ASTM D2448-85(2019)

Standard Test Method for Water-Soluble Salts in Pigments by Measuring the Specific Resistance of the Leachate of the Pigment

SIGNIFICANCE AND USE
4.1 This test method provides a reliable means for the determination of the relative amounts of these salts when comparing different lots of the same pigment grade. Water-soluble salts also affect the water resistance and blister resistance of coatings, especially primers for steel. Conductivity measurements, however, cannot be used as the only method to determine and compare the amount of water soluble salts of pigments with the same chemical composition but produced by different manufacturing processes.
SCOPE
1.1 This test method covers the determination of the specific resistance of the aqueous leachate from a pigment as an index of water-soluble salt content. This test method is applicable to white pigments and colored pigments (organic and inorganic). The water-soluble salts content is a function of the specific resistance of the solution formed by extracting the pigment with water.  
1.2 This test method is based on a water to pigment ratio of 9+1. The leachate yield (minimum 160 mL) sufficient for rinsing the cylinder dip cell and thermometer plus the minimum 80 mL required for the measurement to determine the quantity of pigment to be used.  
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.4 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.  
1.5 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-Sep-2019
• ICS: 87.060.10 - Pigments and extenders
• Technical Committee: D01 - Paint and Related Coatings, Materials, and Applications
• Drafting Committee: D01.31 - Pigment Specifications

Relations

• Replaces: ASTM D2448-85(2012) - Standard Test Method for Water-Soluble Salts in Pigments by Measuring the Specific Resistance of the Leachate of the Pigment
• Effective Date: 01-Oct-2019
• Refers: ASTM D1193-06 - Standard Specification for Reagent Water
• Effective Date: 01-Mar-2006
• Refers: ASTM D1193-99e1 - Standard Specification for Reagent Water
• Effective Date: 10-Feb-1999
• Refers: ASTM D1193-99 - Standard Specification for Reagent Water
• Effective Date: 10-Feb-1999
• Referred By: ASTM D717-86(2020) - Standard Test Methods for Analysis of Magnesium Silicate Pigment
• Effective Date: 01-Oct-2019
• Referred By: ASTM D476-15(2021) - Standard Classification for Dry Pigmentary Titanium Dioxide Products
• Effective Date: 01-Oct-2019
• Referred By: ASTM D1135-86(2020) - Standard Test Methods for Chemical Analysis of Blue Pigments
• Effective Date: 01-Oct-2019
• Referred By: ASTM D6280-98(2020) - Standard Specification for Zinc Phosphate Pigments
• Effective Date: 01-Oct-2019
• Referred By: ASTM D718-86(2020) - Standard Test Methods for Analysis of Aluminum Silicate Pigment
• Effective Date: 01-Oct-2019

Overview

ASTM D2448-85(2019) - Standard Test Method for Water-Soluble Salts in Pigments by Measuring the Specific Resistance of the Leachate of the Pigment provides a standardized procedure for assessing the water-soluble salt content in both white and colored (organic or inorganic) pigments. This method determines the specific resistance of the aqueous leachate resulting from extracting pigment with water, offering a reliable index of salt levels within pigment batches. The assessment of water-soluble salts is essential, as these impurities significantly impact the water resistance and blister resistance of coatings, particularly primers applied to steel substrates.

This standard is widely applied within pigment manufacturing, quality control of coatings, and materials testing laboratories, ensuring batch-to-batch consistency and the reliable performance of finished products.

Key Topics

• Test Scope: Applicable to both white and colored pigments, including organic and inorganic varieties.
• Measurement Principle: Relies on measuring the specific resistance (or electrical resistivity) of a pigment’s aqueous leachate, with the resistance inverse to the water-soluble salt content.
• Sample Preparation: Utilizes a water-to-pigment ratio of 9:1 to extract soluble salts; method adjustments accommodate both hydrophilic and hydrophobic pigments.
• Instrumentation:
  • Conductivity bridge and cell with appropriate constants for specific resistance range
  • Thermometer with fine resolution (0.2°C increments)
  • Centrifuge and high-grade filter paper to remove pigment solids
  • Reagent-grade water and chemicals, such as potassium chloride for calibration
• Temperature Control: Measurements are standardized at 25°C for accurate and reproducible results.
• Repeatability & Reproducibility: Precision is specified for both intra-laboratory (repeatability) and inter-laboratory (reproducibility) testing, helping ensure consistent outcomes.

Applications

• Quality Assurance in Pigment Production: Enables manufacturers to detect batch variation and maintain consistent pigment quality by monitoring water-soluble salt content.
• Coatings and Paints Industry: Critical for evaluating pigment batches intended for primers and protective layers, where water resistance and blister resistance are key performance indicators.
• Raw Material Selection: Assists procurement and R&D teams in comparing lots of pigments, especially when switching suppliers or manufacturing processes.
• Comparative Testing: Useful for benchmarking different pigment grades and verifying that they meet specified criteria for water-soluble salt levels.
• Regulatory Compliance & Specification Development: Supports compliance with international trade and product safety guidelines, conforming to WTO’s standardization principles.

Related Standards

• ASTM D1193 - Specification for Reagent Water: Referenced for water quality requirements within this test method.
• Other ASTM Pigment and Coating Standards: Commonly used in conjunction for comprehensive quality control and performance testing.
• International Standards:
  • WTO TBT Committee principles for standard development
  • Relevant ISO standards on pigment testing and paint raw materials

Practical Value

ASTM D2448-85(2019) ensures reliability in pigment quality control by enabling robust, repeatable measurement of water-soluble salts. By following this standard, manufacturers, formulators, and laboratories can:

• Detect and address variations in pigment production
• Prevent performance issues in coatings related to excessive water-soluble salts
• Improve product lifespan, particularly for coatings exposed to moisture or harsh environments
• Facilitate international trade by adhering to globally recognized testing protocols

Keywords: ASTM D2448, specific resistance, water-soluble salts, pigment testing, leachate, coatings industry, paint additives, pigment quality, conductivity measurements, ISO pigment standards, quality control.

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: D2448 −85 (Reapproved 2019)
Standard Test Method for
Water-Soluble Salts in Pigments by Measuring the Specific
Resistance of the Leachate of the Pigment
This standard is issued under the fixed designation D2448; 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 3. Summary of Test Method
1.1 Thistestmethodcoversthedeterminationofthespecific
3.1 A weighed quantity of pigment is added to water and
resistance of the aqueous leachate from a pigment as an index
boiled. For hydrophobic pigments methyl alcohol is used to
of water-soluble salt content. This test method is applicable to
facilitate wetting. After filtration, the specific resistance of the
white pigments and colored pigments (organic and inorganic).
filtrate is determined using a conductivity bridge.
The water-soluble salts content is a function of the specific
resistance of the solution formed by extracting the pigment
4. Significance and Use
with water.
4.1 This test method provides a reliable means for the
1.2 This test method is based on a water to pigment ratio of
determination of the relative amounts of these salts when
9+1. The leachate yield (minimum 160 mL) sufficient for
comparing different lots of the same pigment grade. Water-
rinsing the cylinder dip cell and thermometer plus the mini-
soluble salts also affect the water resistance and blister resis-
mum 80 mL required for the measurement to determine the
tance of coatings, especially primers for steel. Conductivity
quantity of pigment to be used.
measurements, however, cannot be used as the only method to
determine and compare the amount of water soluble salts of
1.3 The values stated in SI units are to be regarded as
pigments with the same chemical composition but produced by
standard. No other units of measurement are included in this
different manufacturing processes.
standard.
1.4 This standard does not purport to address all of the
5. Apparatus
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
5.1 Centrifuge (optional), having a 500-mL capacity per
priate safety, health, and environmental practices and deter-
cup.
mine the applicability of regulatory limitations prior to use.
5.2 Filter Paper (Note 1)—For high reliability avoid use of
1.5 This international standard was developed in accor-
filter paper containing soluble material. Each filter should be
dance with internationally recognized principles on standard-
washed with reagent water in the funnel until resistance of the
ization established in the Decision on Principles for the
filtrate is greater than 200 000Ω · cm.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical NOTE 1—The size of the filter paper will be determined by how
voluminous the pigment is. Some organic pigments require at least a
Barriers to Trade (TBT) Committee.
185-mm paper for proper filtering.
2. Referenced Documents
5.3 Filter Aid (optional)—The use of a filter aid may be
desirable with some pigments to improve filtration. However,
2.1 ASTM Standards:
the filter aid must be treated to meet the same specifications for
D1193 Specification for Reagent Water
filter paper as given in 5.2.
5.4 Ungraduated Cylinders, approximately 35 mm wide by
This test method is under the jurisdiction of ASTM Committee D01 on Paint 125 mm deep.
and Related Coatings, Materials, andApplications and is the direct responsibility of
5.5 Thermometer, graduated in 0.2°C intervals.
Subcommittee D01.31 on Pigment Specifications.
Current edition approved Oct. 1, 2019. Published October 2019. Originally
5.6 Conductivity Bridge.
approved in 1966. Last previous edition approved in 2012 as D2448 – 85 (2012).
DOI: 10.1520/D2448-85R19.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Any commercially produced conductivity bridge and conductivity cell is
the ASTM website. satisfactory.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2448 − 85 (2019)
5.7 Conductivity Cell, having a cell constant, K,of1.The 6.4 Potassium Chloride, Standard Solution (0.02 N)—
cell constant recommended for various ranges of electrolytes is Prepare a 0.02 N potassium chloride (KCl) solution with water
as follows: by dissolving 1.491 g of KCl (heated before weighing for 1 h
5.7.1 For specific resistances of less than 250Ω · cm, use a at 105°C) in water, followed by dilution to 1 L.
cell with a constant of 10 or more.
7. Determination of Cell Constant
5.7.2 For specific resistances from 250 to 200 000Ω · cm,
7.1 Prepare a 0.002 N solution of KCl by diluting the 0.02
use a cell with a constant of 1. This covers the range for most
N KCl solution described in 6.4 with water. Cool and measure
pigments.
the specific resistance, R ,at25 60.5°C as described in 8.2.2.
5.7.3 For specific resistances of reagent water or of over m
200 000Ω · cm, use a cell with a constant of 0.1.
7.2 Calculate the cell constant, K, as follows:
K 5 R /R
~ !
25 m s
6. Reagents
where:
6.1 Purity of Reagents—Reagent grade chemicals shall be
R = specific resistance at 25°C (see 8.2.2), and
used in all tests. Unless otherwise indicated, it is intended that
m
R = specific resistance in ohm centimetres of an 0.002 N
all reagents shall conform to the specifications of the Commit-
s
KCl solution at 25°C (Table 1) = 3427Ω · cm.
tee onAnalytical Reagents of theAmerican Chemical Society,
where such specifications are available. Other grades may be
NOTE 2—In general the “cell constant” is not greatly affected by
used, provided it is first ascertained that the reagent is of variations in the strength of the KCl solution, but for
...