ASTM E1791-96 (2021) PDF

Full title and description

Designation: E1791 −96 (Reapproved 2021) — Standard Practice for Transfer Standards for Reflectance Factor for Near‑Infrared Instruments Using Hemispherical Geometry. This practice describes acceptable transfer standards (pressed powder and sintered PTFE) and procedures for use with near‑infrared (NIR) spectrophotometers and reflectometers that employ hemispherical geometry.

Abstract

This practice establishes guidance for the preparation, selection, and use of rugged transfer standards whose reflectance factors are sufficiently stable and spectrally neutral in the near‑infrared (780–2500 nm) to transfer a reflectance scale between instruments. It covers common materials (pressed barium sulfate powders and sintered PTFE, including carbon‑black doped variants), typical reflectance ranges, and considerations for reproducibility, cleaning, and geometric behavior relative to an ideal diffuse reflector.

General information

• Status: Reapproved (active practice, originally approved 1996; reapproved 2021).
• Publication date: Current edition approved September 1, 2021 (reapproval of E1791−96).
• Publisher: ASTM International (Committee E13, Subcommittee E13.03).
• ICS / categories: 37.020 — Optical equipment; molecular spectroscopy / near‑infrared spectroscopy.
• Edition / version: E1791 −96 (Reapproved 2021) — originally adopted 1996, current reapproval 2021.
• Number of pages: 4 pages (concise practice).

Scope

This practice covers procedures for the preparation and use of acceptable transfer standards for near‑infrared spectrophotometers using hemispherical geometry. It provides guidance on the types of materials suitable as transfer standards (pressed powder plaques and sintered PTFE, including carbon‑black doped variants), their typical spectral behavior across the NIR region (approximately 780–2500 nm), and limitations related to geometric distribution of reflected radiance and mechanical ruggedness. It does not address laboratory primary absolute reflectance calibrations (which are covered by separate CIE guidance) nor all safety concerns associated with use.

Key topics and requirements

• Definition and selection of transfer standards suitable for NIR hemispherical measurements (pressed BaSO4 powders; sintered PTFE; carbon‑black doped PTFE).
• Typical spectral reflectance characteristics and reproducibility expectations across 780–2500 nm.
• Preparation and handling procedures to preserve stability (resurfacing, cleaning, contamination control).
• Considerations of geometric reflectance behavior versus an ideal perfect reflecting diffuser and impact on instrument comparisons.
• Assignment and transfer of reflectance factor values from absolute measurements to working transfer standards.
• Limitations of certain standard types (e.g., pressed powders are more fragile and contamination‑sensitive than sintered PTFE).

Typical use and users

This practice is intended for national and industrial calibration laboratories, NIR instrument manufacturers, quality control and testing laboratories using reflectance instruments, and specialists who need to transfer a reflectance scale between instruments or establish routine calibrations with rugged transfer standards. Typical applications include instrument calibration checks, inter‑instrument comparisons, and establishing laboratory reference materials for routine NIR reflectance measurements.

Related standards

Referenced and related documents include: ASTM E259 (Practice for Preparation of Pressed Powder White Reflectance Factor Transfer Standards for Hemispherical and Bi‑Directional Geometries), ASTM E284 (Standard Terminology of Appearance), and CIE publications on absolute reflectance (for primary scale realization). Users should consult those documents for preparation details, terminology, and absolute calibration procedures.

Keywords

near‑infrared, NIR, reflectance factor, transfer standard, sintered PTFE, pressed powder, barium sulfate, hemispherical geometry, reflectometer, spectrophotometer, calibration, instrument intercomparison.

FAQ

Q: What is this standard?

A: ASTM E1791 −96 (Reapproved 2021) is a short practice that provides guidance on acceptable transfer standards and procedures for transferring reflectance factor scales for near‑infrared instruments using hemispherical geometry.

Q: What does it cover?

A: It covers the selection, preparation, use, and limitations of common transfer standards (pressed powder plaques and sintered PTFE materials) for NIR reflectance measurements, including typical spectral behavior, reproducibility, and geometric considerations relative to an ideal diffuser.

Q: Who typically uses it?

A: Calibration and testing laboratories, instrument manufacturers, quality control personnel, and researchers who perform NIR reflectance measurements and need reliable transfer standards to calibrate or compare instruments.

Q: Is it current or superseded?

A: The practice is the original E1791 adopted in 1996 and was reapproved in 2021 (designation E1791 −96 (2021)), so it is an active reapproved practice as of the 2021 edition. Users should verify later revisions or withdrawals with the publisher for the very latest status.

Q: Is it part of a series?

A: It is under the jurisdiction of ASTM Committee E13 (Molecular Spectroscopy and Separation Science) and relates to other ASTM practices on reflectance transfer standards and appearance terminology (for example, E259 and E284). It complements documents addressing absolute reflectance calibration methods such as CIE guidance.

Q: What are the key keywords?

A: near‑infrared, reflectance factor, transfer standard, PTFE, barium sulfate, hemispherical, calibration, spectrophotometer, reflectometer.