ASTM B136-23

Standard Test Method for Measurement of Stain Resistance of Anodic Coatings on Aluminum

ABSTRACT
This specification covers measurement of strain resistance of anodic coatings on aluminium and its alloys, that have undergone a sealing treatment and contact with an acidic solution, are stainproof or nonadsorptive with respect to dyes. The method comprises contacting the test area of the anodized specimen with nitric acid solution and, after rinsing and drying, applying a special dye solution followed by rinsing and rubbing the test area with pumice powder, drying, and visual examination of the test area for retention of dye stain. Coatings that exhibit no dye stain or change in color are considered to have passed the test. Reagent grade chemicals shall be used in all tests. A specified solution of nitric acid shall be prepared in distilled or deionized water. A specified volume of aluminium blue 2WL dye shall be dissolved in distilled or deionized water.
SIGNIFICANCE AND USE
3.1 This test method is intended to determine whether anodic oxide coatings on aluminum and its alloys have been properly sealed and as a result are resistant to absorbing dyes.
SCOPE
1.1 This test method is intended to determine whether anodic oxide coatings on aluminum and its alloys, that have undergone a sealing treatment and contact with an acid solution, are stainproof or nonadsorptive with respect to dyes.  
1.2 Coatings that have been properly sealed should be proof against adsorption of coloring materials and, hence, “nonstaining” in many types of service.  
1.3 This test method is applicable to anodic coatings intended for applications where they are exposed to the weather, or for protective purposes in corrosive media, and where resistance to staining is important.
Note 1: Performance in this test is predictive only of susceptibility to stain by dyes. It is not intended to be predictive of other factors in service performance such as pitting or general corrosion.
Note 2: For Aluminum Association Class I and II architectural anodic coatings that are sealed in solutions containing less than 15 ppm silicates or 3 ppm phosphates, the acid pretreatment may be omitted.  
1.4 In the case of coatings colored in deep shades, where estimation of the intensity of any residual dye stain is difficult, interpretation of the test is based on whether or not the original color has been affected by the action of the test.  
1.5 This test method is not applicable to:  
1.5.1 Chromic acid type anodic coatings.  
1.5.2 Anodic coatings on aluminum alloys containing more than 2 mass % Cu or 4.5 mass % Si.  
1.5.3 Anodic coatings that have been sealed only in dichromate solutions.  
1.5.4 Anodic coatings that have undergone a treatment to render them hydrophobic.  
1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this 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, health, and environmental 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.

General Information

• Status: Published
• Publication Date: 30-Apr-2023
• ICS: 25.220.20 - Surface treatment
• Technical Committee: B08 - Metallic and Inorganic Coatings
• Drafting Committee: B08.07 - Conversion Coatings

Overview

ASTM B136-23 is the internationally recognized standard for measuring the stain resistance of anodic coatings on aluminum and aluminum alloys. Developed by ASTM International, this test method evaluates whether anodic oxide coatings that have undergone appropriate sealing treatments resist dye staining after exposure to an acidic solution. The procedure is applicable to coatings intended for use in demanding environments-such as outdoor exposure and corrosive conditions-where nonstaining surface properties are crucial to performance and aesthetics.

Key Topics

• Stain Resistance Assessment: The core of the method is a controlled laboratory procedure involving nitric acid exposure, dye application, and abrasive cleaning, followed by a visual inspection for residual staining on the anodized aluminum surface.
• Sealing Effectiveness: The method is intended to evaluate the quality of sealing treatments applied to anodic coatings. Properly sealed anodic oxides are resistant to dye absorption, ensuring a “nonstaining” finish in typical service environments.
• Applicability and Limitations:
  • Relevant to anodic oxide coatings on aluminum and its alloys with standard sealing treatments.
  • Not applicable to chromic acid anodic coatings, coatings with high copper or silicon content, those sealed only in dichromate solutions, or coatings treated for hydrophobic properties.
  • For deeply colored coatings, results rely on assessing any alteration of the original color rather than visible dye stains.
• Chemical and Environmental Considerations: The standard prescribes the use of reagent-grade chemicals, specifically detailed instructions for preparing nitric acid and dye solutions, to ensure accuracy and reproducibility.
• Safety and Compliance: Users must consider relevant safety, health, and environmental practices as the test method does not address all potential risks involved.

Applications

ASTM B136-23 is widely used in industries where aluminum surfaces are subject to public view or aggressive service environments, including:

• Architectural Aluminum: Ensures long-lasting appearance in building components-window frames, doors, curtain walls-by verifying nonadsorptive properties that prevent unsightly dye stains.
• Transport and Aerospace: Maintains integrity and cleanliness of exterior components and structural parts exposed to weathering and chemical exposure.
• Consumer Products and Appliances: Validates stain resistance in colored or clear anodized finishes on kitchenware, furniture, and electronic enclosures.
• Quality Assurance: Used by manufacturers and third-party testing labs to certify and qualify anodized finishes according to international standards for stain resistance and sealing quality.

Related Standards

For comprehensive surface protection and finishing quality on aluminum alloys, consider referencing these associated standards:

• ASTM B117 - Standard Practice for Operating Salt Spray (Fog) Apparatus, for corrosion resistance testing.
• ASTM B580 - Standard Specification for Anodic Oxide Coatings on Aluminum.
• ISO 2143 - Anodizing of aluminum and its alloys-Measuring the comparative resistance of anodic oxidation coatings to staining by dye.
• ISO 7599 - Anodizing of aluminum and its alloys-General specifications for anodic oxide coatings on aluminum.

By following ASTM B136-23, industries can ensure that anodic coatings on aluminum maintain their functional and aesthetic qualities, providing robust stain resistance and supporting product reliability in diverse applications.

Standards Content (Sample)

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.
Designation: B136 − 23 Endorsed by American
Electroplaters’ Society
Endorsed by National
Association of Metal Finishers
Standard Test Method for
Measurement of Stain Resistance of Anodic Coatings on
Aluminum
This standard is issued under the fixed designation B136; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* 1.5.4 Anodic coatings that have undergone a treatment to
render them hydrophobic.
1.1 This test method is intended to determine whether
anodic oxide coatings on aluminum and its alloys, that have 1.6 The values stated in SI units are to be regarded as
undergone a sealing treatment and contact with an acid standard. No other units of measurement are included in this
solution, are stainproof or nonadsorptive with respect to dyes. standard.
1.7 This standard does not purport to address all of the
1.2 Coatings that have been properly sealed should be proof
safety concerns, if any, associated with its use. It is the
against adsorption of coloring materials and, hence, “nonstain-
responsibility of the user of this standard to establish appro-
ing” in many types of service.
priate safety, health, and environmental practices and deter-
1.3 This test method is applicable to anodic coatings in-
mine the applicability of regulatory limitations prior to use.
tended for applications where they are exposed to the weather,
1.8 This international standard was developed in accor-
or for protective purposes in corrosive media, and where
dance with internationally recognized principles on standard-
resistance to staining is important.
ization established in the Decision on Principles for the
NOTE 1—Performance in this test is predictive only of susceptibility to
Development of International Standards, Guides and Recom-
stain by dyes. It is not intended to be predictive of other factors in service
mendations issued by the World Trade Organization Technical
performance such as pitting or general corrosion.
Barriers to Trade (TBT) Committee.
NOTE 2—For Aluminum Association Class I and II architectural anodic
coatings that are sealed in solutions containing less than 15 ppm silicates
2. Summary of Test Method
or 3 ppm phosphates, the acid pretreatment may be omitted.
1.4 In the case of coatings colored in deep shades, where 2.1 The test method depends upon the observation that a
estimation of the intensity of any residual dye stain is difficult, nonsealed or poorly sealed anodic coating is attacked by acid
interpretation of the test is based on whether or not the original and easily colored by dye, while an adequately sealed coating
color has been affected by the action of the test. is not appreciably attacked and does not retain any dye stain.
1.5 This test method is not applicable to: 2.2 The test method comprises contacting the test area of the
1.5.1 Chromic acid type anodic coatings. anodized specimen with nitric acid solution and, after rinsing
1.5.2 Anodic coatings on aluminum alloys containing more and drying, applying a special dye solution followed by rinsing
than 2 mass % Cu or 4.5 mass % Si. and rubbing the test area with pumice powder, drying, and
1.5.3 Anodic coatings that have been sealed only in dichro- visual examination of the test area for retention of dye stain.
mate solutions. Coatings that exhibit no dye stain or change in color are
considered to have passed the test.
This test method is under the jurisdiction of ASTM Committee B08 on Metallic
3. Significance and Use
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.07 on
Conversion Coatings.
3.1 This test method is intended to determine whether
Current edition approved May 1, 2023. Published May 2023. Originally
anodic oxide coatings on aluminum and its alloys have been
approved in 1940. Last previous edition approved in 2018 as B136 – 84 (2018).
properly sealed and as a result are resistant to absorbing dyes.
DOI: 10.1520/B0136-23.
*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
B136 − 23
4. Reagents 5.4 Apply a drop of the dye solution to the test area and
allow it to remain there for 5 min 6 10 s. The temperature of
4.1 Purity of Reagents—Reagent grade chemicals shall be
the dye solution and of the test specimen shall be
used in all tests. Unless otherwise indicated, it is intended that
25 °C 6 5 °C.
all reagents shall conform to the specifications of the Commit-
tee on Analytical Reagents of the American Chemical Society,
5.5 Wash the test area thoroughly with running water, then
where such specifications are available. Other grades may be
rub it with pumice powder (NF or USP Fine Grade) and a
used, provided it is first ascertained that the reagent is of
clean cloth wet with water, and finally rinse with water and blot
sufficiently high purity to permit its use without lessening the
dry with a clean cloth. The temperature of the water shall be
accuracy of the determination.
25 °C 6 5 °C.
4.2 Nitric Acid Solution—Prepare a 40 6 5 mass % solution
NOTE 5—The pumice scrub removes seali
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
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: B136 − 84 (Reapproved 2018) B136 − 23 Endorsed by American
Electroplaters’ Society
Endorsed by National
Association of Metal Finishers
Standard Test Method for
Measurement of Stain Resistance of Anodic Coatings on
Aluminum
This standard is issued under the fixed designation B136; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope Scope*
1.1 This test method is intended to determine whether anodic oxide coatings on aluminum and its alloys, that have undergone a
sealing treatment and contact with an acid solution, are stainproof or nonadsorptive with respect to dyes.
1.2 Coatings that have been properly sealed should be proof against adsorption of coloring materials and, hence, “nonstaining”
in many types of service.
1.3 This test method is applicable to anodic coatings intended for applications where they are exposed to the weather, or for
protective purposes in corrosive media, and where resistance to staining is important.
NOTE 1—Performance in this test is predictive only of susceptibility to stain by dyes. It is not intended to be predictive of other factors in service
performance such as pitting or general corrosion.
NOTE 2—For Aluminum Association Class I and II architectural anodic coatings that are sealed in solutions containing less than 15 ppm silicates or 3
ppm phosphates, the acid pretreatment may be omitted.
1.4 In the case of coatings colored in deep shades, where estimation of the intensity of any residual dye stain is difficult,
interpretation of the test is based on whether or not the original color has been affected by the action of the test.
1.5 This test method is not applicable to:
1.5.1 Chromic acid type anodic coatings.
1.5.2 Anodic coatings on aluminum alloys containing more than 2 mass % Cu or 4.5 mass % Si.
1.5.3 Anodic coatings that have been sealed only in dichromate solutions.
1.5.4 Anodic coatings that have undergone a treatment to render them hydrophobic.
This test method is under the jurisdiction of ASTM Committee B08 on Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee B08.07 on
Conversion Coatings.
Current edition approved Oct. 1, 2018May 1, 2023. Published October 2018May 2023. Originally approved in 1940. Last previous edition approved in 20132018 as
B136 – 84 (2013). DOI: 10.1520/B0136-84R18. – 84 (2018). DOI: 10.1520/B0136-23.
*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
B136 − 23
1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this 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, health, and environmental 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.
2. Summary of Test Method
2.1 The test method depends upon the observation that a nonsealed or poorly sealed anodic coating is attacked by acid and easily
colored by dye, while an adequately sealed coating is not appreciably attacked and does not retain any dye stain.
2.2 The test method comprises contacting the test area of the anodized specimen with nitric acid solution and, after rinsing and
drying, applying a special dye solution followed by rinsing and rubbing the test area with pumice powder, drying, and visual
examination of the test area for retention of dye stain. Coatings that exhibit no dye stain or change in color are considered to have
passed the test.
3. Significance and Use
3.1 This test method is intended to determine whether anodic oxide coatings on aluminum and its alloys have been properly sealed
and as a result are resistant to absorbing dyes.
4. Reagents
4.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where
such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high
purity to permit its use without lessening the accuracy of the determination.
4.2 Nitric Acid Solution—Prepare a 40 6 5 mass % solution of nitric acid (HNO ) in distilled or deionized water.
NOTE 3—A convenient way is to carefully add one volume of 70 % HNO (sp gr 1.41 at 20°C) to an equal volume of water, while stirring, observing
the normal precautions for handling strong acids.
4.3 Special Dye Solution—Dissolve 1 g of aluminum blue 2LW dye in 50 mL of distilled or deionized water. The pH of the dye
test solution shall be adjusted to 5.0 6 0.5 and maintained at this value with a
...