Optical Sphere Paint and a Working Standard of Reflectance

F. Grum, G. W. Luckey

Specially prepared barium sulfate powders and coatings of these powders with polyvinyl alcohol have been used as working standards of reflectance and for coating integrating spheres. These materials are satisfactory for use in the wavelength range 0.20–2.00 µ. Since the refractive index of barium sulfate is rather low, it is necessary to use fairly thick layers in order to obtain good results. The absolute value of luminous reflectance of the barium sulfate powder, described in this paper, is 0.995 ± 0.001, and that of the paint, when properly applied, is 0.992 ± 0.001. The spectral reflectance of this material is higher than that of magnesium oxide, particularly in the uv region of the spectrum. By using barium sulfate as reference standard and as a coating on the integrating spheres of spectrophotometers, it is now possible to measure spectral reflectance reliably in the uv region to 200 nm. Because the reflectance of barium sulfate paint is significantly greater than that of magnesium oxide in the shortwave region, there is a corresponding gain in instrument sensitivity when barium sulfate is used as a sphere coating and as a comparison material. © 1968 Optical Society of America.

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Materials
Curve 1
Temperature K: ~298 Wavelength Range, µm: 0.225-2.500 Geometry θ'ω': ~0° 2π Composition (weight percent), Specifications, and Remarks: Pressed powder; packing density ~2.3 g/cm³; specially purified grade; avg of 15 samples.
Curve 2
Temperature K: ~298 Wavelength Range, µm: 0.200-0.800 Geometry θ'ω': ~0° 2π Composition (weight percent), Specifications, and Remarks: Pressed powder; specially purified grade; crystal size 0.05-3.0 µm; packing density ~2.3 g/cm³; data extracted from smooth curve; relative to freshly smoked MgO.
Curve 3
Temperature K: ~298 Wavelength Range, µm: 0.225-2.500 Geometry θ'ω': ~0° 2π Composition (weight percent), Specifications, and Remarks: Specially purified grade; thickness 1.0 mm; binder, purified polyvinyl alcohol; PBR 100:1; poured onto flat aluminum substrate, air dried, and scraped with glass edge to assure flatness; avg of 15 samples.
Curve 1
Temperature, K: ~298 Wavelength Range, µm: 0.225-2.500 Geometry θ θ' ω': ~0° Reported Error, %: 2π Composition (weight percent), Specifications, and Remarks: BaSO₄ (specially purified grade) in purified polyvinyl alcohol binder (1.0 mm thick); PBR 100:1; poured onto flat aluminum substrate, air dried, and scraped with glass edge to assure flatness; avg of 15 samples.
Curve 2
Temperature, K: ~298 Wavelength Range, µm: 0.200-0.800 Geometry θ θ' ω': ~0° Reported Error, %: 2π Composition (weight percent), Specifications, and Remarks: BaSO₄ (specially purified grade) in purified polyvinyl alcohol binder (1.0 mm thick); PBR 100; poured onto flat aluminum substrate, air dried, scraped with glass edge to assure flatness; data extracted from smooth curve; measured relative to MgO.
Curve 3
Temperature, K: ~298 Wavelength Range, µm: 0.213-0.800 Geometry θ θ' ω': ~0° Reported Error, %: 2π Composition (weight percent), Specifications, and Remarks: Eastman White Reflectance paint, Distillation Products Industries (1.0 µm thick); BaSO₄ in polyvinyl alcohol binder; PBR 100:1; data extracted from smooth curve; measured relative to BaSO₄ pressed powder.
Curve 4
Temperature, K: ~298 Wavelength Range, µm: 0.225-2.500 Geometry θ θ' ω': ~0° Reported Error, %: 2π Composition (weight percent), Specifications, and Remarks: BaSO₄ (specially purified grade) in purified polyvinyl alcohol binder (1.0 mm thick); PBR 100:1; poured onto flat aluminum substrate, air dried, and scraped with glass edge to assure flatness; avg of 15 samples.
Curve 5
Temperature, K: ~298 Wavelength Range, µm: 0.200-0.800 Geometry θ θ' ω': ~0° Reported Error, %: 2π Composition (weight percent), Specifications, and Remarks: BaSO₄ (specially purified grade) in purified polyvinyl alcohol binder (1.0 mm thick); PBR 100; poured onto flat aluminum substrate, air dried, scraped with glass edge to assure flatness; data extracted from smooth curve; measured relative to MgO.
Curve 6
Temperature, K: ~298 Wavelength Range, µm: 0.213-0.800 Geometry θ θ' ω': ~0° Reported Error, %: 2π Composition (weight percent), Specifications, and Remarks: Eastman White Reflectance paint, Distillation Products Industries (1.0 µm thick); BaSO₄ in polyvinyl alcohol binder; PBR 100:1; data extracted from smooth curve; measured relative to BaSO₄ pressed powder.