conclusion
  - benchmark: solar_absorptance
    label: Maximum solar absorptance, sample 6, electrodeposited black chromium
    value: 96
    unit: '%'
    scope: material
    conditions:
      process: electrodeposited black chromium from a bath of 274 g/l chromium trioxide and 0.854 g/l hexafluorosilicic acid, 5 V, 5 cm anode-cathode distance, 5 min
      wavelengths: 220 to 1400 nm
      note: a different process from Harshaw black chrome
    method: Maximum absorptance from measured reflectance, reported in an open-access 2019 paper
    status: ground
    source: msrm-2019
    where: Section 3.1 (text on sample 6 maximum) and the Conclusion
corrosion:
  - environment: Steel substrate with black chrome plated straight onto it
    headline: Black chrome gives steel no rust protection, so a nickel plate goes under it.
    effect: NASA states that when black chrome is used on steel, the steel is first plated with nickel, both to produce low emittance and to prevent the steel from rusting, since the black chrome provides no such protection.
    rating: moderate
    conditions:
      basis: statement in the NASA survey; no rust test, duration or humidity level is reported
    source: nasa-tm-x-71730
    where: Introduction, paragraph on black chrome on steel
  - environment: Humid air and sunlight
    headline: NASA reports that black chrome is not affected by sunlight or humid air.
    effect: NASA states that black chrome is an inorganic coating and so is not susceptible to photodegradation, and that it is not susceptible to oxidation or degradation in humid atmospheres.
    rating: none
    conditions:
      basis: qualitative statement; no exposure test, duration or humidity level is given
    source: nasa-tm-x-3136
    where: Introduction, paragraph beginning 'Other necessary properties of a practical solar selective coating'
  - environment: Air or vacuum above 300 degC
    headline: Above 300 degC, black chrome loses absorptance irreversibly, in air or in vacuum.
    effect: NASA reports that black chrome irreversibly decreases in absorptance to 0.85 or less above 300 degC in either air or vacuum, with no significant change in emittance. This is why NASA sought a higher-temperature coating, based on black cobalt oxide.
    rating: moderate
    conditions:
      temperature: above 300 degC
      atmosphere: air or vacuum
    source: nasa-tm-81385
    where: Introduction, paragraph on high-temperature loss of absorptance
  - environment: Long-term durability in service (qualitative ranking)
    headline: NASA's durability table rates black chrome as stable.
    effect: Table 2 of the NASA survey rates black chrome durability as Stable, while black nickel is rated Destroyed by moisture and black copper Patinates with moisture. The survey adds that black chrome is matched only by ceramic enamel in durability and wide availability.
    rating: low
    conditions:
      basis: qualitative ranking from limited durability data, with no test duration or humidity level stated
    source: nasa-tm-x-71730
    where: Table 2 (Durability of Coatings for Solar Collectors) and the paragraph after Table 1
risks:
  hazards:
    - text: 'PubChem''s aggregated GHS record for chromium metal (CID 23976) lists H317 (20.7% of reports): May cause an allergic skin reaction, with signal word Danger. The same record says it does not meet GHS hazard criteria for 50% (1202 of 2404) of reports.'
      ghs:
        - H317
      source: pubchem-chromium
      where: GHS Classification section, GHS Hazard Statements and Signal rows
    - text: 'PubChem''s GHS record for chromium trioxide (CID 14915) lists H271 (100% of reports): May cause fire or explosion; strong oxidizer, with signal word Danger.'
      ghs:
        - H271
      source: pubchem-cro3
      where: GHS Classification section, GHS Hazard Statements and Signal rows
    - text: The 2019 open paper's electrodeposition bath for black chromium contains 274 g/l of chromium trioxide (CrO3) and 0.854 g/l of hexafluorosilicic acid. The paper gives no hazard statement for either compound. The Harshaw CHROM-ONYX bath used by NASA is not published, so its hazards are not known.
      source: msrm-2019
      where: Experimental bath composition in the text (bath of 274 g/l chromium trioxide)
  failure_risks:
    - mode: Loss of solar absorptance above 300 degC
      trigger: Heating black chrome in air or in vacuum above 300 degC
      consequence: Absorptance falls irreversibly to 0.85 or less, with no significant change in emittance.
      severity: moderate
      source: nasa-tm-81385
      where: Introduction, paragraph on high-temperature loss of absorptance
    - mode: Rust on steel without a nickel underplate
      trigger: Black chrome plated straight onto steel
      consequence: NASA states black chrome gives no rust protection, so the steel rusts.
      severity: moderate
      source: nasa-tm-x-71730
      where: Introduction, paragraph on black chrome on steel
  handling:
    - text: Keep the coated surface below 300 degC in air or vacuum; above that, absorptance falls irreversibly (NASA TM-81385).
      source: nasa-tm-81385
      where: Introduction, paragraph on high-temperature loss of absorptance
uses:
  - application: thermal-control
    device: Solar-thermal absorber, flat-plate solar collectors
    example: NASA chose black chrome for solar collectors because the wide use of black chrome as a durable decorative electroplated finish made it potentially low in cost, and it was already produced by the plating industry.
    source: nasa-tm-x-3136
    where: Introduction, paragraph on black chrome as a commercial electroplated finish
  - application: thermal-control
    device: Selective coating on concentrating solar collectors of lower multiplication ratio
    example: NASA reports that black chrome is used as a selective coating on concentrating collectors of lower multiplication ratio, but that it loses absorptance above 300 degC.
    source: nasa-tm-81385
    where: Introduction, paragraph on concentrating collectors
supply:
  - subject: Chromium
    producers:
      - country: South Africa
        share_percent: 45.1
        year: 2025
      - country: Turkey
        share_percent: 17.6
        year: 2025
      - country: Kazakhstan
        share_percent: 13.7
        year: 2025
      - country: India
        share_percent: 5.9
        year: 2025
    critical_lists: []
    recycling: 'USGS: recycled chromium, contained in reported stainless-steel scrap receipts, accounted for 21% of apparent consumption in 2025.'
    substitutes:
      - 'USGS: chromium has no substitute in stainless steel, the leading end use, or in superalloys, the major strategic end use.'
    source: usgs-mcs2026-chromium
    where: World Mine Production and Reserves table, 2025e (mine production in chromium content, thousand t; shares calculated by Space Mushroom against the rounded world total of 51,000); Recycling; Substitutes. Critical-list status is left out because no list page was checked for this profile.
documents:
  - title: 'NASA TM-73799: Black chrome on commercially electroplated tin as a solar selective coating (McDonald)'
    type: report
    url: https://ntrs.nasa.gov/api/citations/19780007619/downloads/19780007619.pdf
    year: 1977
  - title: 'NASA TM X-3136: Refinement in black chrome for use as a solar selective coating (McDonald; accession 75N12329)'
    type: report
    url: https://ntrs.nasa.gov/api/citations/19750004257/downloads/19750004257.pdf
    year: 1975
  - title: 'NASA TM X-71730: Survey of coatings for solar collectors (McDonald)'
    type: report
    url: https://ntrs.nasa.gov/api/citations/19750015917/downloads/19750015917.pdf
    year: 1974
  - title: 'NASA Tech Brief B75-10067: Survey of coatings for solar collectors'
    type: report
    url: https://ntrs.nasa.gov/api/citations/19750000067/downloads/19750000067.pdf
    year: 1975
  - title: 'NASA TM-81385: Preliminary study of a solar selective coating system using black cobalt oxide for high temperature solar collectors'
    type: report
    url: https://ntrs.nasa.gov/api/citations/19800009891/downloads/19800009891.pdf
    year: 1980
  - title: 'Selective solar surface based on black chromium: influence of electrodeposition parameters in the absorption of surfaces (open access)'
    type: paper
    url: https://www.scielo.br/j/mr/a/sFz44LPzS43Sm4WPQpGsrsC/?lang=en
    year: 2019
  - title: 'USGS Mineral Commodity Summaries 2026: Chromium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-chromium.pdf
    year: 2026
  - title: 'PubChem CID 23976: Chromium, GHS Classification'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23976/JSON?heading=GHS+Classification
  - title: 'PubChem CID 14915: Chromium Trioxide, GHS Classification'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/14915/JSON?heading=GHS+Classification
gaps:
  - No flight or space-environment result for black chrome was found; the tests in the sources are ground tests (laboratory reflectance and heating).
  - The composition of the commercial Harshaw CHROM-ONYX deposit is not stated in any source read in this run, so the recipe gives only chromium as the metal and no share of metal, oxide or other compounds.
  - No safety data sheet was read for the Harshaw CHROM-ONYX bath, whose composition is not published. The hazards entries use PubChem GHS records for chromium metal (CID 23976) and chromium trioxide (CID 14915), the bath component named in the 2019 open paper, not the Harshaw product itself.
  - Chromium's crustal abundance and its status on the USGS 2025 critical-minerals list and the EU critical raw materials list were not read on a page in this run; critical_lists is empty.
  - Plating current density in NASA TM-73799 is garbled in the copy read (1.5 and 21.5 amps/m2 both appear); it is not used.
  - NASA TM X-3136 prints 0.064 in its summary and 0.060 in its body for bright-nickel black chrome on a 2.5 micrometre surface; neither value is used. The dull-nickel value of 0.077 is printed the same way in both places.
  - Table 1 cost figures in the NASA survey are printed without a unit; they are not used.
  - NASA TM-81385 prints its background absorptance and emittance (0.95 and 0.1) in a scanned copy with a garbled approximation sign; they are recorded as approximate values.
  - The 2019 open paper describes a different process (electrodeposited black chromium from a chromium trioxide bath on a different substrate), not the Harshaw black chrome process. Its substrate grade and emittance are not in the fetched text.
  - Wikipedia's chrome plating page does not cover black chrome; no discoverer, lab date or history beyond the NASA statements was found in a fetched page.
  - Property names solar_absorptance, infrared_emittance, solar_reflectance, infrared_reflectance and absorptance_emittance_ratio are not in spores/property-canon.yaml; they are short snake_case names for properties the canon does not list.
  - No image was fetched or checked for licence, so the media section is omitted.
  - 'Designations (UNS, EN and similar) are not applicable: black chrome is a plating finish, not a standard grade.'
sources:
  nasa-tm-73799:
    title: Black chrome on commercially electroplated tin as a solar selective coating (NASA TM-73799, ERDA/NASA 1060-77/1)
    id: NASA TM-73799; NTRS 19780007619
    url: https://ntrs.nasa.gov/api/citations/19780007619/downloads/19780007619.pdf
    year: 1977
    kind: report
    license: public domain (NASA)
  nasa-tm-x-3136:
    title: Refinement in black chrome for use as a solar selective coating (NASA TM X-3136)
    id: NASA TM X-3136; NTRS 19750004257 (accession 75N12329)
    url: https://ntrs.nasa.gov/citations/19750004257
    year: 1975
    kind: report
    license: public domain (NASA)
  nasa-tm-x-71730:
    title: Survey of coatings for solar collectors (NASA TM X-71730, presented at the 1974 NSF workshop on solar collectors)
    id: NASA TM X-71730; NTRS 19750015917
    url: https://ntrs.nasa.gov/api/citations/19750015917/downloads/19750015917.pdf
    year: 1974
    kind: report
    license: public domain (NASA)
  nasa-tech-brief-b75:
    title: 'NASA Tech Brief B75-10067: Survey of coatings for solar collectors'
    id: NASA Tech Brief B75-10067; NTRS 19750000067
    url: https://ntrs.nasa.gov/api/citations/19750000067/downloads/19750000067.pdf
    year: 1975
    kind: report
    license: public domain (NASA)
  nasa-tm-81385:
    title: Preliminary study of a solar selective coating system using black cobalt oxide for high temperature solar collectors (NASA TM-81385)
    id: NASA TM-81385; NTRS 19800009891; N80-18156
    url: https://ntrs.nasa.gov/api/citations/19800009891/downloads/19800009891.pdf
    year: 1980
    kind: report
    license: public domain (NASA)
  msrm-2019:
    title: 'Selective solar surface based on black chromium: influence of electrodeposition parameters in the absorption of surfaces'
    id: doi:10.1590/1980-5373-MR-2018-0625 (Materials Research 22(2))
    url: https://www.scielo.br/j/mr/a/sFz44LPzS43Sm4WPQpGsrsC/?lang=en
    year: 2019
    kind: paper
    license: open access (SciELO); check the journal licence before reuse
  nist-cr:
    title: NIST Atomic Weights and Isotopic Compositions for chromium (element 24, symbol Cr)
    id: NIST standard atomic weight 51.9961(6); page accessed 2026-11-01
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Cr&all=on&ascii=html
    kind: database
    license: public domain (NIST)
  usgs-mcs2026-chromium:
    title: Mineral Commodity Summaries 2026, Chromium
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-chromium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  pubchem-chromium:
    title: 'PubChem CID 23976: Chromium, GHS Classification (aggregated ECHA C&L and company reports)'
    id: PubChem CID 23976
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23976/JSON?heading=GHS+Classification
    kind: database
    license: public domain (NIH, PubChem)
  pubchem-cro3:
    title: 'PubChem CID 14915: Chromium Trioxide, GHS Classification (aggregated ECHA C&L and company reports)'
    id: PubChem CID 14915
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/14915/JSON?heading=GHS+Classification
    kind: database
    license: public domain (NIH, PubChem)
license: CC-BY-4.0
updated: '2026-11-01'
review:
  status: draft
  method: assistant
  checked_values: 14
  unreachable: 1
  caveats: 3
  note: Written by an AI assistant on 2026-11-01 from NASA reports, an open 2019 paper and a USGS summary read in this run. PubChem GHS records for chromium (CID 23976) and chromium trioxide (CID 14915) were read for the hazards entries; no PubChem numeric property value is used. Wikipedia's black chrome content was empty. Caveats are listed in gaps.
story:
  recipe:
    line: Black chrome is an electroplated chromium layer. NASA's survey says the commercial deposit is a proprietary mixture from the Harshaw Chemical Company, plated over a nickel underlayer on steel. Its exact composition is not stated in the sources read. The plating step, as NASA ran it, uses Harshaw CHROM-ONYX at 24 volts and 2150 A/m2 (200 A/ft2) for 3 minutes.
    parts:
      - name: Chromium
        symbol: Cr
        role: The metal the bath deposits. The sources read do not give the share of metal versus other compounds in the black layer.
  risk_groups:
    - title: For people
      level: 0
      verdict: Not assessed in this run
      lead: No safety data sheet was read for the black chrome bath or the finished coating, so no hazard class is given here.
      points:
        - label: The bath
          line: The Harshaw CHROM-ONYX bath was not checked against a safety data sheet. Check the supplier's data sheet before handling the bath.
        - label: The finished panel
          line: NASA describes the finished coating as an inorganic layer that is not susceptible to photodegradation or to degradation in humid air. No toxicity data were found for it.
    - title: If a coated surface overheats
      lead: These results come from laboratory heating tests, not from field incidents.
      points:
        - label: Above 300 °C
          line: NASA reports that above 300 °C, in air or vacuum, black chrome loses absorptance irreversibly, falling to 0.85 or less, with no significant change in emittance.
    - title: Substrate and handling
      points:
        - label: Steel
          line: Plate a nickel layer under black chrome on steel. NASA states that black chrome gives no rust protection, so the steel rusts without the nickel.
        - label: Tin substrate
          line: NASA found that bright, uncorroded commercial tin on steel gave reproducible solar selective properties when plated.
  why: Black chrome is a solar selective coating. It absorbs most of the sunlight that reaches it, and it radiates little heat in the infrared. NASA Lewis Research Center discovered the property. Because black chrome is already used as a decorative electroplate, the plating industry can apply it cheaply, which is why NASA considered it for solar collectors. The coating gives up absorptance above 300 °C, so it suits lower-temperature absorbers.
  uses:
    - where: Flat-plate solar collectors
      line: NASA chose black chrome for flat-plate solar collectors because it was already a durable decorative finish in the plating industry, which kept the cost down.
    - where: Concentrating collectors of lower concentration
      line: NASA reports black chrome as a selective coating on concentrating collectors of lower concentration, but its absorptance falls above 300 °C, so NASA later looked for a higher-temperature coating.
  can_do:
    - label: Sunlight absorption
      benchmark: solar_absorptance
      value: 0.97 on tin
      line: On commercial electroplated tin on steel, black chrome plated for about 2 minutes gave an absorptance of 0.97 (NASA TM-73799). A NASA survey table lists 0.9 for black chrome.
    - label: Infrared emittance
      benchmark: infrared_emittance
      value: 0.06 on tin
      line: The same test gave an emittance of 0.06 on tin, and the survey table lists 0.1. The two values differ because the substrates and the test methods differ.
    - label: Heat limit
      benchmark: max_service_temp
      value: 300 °C
      line: Above 300 °C, in air or vacuum, absorptance falls irreversibly to 0.85 or less (NASA TM-81385).
  compare: In the NASA survey table, black chrome, black copper and black nickel each show 0.9 absorptance and 0.1 emittance. Ceramic enamel shows 0.9 and 0.5, and alkyd enamel 0.9 and 0.9, so black chrome is far more selective than either enamel. In NASA's reflectance tests on dull nickel, black chrome gave an absorptance-to-emittance ratio of 10.9, against 13.8 and 8.0 for two samples of black nickel, and 1.00 for black paint. Black nickel is the closest rival in the survey, but NASA reported it as destroyed by moisture. Black chrome is rated stable.
  compare_rows:
    - label: Solar absorptance (survey Table 1)
      benchmark: solar_absorptance
    - label: Infrared emittance (survey Table 1)
      benchmark: infrared_emittance
    - label: Absorptance to emittance ratio (dull nickel)
      benchmark: absorptance_emittance_ratio
  handling:
    - Use bright, uncorroded tin-plated steel or a nickel underplate. Black chrome on bare steel rusts.
    - Keep the coated surface below 300 °C. Above that, absorptance falls irreversibly.
    - Tailor the plating current and time to the bath in use, as NASA notes for black chrome.
    - Plate black chrome over a roughened dull-nickel surface to raise visible absorptance, which NASA found roughly halves the visible reflectance.
  good_for:
    - Solar-thermal absorbers up to about 300 °C. NASA's survey table lists 0.9 absorptance and 0.1 emittance.
    - Low-cost production. NASA notes that black chrome is a common decorative electroplate, which keeps the cost potentially low.
  watch_out:
    - Loss of absorptance above 300 °C, in air or vacuum, to 0.85 or less.
    - No rust protection on steel. A nickel underlayer is needed.
    - The bath chemistry and the deposit composition are not published in the sources read, so a new bath needs its own safety check.
  verdict: Black chrome is a proven, low-cost solar absorber for temperatures up to about 300 °C, with a nickel underlayer on steel. Above 300 °C NASA's own later study moved to other coatings, so black chrome is a lower-temperature choice.