ASTM G24-21

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it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: G24 − 13 G24 − 21
Standard Practice for
Conducting Exposures to Daylight Filtered Through Glass
This standard is issued under the fixed designation G24; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*
1.1 This practice evaluates the resistance of nonmetallic materials to solar radiation describes procedures for conducting exposures
of various materials to daylight filtered through glass in passively ventilated and non-vented enclosures. For exposures in under
glass enclosures with forced air circulation, refer to Practice G201.
1.1.1 This practice is not intended for corrosion testing of bare metals.
1.2 For direct exposures, refer to Practice G7.
1.3 This practice is limited to the method of conducting the exposures. The preparation of test specimens and evaluation of results
are covered in various standards for the specific materials.
1.4 Exposure conducted according to this practice can use two types of exposure cabinets.
1.4.1 Type A—A cabinet that allows passive ventilation of specimens being exposed behind glass.
1.4.2 Type B—Enclosed cabinet with exterior painted black that does not provide for ventilation of specimens exposed behind
glass. Exposures conducted using a Type B cabinet are typically referred to as “black box under glass exposures.”
1.5 Type A exposures of this practice are technically similar to Method B of ISO 877-2.
1.6 Units—The values stated in SI units are to be regarded as the standard. The inch-pound units values given in parentheses are
for information only.after SI units are provided for information only and are not considered standard.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.8 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
This practice is under the jurisdiction of ASTM Committee G03 on Weathering and Durability and is the direct responsibility of Subcommittee G03.02 on Natural and
Environmental Exposure Tests.
Current edition approved June 1, 2013Dec. 1, 2021. Published July 2013December 2021. Originally approved in 1973. Last previous edition approved in 20052013 as
G24 – 05.G24 – 13. DOI: 10.1520/G0024-13.10.1520/G0024-21.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G24 − 21
2. Referenced Documents
2.1 ASTM Standards:
C1036 Specification for Flat Glass
D3424 Practice for Evaluating the Relative Lightfastness and Weatherability of Printed Matter (Withdrawn 2020)
D4303 Test Methods for Lightfastness of Colorants Used in Artists’ Materials
D6901 Specification for Artists’ Colored Pencils
E824 Test Method for Transfer of Calibration From Reference to Field Radiometers
E903 Test Method for Solar Absorptance, Reflectance, and Transmittance of Materials Using Integrating Spheres
E1084 Test Method for Solar Transmittance (Terrestrial) of Sheet Materials Using Sunlight
G7 Practice for Natural Weathering of Materials
G113 Terminology Relating to Natural and Artificial Weathering Tests of Nonmetallic Materials
G173G147 Tables for Reference Solar Spectral Irradiances: Direct Normal and Hemispherical on 37° Tilted SurfacePractice for
Conditioning and Handling of Nonmetallic Materials for Natural and Artificial Weathering Tests
G177 Tables for Reference Solar Ultraviolet Spectral Distributions: Hemispherical on 37° Tilted Surface
G201 Practice for Conducting Exposures in Outdoor Glass-Covered Exposure Apparatus with Air Circulation
2.2 Other Documents:ISO Standards:
WMO Guide to Meteorological Instruments and Methods of Observation WMO No. 8, Seventh Edition.
ISO 105 B01 Textiles—Tests for Colour Fastness, International Standards Organization, Geneva, Switzerland.
ISO 877-1877-2 Plastics – Methods of Exposure to Solar Radiation – Part 1: General Guidance2: Direct Weathering and
Exposure Behind Window Glass
ISO 877–2 Plastics – Methods of Exposure to Solar Radiation – Part 2: Direct Weathering and Exposure Behind Window Glas
AATCC TM 16, Option 6ISO 9060:2018 Colorfastness to Light, DaylightSolar Energy – Specification and Classification of
Instruments for Measuring Hemispherical Solar and Direct Solar Radiation
AATCC Test Method 16.1-2012 Colorfastness to Light: Outdoor
2.3 Other Document:
WMO Guide to Meteorological Instruments and Methods of Observation WMO No. 8, 2014 Edition (2017).
3. Terminology
3.1 Definitions:
3.1.1 The definitions contained in Terminology G113 are applicable to this practice.
4. Significance and Use
FIG. 1 a and 1b Typical Passively-Ventilated Under Glass Exposure Cabinet, Type A
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from World Meteorological Organization (WMO), 7bis, avenue de la Paix, Case Postale No. 2300, CH-1211 Geneva 2, Switzerland, http://www.wmo.int.
The last approved version of this historical standard is referenced on www.astm.org.Available from International Organization for Standardization (ISO), ISO Central
Secretariat, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva, Switzerland, https://www.iso.org.
G24 − 21
FIG. 2 Typical Non-Ventilated Enclosed Under Glass Exposure Cabinet, Type B (Black Box Under Glass)
4.1 Since solar radiation, air temperature, relative humidity, and the amount and kind of atmospheric contaminants vary
continuously, results from exposures based on elapsed time may will sometimes differ. The variations in the results may will
usually be minimizedreduced by timing the exposures in terms of:
4.1.1 One or more environmental parameters such as solar radiant exposure, or
4.1.2 A predefined property change of a weathering reference specimen with known performance.
4.2 Variations in temperature, moisture, and atmospheric contaminants can have a significant effect on the degradation caused by
solar radiation. In addition, exposures conducted at different times of the year can cause large differences in the rate of degradation.
Different materials maygenerally have different sensitivities to heat, moisture, and atmospheric contaminants, which may and this
could explain differences in rankings of specimens exposed to equivalent solar radiant exposure when other environmental
conditions vary.
4.3 Since the method of mounting may has an influence on the temperature and other parameters during exposure of the specimen,
there should be a mutual understanding shall be agreement between contractual parties as to the method of mounting the specimen
for the particular exposure test under consideration.
4.4 There can be large are differences among various single strength window glasses in their transmittance in the 300 to 350 nm
region. For example, at 320 nm, the percent transmittance for seven different lots of single strength window glass ranged from 8.4
to 26.8 %. At 380 nm, the percent transmittance ranged from 84.9 % to 88.1 %.
4.5 Differences in UV transmittance between different lots of glass persist generally continue even after solarization. The largest
differences among window glasses in UV transmittance are in the spectral range of 300 to 320 nm.
4.6 This practice is best used to compare the relative performance of materials tested at the same time behind the same lot of glass.
Because of variability between lots of glass and between exposures conducted at different times of the year, comparing the amount
of degradation in materials exposed for the same duration or radiant exposure at separate times, or in separate fixtures using
different lots of glass, is not recommended.
4.7 It is strongly recommended that at least one control material with known performance be exposed with each test. The control
material should be of similar composition and construction. construction as the test specimen, and be chosen so that its failure
modes are the same as that of the material being tested. It is preferable to use two control materials, one with relatively good
durability, and one with relatively poor durability. IfWhen control materials are included as part of the test, they shall be used for
the purpose of comparing the performance of the test materials relative to the controls.
Ketola, W. D., and Robbins, J.S., III, “UV Transmission of Single Strength Window Glass,” Accelerated and Outdoor Durability Testing of Organic Materials, ASTM
STP 1202, Warren D. Ketola and Douglas Grossman, Eds., American Society for Testing and Materials, Philadelphia, 1994.
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4.8 There are other standards which describe exposures to glass filtered daylight. Six cited standards are D3424, D4303,D6901,
ISO 105-B01, ISO 877-1, ISO-877-2, AATCC TM 16C.
4.8 Because of the possibility that certain materials maywill outgas during exposure, exposure and potentially contaminate other
specimens, it is recommended that only similar materials be exposed in the same under glass cabinet at the same time.
5. Apparatus
5.1 Exposure Cabinet:
5.1.1 Type A—A glass-covered enclosure or cabinet of any convenient size, constructed to protect the specimens from rain. It
typically is constructed of metal or wood, and shall be open on the back or sides to allow ambient air to passively circulate over
the specimens (Fig. 1a and b).b show a typical glass cabinet empty, and with specimens, respectively).
5.1.2 Type B (Black Box Under Glass)—A glass-covered enclosure or cabinet of any convenient size. It shall be constructed of
corrosion resistant metal and be enclosed to prevent ambient air from circulating over specimens. Exterior non-glass surfaces that
will be irradiated shall be painted flat black. The interior shall remain unpainted (Fig. 2).
NOTE 1—For some exposures (for example, Method B of Test Methods D4303 or Method A of Specification D6901), a small fan is inserted into the Type
B enclosure to minimize condensation. For enclosures with forced air circulation, refer to Practice G201.
NOTE 2—The black box under glass enclosure is often used to simulate under glass exposures under conditions of high temperature, such as the interior
of an automobile. However, because black Black box under glass cabinets are enclosed, and air temperatures inside the cabinet may exceed 80°C80 °C
under conditions of high outside ambient air temperature and solar irradiance. In addition, significant Significant differences in air and specimen
temperatures can be experienced between upper and lower portions of the cabinet. Frequent temperature measurement and specimen repositioning may
be required to properly use this enclosure.
5.1.3 Unless otherwise specified, the glass cover shall be a piece of clear, non-laminated, transparent flat glass, greenhouse quality
Q4 or better as specified in sectionsubsection 4.1 of Specification C1036. Thickness shall be 2.0 to 3.2 mm.
5.1.3.1 In order to reduce variability of results due to changes in UV transmittance of glass, all new glass shall be exposed facing
the equator,for at least three months prior to using to expose specimens per this practice. Expose the new glass facing the equator
at any convenient exposure tilt angle within the range of 5 to 45°, according to Practice G7, or on an empty under glass exposure
cabinet, for at least three months prior to installation in test cabinets. cabinet.
5.1.3.2 After the three-month pre-exposure period, it is recommended that the spectral transmittance of representative samples
from each lot of glass be measured. Typically, “single strength” glass will have a transmittance of 10 to 20 % at 320 nm and at
least 85 % at wavelengths of 380 nm or higher after the three month pre-aging procedure. IfWhen transmittance of the glass is
measured, report the average for at least three pieces of the lot of glass being tested. Follow the instructions for measurement of
transmittance of solid samples recommended by the manufacturer of the UV-visible spectrophotometer used. IfWhen a
spectrophotometer with an integrating sphere is used, the measurements shall be performed in accordance with Test Method E903.
NOTE 3—Other standards describing exposures behind glass have different requirements for glass transmittance and do not require pre-aging.
NOTE 4—After the initial pre-aging period, the UV transmittance of window glass is suitable for at least 60 months of use. UV transmittance differences
between lots of glass persist during this time, however. Different lots of single-strength window glass can have different optical properties even ifwhen
purchased from the same manufacturer.
5.1.3.3 The exact history of each individual piece of glass is typically not tracked.
5.1.3.4 Wash the exterior surface of the glass cover every month, and month with soap and water, and the interior surface of the
glass cover every 3 months (or more frequently, ifas required) to remove dust particles and other undesirable deposits. Cleaning
the interior surface with solvents will be needed when outgassing products are seen, followed by washing with soap and water to
remove the cleaning agents. Remove the glass from the exposure frame when cleaning the interior surface.
5.1.4 The enclosure or cabinet shall be equipped with a rack which supports the specimens in a plane which is as close to parallel
to the glass. glass as practically possible. Whenever possible, the specimens should be are positioned such that the primary surface
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is supported at a distance of 75 6 25 mm (3 6 1 in.) behind the glass cover. Formed specimens with irregular dimensions maywill
require custom mounting with varying distances from the glass cover. In such cases, mount the test sample specimen so that the
surface of major interest is parallel to the glass cover at a distance of 75 6 25 mm (3 6 1 in.) behind the glass cover. The mounting
frame or plate shall be constructed of a material that is compatible with the test specimens. In order to minimize shadowing from
the top and sides of the cabinet, the usable exposure area under the glass shall be limited to that of the glass cover reduced by twice
the distance from the cover to the specimens as shown in Fig. 3. The effective width of the specimen mounting area is L-4X and
the effective height of the mounting area is W-4X, where L is the width of the glass cover, W is the height of the glass cover, and
X is the distance between the glass cover and the specimens. For example, if the when the primary surfaces of the specimens are
75 mm below the glass, then all specimens shall be at least 150 mm from the top, or sides. Three bottom, or sides. Use one of
these three types of mounting frames or backings may be used.backings.
5.1.4.1 Unbacked or Open Mounting—Specimens are attached only at edges.
5.1.4.2 Expande
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