ASTM B556-90(2023)

Standard Guide for Measurement of Thin Chromium Coatings by Spot Test

SIGNIFICANCE AND USE
4.1 The thickness of a decorative chromium coating is often critical to its performance.  
4.2 This procedure is useful for an approximate determination when the best possible accuracy is not required. For more reliable determinations, the following methods are available: Methods B504, B568, and B588.  
4.3 This test assumes that the rate of dissolution of the chromium by the hydrochloric acid under the specified conditions is always the same.
SCOPE
1.1 This guide covers the use of the spot test for the measurement of thicknesses of electrodeposited chromium coatings over nickel and stainless steel with an accuracy of about ±20 % (Section 9). It is applicable to thicknesses up to 1.2 μm.2
Note 1: Although this test can be used for coating thicknesses up to 1.2 μm, there is evidence that the results obtained by this method are high at thicknesses greater than 0.5 μm.3 In addition, for coating thicknesses above 0.5 μm, it is advisable to use a double drop of acid to prevent depletion of the test solution before completion of the test.  
1.2 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.  
1.3 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: 31-Oct-2023
• ICS: 25.220.40 - Metallic coatings
• Technical Committee: B08 - Metallic and Inorganic Coatings
• Drafting Committee: B08.10 - Test Methods

Relations

• Replaces: ASTM B556-90(2018) - Standard Guide for Measurement of Thin Chromium Coatings by Spot Test
• Effective Date: 01-Nov-2023
• Referred By: ASTM B604-91(2019) - Standard Specification for Decorative Electroplated Coatings of Copper Plus Nickel Plus Chromium on Plastics
• Effective Date: 01-Nov-2023

Overview

ASTM B556-90(2023): Standard Guide for Measurement of Thin Chromium Coatings by Spot Test provides a widely recognized procedure for estimating the thickness of electrodeposited chromium coatings, primarily over nickel and stainless steel substrates. This standard, developed by ASTM International, outlines the spot test method, which is particularly useful for rapid, approximate determination of chromium coating thickness where the highest accuracy is not required.

The spot test method is applicable to coatings up to 1.2 μm, though best results are achieved with coatings of 0.5 μm thickness or less. The guide also emphasizes the need for proper safety, health, and environmental practices when using chemical test solutions.

Key Topics

• Scope

  • Applicable to electrodeposited chromium coatings over nickel and stainless steel.
  • Measurement accuracy is approximately ±20%.
  • Suitable for coatings up to 1.2 μm, with optimal performance up to 0.5 μm.
  • For greater reliability and accuracy, other standardized methods like ASTM B504, B568, and B588 are recommended.
  • Developed in line with World Trade Organization Technical Barriers to Trade (TBT) principles.

• Measurement Principle

  • The test involves placing a drop of hydrochloric acid (or antimony trioxide-hydrochloric acid for stainless steel) on the coating.
  • The time taken for the acid to penetrate the chromium layer is measured.
  • The thickness of the coating is proportional to the penetration time, allowing an estimate of the coating thickness.

• Preparation and Procedure

  • Test area must be cleaned and marked to ensure consistent results.
  • Specimens and solutions should be at controlled room temperature (16°C – 25°C).
  • Measurement is performed using a stopwatch for precise timing.

• Limitations

  • Results may be less accurate for coatings thicker than 0.5 μm.
  • Assumes consistent rate of acid dissolution across samples.
  • Not intended for applications requiring high precision or comprehensive quality control.

Applications

The ASTM B556 spot test method is utilized in various industries and quality control settings for:

• Decorative Chromium Coatings
  Ensures coatings on consumer goods, automotive parts, hardware, and appliances meet minimum performance requirements.
• Production Line Quality Checks
  Provides a quick, cost-effective means for routine monitoring of thin chromium layers during manufacturing.
• Field Inspections and Maintenance
  Allows inspectors to rapidly assess the presence and approximate thickness of chromium coatings on installed parts and structures.
• R&D and Failure Analysis
  Assists research teams in evaluating coating performance during development or when investigating coating failures.

While not a replacement for more precise methods, the spot test is valued for its speed and simplicity in environments where timely, approximate measurements suffice.

Related Standards

For users requiring higher accuracy or different testing methods, ASTM points to these related standards:

• ASTM B504: Test Method for Measurement of Thickness of Metallic Coatings by the Coulometric Method
• ASTM B568: Test Method for Measurement of Coating Thickness by X-Ray Spectrometry
• ASTM B588: Test Method for Measurement of Thickness of Transparent or Opaque Coatings by Double-Beam Interference

These standards provide more accurate or specific measurement techniques for metallic coating thickness, complementing the approximate results of the spot test method outlined in ASTM B556-90(2023).

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Keywords: chromium coating thickness measurement, spot test method, electrodeposited chromium, ASTM B556, decorative chromium, quality control, thin coatings, manufacturing standards.

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: B556 − 90 (Reapproved 2023)
Standard Guide for
Measurement of Thin Chromium Coatings by Spot Test
This standard is issued under the fixed designation B556; 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 Microscope Technique (Withdrawn 2016)
1.1 This guide covers the use of the spot test for the
3. Summary of Guide
measurement of thicknesses of electrodeposited chromium
3.1 A drop of hydrochloric acid (test solution) is deposited
coatings over nickel and stainless steel with an accuracy of
on the surface of the test specimen, and the time required for
about 620 % (Section 9). It is applicable to thicknesses up to
2 the hydrochloric acid to penetrate through the chromium
1.2 μm.
coating (penetration time) is measured. The coating thickness
NOTE 1—Although this test can be used for coating thicknesses up to
is proportional to this time.
1.2 μm, there is evidence that the results obtained by this method are high
at thicknesses greater than 0.5 μm. In addition, for coating thicknesses
4. Significance and Use
above 0.5 μm, it is advisable to use a double drop of acid to prevent
4.1 The thickness of a decorative chromium coating is often
depletion of the test solution before completion of the test.
critical to its performance.
1.2 This standard does not purport to address all of the
4.2 This procedure is useful for an approximate determina-
safety concerns, if any, associated with its use. It is the
tion when the best possible accuracy is not required. For more
responsibility of the user of this standard to establish appro-
reliable determinations, the following methods are available:
priate safety, health, and environmental practices and deter-
Methods B504, B568, and B588.
mine the applicability of regulatory limitations prior to use.
1.3 This international standard was developed in accor-
4.3 This test assumes that the rate of dissolution of the
dance with internationally recognized principles on standard-
chromium by the hydrochloric acid under the specified condi-
ization established in the Decision on Principles for the
tions is always the same.
Development of International Standards, Guides and Recom-
5. Test Solutions
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
5.1 For chromium on nickel the test solution is reagent
grade hydrochloric acid having a specific gravity at 16 °C of
2. Referenced Documents
1.180 6 0.002. (This corresponds to 11.5 N 6 0.2 N, which
may be checked by titration.) For chromium on stainless steel
2.1 ASTM Standards:
the test solution is 20 g/L of antimony trioxide dissolved in
B504 Test Method for Measurement of Thickness of Metal-
reagent grade hydrochloric acid having a specific gravity at
lic Coatings by the Coulometric Method
16 °C of 1.160.
B568 Test Method for Measurement of Coating Thickness
by X-Ray Spectrometry
NOTE 2—As received, reagent grade hydrochloric acid is normally
B588 Test Method for Measurement of Thickness of Trans-
more concentrated than 11.5 N.
parent or Opaque Coatings by Double-Beam Interference
6. Preparation of Test Area
6.1 The test area must be free of foreign material. Clean by
rubbing the test area with a paste of magnesium oxide, rinse it,
This guide is under the jurisdiction of ASTM Committee B08 on Metallic and
and dry it with a clean cloth or filter paper. Draw a ring with a
Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on Test
Methods.
diameter of about 6 mm on the test area with melted paraffin or
Current edition approved Nov. 1, 2023. Published November 2023. Originally
with a wax pencil.
approved in 1971. Last previous edition approved in 2018 as B556 – 90 (2018).
DOI: 10.1520/B0556-90R23.
7. Procedure
Blum, W., and Olson, W. A., Proceedings, Am. Electroplaters Soc., Vol 28,
1940, p. 25.
7.1 Let the test specimen, the test solution, and the dropper
DuRose, A. H., and Pierce, W. J., Metal Finishing , Vol 57, March 1959, p. 54.
stand long enough to reach room temperature, which should be
For referenced ASTM standards
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