ASTM D2805 Standard Test Method for Hiding Power of Paints by Reflectometry

    What is ASTM D2805?

    ASTM D2805 is a standard test method for measuring paint hiding power by reflectometry. Technicians apply the paint as a film, an instrument measures how much light the film reflects over black and white backgrounds, and analysts calculate the spreading rate at which the film reaches a contrast ratio of 0.98. ASTM D2805 (Standard Test Method for Hiding Power of Paints by Reflectometry) results in absolute physical meaning without reference to a comparison paint standard. It covers air-dry coatings with Y tristimulus values greater than 15% and, with appropriate modification, also applies to baking finishes. Formulators and pigment manufacturers use it to test specification coatings and evaluate pigment hiding efficiency.

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    Get Certified ASTM D2805 Testing for Reliable Paint Hiding Power Data

    A paint with poor hiding power will require extra coats or a thicker film, and a hiding claim without instrument data leaves the buyer or supplier open to disputes of coverage and cost. Thus, buyers and suppliers need a measurement that doesn’t depend on who looks at the film. ASTM D2805 provides formulators and buyers with a standardized method of measuring hiding power by reflectometry, which enables wider opacity testing of coatings. The test results enable manufacturers to make informed decisions during paint formulation, pigment selection, and quality control.

    What is the Scope of the ASTM D2805 Standard?

    ASTM D2805 is a standard test method for determination of hiding power, without reference to a material paint standard, for air-dry coatings with Y tristimulus values greater than 15%. With appropriate modification, the method also tests baking finishes.

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    The scope of ASTM D2805 includes-

    • Material type: Air-dry paints and coatings with Y tristimulus values greater than 15%, and baking finishes with appropriate modification.
    • Purpose: Determining hiding power with maximum precision and minimum subjectivity, as in testing specification coatings or evaluating the hiding efficiency of pigments.
    • Properties evaluated: Hiding power, H₀.₉₈, defined as the spreading rate at a contrast ratio of 0.98, along with the scattering coefficient, S, and, optionally, the contrast ratio at a specified spreading rate.
    • Testing method: Technicians measure the reflectance of paint films on the required black glass panels and black-and-white hiding-power charts. Analysts use measurements to calculate hiding power and the scattering coefficient.
    • Results: Hiding power and scattering coefficient in square meters per liter (m²/L). The standard states values in SI units only.
    • Test limitations: The method covers coatings with Y tristimulus values greater than 15%, and baking finishes need appropriate modification before testing.
    • Use conditions: Technicians apply uniform films with an applicator and record the applicator clearance in micrometers (µm).
    • Applications: Specification coating tests, pigment hiding efficiency studies, paint formulation, and quality control.

    What are the Uses of ASTM D2805 Testing?

    ASTM D2805 gives formulators and pigment makers an instrument-based measure of how well a coating hides a background. Engineers use the numbers to compare coatings and pigments without relying on visual judgment. This test method-

    • Determines hiding power as the spreading rate at a contrast ratio of 0.98.
    • Calculates the scattering coefficient of the coating.
    • Reports the contrast ratio at a specified spreading rate when needed.
    • Evaluates the hiding efficiency of pigments.
    • Tests specification coatings with maximum precision and minimum subjectivity.
    • Supports paint formulation and quality control.
    • Works for baking finishes with appropriate modification.

    Which Materials Can Be Tested Under ASTM D2805?

    ASTM D2805 applies to air-dry coatings with Y tristimulus values greater than 15% and to baking finishes with appropriate modification. Technicians apply the paint to black glass panels and to black and white hiding power charts. Formulators commonly select this method for specification coatings and pigment hiding efficiency studies.

    Why is ASTM D2805 Important?

    Hiding power determines how much paint a surface needs before the background stops being visible. Visual checks are subjective, and they depend on how the paint is applied. ASTM D2805 replaces the subjectivity with reflectance measurements so that the result has an absolute physical meaning without comparison to a reference paint. That precision matters when a buyer tests a specification coating or a producer compares the efficiency of different pigments.

    ASTM D2805 Equipment and Sample Preparation Guide

    ASTM D2805 uses a reflectance-measuring instrument to determine the diffuse reflectance, or CIE Y tristimulus value, of paint films. The setup includes black glass panels, black-and-white hiding-power charts, glass slides, a precision balance, a film applicator, a template, and software for calculating hiding power.

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    Sample and Specimen DetailsTechnicians take a representative sample of the air-dry coating or of a baking finish when the method is suitably modified.
    Specimen PreparationTechnicians apply uniform paint films to black glass panels and to black and white hiding power charts with an applicator, then let the films dry.
    Specimen DimensionsBlack glass panels measure at least 200 × 200 mm and are approximately 6 mm thick. Glass slides are round or square plates with a minimum area of 40 cm². The film-application template defines an area of approximately 100 cm².
    Equipment and MaterialsThe equipment includes black glass panels, black-and-white hiding-power charts, glass slides, a balance accurate to 0.1 mg, a reflectance-measuring instrument, a film-area template, doctor-blade applicators, and computer software for the Kubelka–Munk calculations. The charts must have a black area with maximum reflectance of 1% and a white area with minimum reflectance of 78%; the white area must be non-fluorescent.

    Testing Procedures and Requirements for ASTM D2805

    This test standard specifies applying paint films to black glass and to black and white charts, measuring their reflectance, and calculating hiding power from the readings. The ASTM D2805 test method comprises the following steps-

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    Specimen PreparationTechnicians prepare the required black glass panels, black-and-white hiding-power charts, and glass slides. They ensure that the substrates are suitable for the specified reflectance measurements.
    Film ApplicationTechnicians make manual drawdowns using a smooth, uniform motion at approximately 6 cm/s. They use a 150 mm-wide doctor-blade applicator with a clearance of 50, 75, 100, 125, 150, 175, or 200 µm, as required, and record the clearance used.
    Film DryingTechnicians allow the trial drawdowns used for applicator selection to dry overnight before measuring their contrast ratios. For the subsequent test films, they follow the applicable drying and conditioning requirements of ASTM D2805.
    Reflectance MeasurementTechnicians measure the reflectance of each test area at a minimum of three locations, reading or estimating values to four decimal places and calculating the mean to the same precision. They place charts over a white surface and black glass panels over a black surface during measurements.
    Spreading Rate DeterminationAnalysts calculate the experimental spreading rate, Hₓ, in square meters per liter (m²/L), using the template area, paint nonvolatile content, liquid density, and dry-film weight.
    Density DeterminationAnalysts determine the liquid coating’s density in grams per milliliter (g/mL) per ASTM D1475. They use this value in the spreading-rate calculation.
    Nonvolatile Content Determination Analysts sandwich approximately 0.3 mL of paint between two previously weighed glass slides and squeeze it into a film approximately 45 mm in diameter. They weigh the slides with the paint, separate them, allow the films to dry, and weigh them again to determine the dry-film weight. They perform duplicate determinations and report the mean nonvolatile content as specified by the method.
    Applicator SelectionTechnicians make trial drawdowns on black-and-white charts using applicator clearances of 100, 150, and 200 µm. After allowing the films to dry overnight, they measure the contrast ratios and select an appropriate clearance to obtain a contrast ratio of 0.97 ± 0.01.
    Drawdowns on Glass and ChartsTechnicians use the selected applicator to prepare four drawdowns on black glass panels and four on black-and-white hiding-power charts. They retain sufficient uncoated white chart area to measure the substrate reflectance.
    CalculationAnalysts calculate the coating reflectivity, R∞, from the chart measurements and determine the scattering coefficient, S, using the reflectivity, black-glass film reflectance, and experimental spreading-rate data. They calculate hiding power, H₀.₉₈, at a contrast ratio of 0.98.
    Optional Contrast RatioWhen required, analysts calculate the contrast ratio, C, at a specified spreading rate, H꜀, using the calculated coating reflectivity and scattering coefficient.
    Reporting Analysts report hiding power, H₀.₉₈, reflectivity, R∞, scattering coefficient, S, and the applicator clearance. They also record the specified instrument information and other required worksheet results in accordance with ASTM D2805.

    ASTM D2805 Testing Process and Data Collection

    Technicians prepare black glass panels and black-and-white hiding-power charts, apply paint films using a controlled drawdown motion, and after drying, measure reflectance at a minimum of three locations on each test area. Analysts determine the paint’s density and nonvolatile content, calculate the experimental spreading rate, and use the reflectance measurements to determine coating reflectivity and the scattering coefficient. Analysts then calculate hiding power at a contrast ratio of 0.98 and report the required results.

    The image shows the ASTM D2805 sequence, from applying paint films to black glass panels and black and white charts through reflectance measurement to the calculation of hiding power.
    ASTM D2805 Hiding Power Testing Sequence by Reflectometry 

    Common Challenges and Troubleshooting

    Uneven film thickness shifts the spreading rate and the reflectance readings, so a technician should apply films at a steady applicator speed and check the film for streaks before measuring. Dust, fingerprints, or scratches on the film or the panel can change the reflectance, and a technician should therefore handle panels by their edges and keep them covered while drying. Drift in the reflectometer changes every Y tristimulus reading, so an analyst should check the instrument against its reference before each series. The method covers air-dry coatings with Y tristimulus values greater than 15%; baking finishes require appropriate modification.

    ASTM D2805 Analysis Results and Interpretation

    ASTM D2805 states results in SI units, and the standard includes no other units of measurement.

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    • The analyst reports hiding power, H₀.₉₈, as the spreading rate at a contrast ratio of 0.98 in square meters per liter (m²/L).
    • A contrast ratio of 0.98 is the defined endpoint for hiding-power measurement, but it does not represent visually complete hiding or guarantee the same contrast ratio at every wavelength.
    • The analyst reports the scattering coefficient, S, in the same units as spreading rate (m²/L).
    • The technician reports the applicator clearance in micrometers (µm).
    • The analyst reports the contrast ratio at a specified spreading rate as a dimensionless ratio when that option applies.
    • A higher H0.98 indicates that a coating covers more area per liter at the specified contrast ratio, assuming consistent test conditions. 
    • The engineer compares H₀.₉₈ and S across coatings or pigments tested under the same conditions.

    The ASTM D2805 pricing starts at $400-$450 per sample. However, final pricing depends on several factors, including the type and number of samples, specimen size, specimen preparation requirements, and any other specific condition requirements. We offer faster turnaround times for a rush fee. Please contact our team to understand more about your particular testing needs.

    What is the turnaround time for ASTM D2805?

    The standard turnaround time for this test is 2-3 weeks. However, turnaround time may vary depending on the samples being handled and the required test conditions. Please contact our team to understand more about your particular testing needs.

    Link to ASTM D2805

    FAQ

    How does ASTM D2805 measure hiding power?
    ASTM D2805 measures paint hiding power using reflectance measurements from films applied over black and white backgrounds. Analysts use these readings with coating data to calculate the spreading rate at which the film reaches a contrast ratio of 0.98. This provides an instrumental result without requiring a comparison paint.
    ASTM D2805 covers air-dry coatings with a Y tristimulus value greater than 15%. The test method can also be used for baking finishes when the necessary adaptations are made.
    ASTM D2805 reports hiding power and the scattering coefficient in square meters per liter (m²/L). The method uses SI units, and the applicator clearance is recorded in micrometers (µm).
    ASTM D2805 specifies black glass panels measuring at least 200 × 200 mm, with a thickness of approximately 6 mm. Technicians should also record the applicator clearance used to prepare the paint films.
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    Updated on October 23, 2026

    Davis Scott
    About Author
    Davis Scott
    Davis Scott is an Electrical and Electronics Engineer specializing in multidisciplinary validation, quality assurance, and comprehensive electro-mechanical testing.
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