ASTM D6657-16(2021)

Standard Test Method for pH of Wet Blue and Wet White

SIGNIFICANCE AND USE
4.1 This test method is designed to measure the pH of a distilled-water extract of Wet Blue and Wet White. This is considered to be a measure of the acidity or alkalinity of the Wet Blue or Wet White. Excessive acidity or alkalinity may have a deleterious effect on the aging characteristics of Wet Blue and Wet White and the leather made from it.  
4.2 This test method is suitable for development, control, and service evaluation of wet blue.
SCOPE
1.1 This test method covers the determination of the pH of all types of Wet Blue and Wet White.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.3 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.  
1.4 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-Aug-2021
• ICS: 59.140.10 - Processes and auxiliary materials
• Technical Committee: D31 - Leather
• Drafting Committee: D31.02 - Wet Blue

Relations

• Refers: ASTM D6659-10(2015) - Standard Practice for Sampling and Preparation of Wet Blue for Physical and Chemical Tests
• Effective Date: 01-Dec-2015
• Refers: ASTM E177-14 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2014
• Refers: ASTM E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM E177-13 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2013
• Refers: ASTM E691-11 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2011
• Refers: ASTM D6659-10 - Standard Practice for Sampling and Preparation of Wet Blue for Physical and Chemical Tests
• Effective Date: 01-Oct-2010
• Refers: ASTM E177-10 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Oct-2010
• Refers: ASTM E177-08 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Oct-2008
• Refers: ASTM E691-08 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Oct-2008
• Refers: ASTM D6659-08 - Standard Practice for Sampling and Preparation of Wet Blue for Physical and Chemical Tests
• Effective Date: 01-Sep-2008
• Refers: ASTM D6659-01(2007) - Standard Practice for Sampling and Preparation of Wet Blue for Physical and Chemical Tests
• Effective Date: 01-Sep-2007
• Refers: ASTM E177-06b - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 15-Nov-2006
• Refers: ASTM E177-06a - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Nov-2006
• Refers: ASTM E691-05 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2005
• Refers: ASTM E177-04 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Nov-2004

Overview

ASTM D6657-16(2021) is the globally recognized standard test method for determining the pH of Wet Blue and Wet White leather. Developed by ASTM International, this standard assesses the acidity or alkalinity of a distilled-water extract from all types of Wet Blue (chrome-tanned) and Wet White (alternative pre-tanned) leathers. The pH of these substrates is an important quality parameter, as excessive acidity or alkalinity can compromise the aging characteristics of the leather and impact its service life and performance in subsequent manufacturing processes.

This method is applicable for development, quality control, and service evaluation within the leather industry, providing a consistent, reproducible framework for pH measurement.

Key Topics

• Scope and Applicability: Covers all types of Wet Blue and Wet White stock, standardizing pH assessment using only SI units.
• Significance of pH Measurement: Evaluates potential effects of acidity or alkalinity on leather durability, stability, and further processing.
• Testing Protocol: Involves extracting the pH with distilled water and measuring with a calibrated electronic pH meter to an accuracy of 0.01 pH units.
• Sampling and Preparation: Requires representative composite samples following ASTM D6659 for accurate results.
• Precision and Repeatability: Real-world precision and repeatability are established through multi-laboratory studies, ensuring the method's reliability and industry acceptance.

Applications

ASTM D6657-16(2021) is essential for:

• Leather Manufacturers: Ensuring finished Wet Blue and Wet White stocks meet internal and customer specifications regarding chemical stability and aging properties.
• Quality Assurance Labs: Performing regular process control and service evaluation, monitoring pH changes that may affect the final product after tanning.
• Product Development: Supporting R&D by providing consistent data on how processing methods or chemical formulations affect the pH and resulting properties of semi-processed leathers.
• Compliance and Trade: Meeting international trade requirements for technical quality and regulatory expectations, as this standard aligns with WTO TBT Committee principles.
• Customer Assurance: Providing end-users and downstream manufacturers with verifiable quality parameters for intermediate leather goods.

Related Standards

• ASTM D6659: Practice for sampling and preparation of Wet Blue and Wet White for physical and chemical tests.
• ASTM E177: Practice for use of the terms precision and bias in ASTM test methods, supporting data analysis and interpretation.
• ASTM E691: Practice for conducting interlaboratory studies to determine the precision of a test method, underlying the robust precision statement of this pH test.
• ISO and Regional Leather Standards: While ASTM D6657 is widely used, harmonization with relevant ISO standards can facilitate international trade and mutual recognition.

Practical Value

Implementing ASTM D6657-16(2021) in laboratory and production environments helps ensure leather quality, prevent product failures due to improper pH levels, and minimize costly recalls or reprocessing. Regular use of this test method fosters confidence in the chemical integrity of Wet Blue and Wet White, underpinning product longevity and brand reputation in the global leather industry.

Keywords: ASTM D6657, Wet Blue, Wet White, leather pH, acidity, alkalinity, chemical testing, quality control, leather industry standards, aging characteristics, WTO TBT compliance.

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: D6657 − 16 (Reapproved 2021)
Standard Test Method for
pH of Wet Blue and Wet White
This standard is issued under the fixed designation D6657; 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 4. Significance and Use
1.1 This test method covers the determination of the pH of 4.1 This test method is designed to measure the pH of a
all types of Wet Blue and Wet White. distilled-water extract of Wet Blue and Wet White. This is
considered to be a measure of the acidity or alkalinity of the
1.2 The values stated in SI units are to be regarded as
Wet Blue or Wet White. Excessive acidity or alkalinity may
standard. No other units of measurement are included in this
have a deleterious effect on the aging characteristics of Wet
standard.
Blue and Wet White and the leather made from it.
1.3 This standard does not purport to address all of the
4.2 This test method is suitable for development, control,
safety concerns, if any, associated with its use. It is the
and service evaluation of wet blue.
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
5. Apparatus
mine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accor-
5.1 Electronic pH Meter, with a suitable electrode. The
dance with internationally recognized principles on standard-
meter shall have an accuracy of at least 0.01 pH unit and
ization established in the Decision on Principles for the
reproducibility of 0.05 pH unit.
Development of International Standards, Guides and Recom-
5.2 Analytical Balance, sensitive to 0.01 g or greater.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
6. Reagents
6.1 Purity of Water—Unless otherwise indicated, references
2. Referenced Documents
to water shall be understood to mean distilled water or water of
2.1 ASTM Standards:
equal purity. Distilled water shall have a pH value of not less
D6659 Practice for Sampling and Preparation of Wet Blue
than 5.5 nor more than 7.0 and shall give a residue of not more
and Wet White for Physical and Chemical Tests
than 0.5 mg, when 100 mL is evaporated and dried in a
E177 Practice for Use of the Terms Precision and Bias in
platinum dish.
ASTM Test Methods
6.2 Commercially Standardized pH Solutions :
E691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method 6.2.1 Alkaline Phosphate Buffer Solution (0.01 M trisodium
phosphate, pH = 11.72 at 25 °C)—Dissolve 1.42 g of anhy-
3. Terminology drous disodium hydrogen phosphate (Na HPO ) in 100 mL of
2 4
a 0.1 N carbonate-free solution of sodium hydroxide (NaOH)
3.1 Definitions of Term Specific to this Standard:
and dilute to 1 L with water.
3.1.1 The pH of a solution has been defined as the negative
6.2.2 Borax Buffer Solution (0.01 M, pH = 9.18 at 25
logarithm of the hydrogen ion activity. A solution of pH 7 is
°C)—Dissolve 3.81 g of sodium tetraborate decahydrate
neutral at 24 °C. Lower numbers indicate increasing acidity;
(Na B O · 10H O) in water and dilute to 1 L.
2 4 7 2
higher numbers, increasing alkalinity.
6.2.3 Hydrochloric Acid (pH = 1.10 at 25 °C)—Add2gof
concentrated hydrochloric acid (HCl, sp gr 1.19) to 450 g of
water. Standardize and dilute to 0.1 N.
This test method is under the jurisdiction ofASTM Committee D31 on Leather
6.2.4 Phosphate Buffer Solution (0.025 M with respect to
and is the direct responsibility of Subcommittee D31.02 on Wet Blue.
each phosphate, salt pH = 6.86 at 2.5 °C)—Dissolve 3.40 g of
Current edition approved Sept. 1, 2021. Published October 2021. Originally
approved in 2001. Last previous edition approved in 2016 as D6657 - 16. DOI:
10.1520/D6657-16R21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Commercial buffer salts and solutions prepared in accordance with National
Standards volume information, refer to the standard’s Document Summary page on Bureau of Standards recommendations are sold by reputable laboratory supply
the ASTM website. houses and may be used.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6657 − 16 (2021)
monobasic potassium phosphate (KH PO ) and 3.55 g of precision and bias statements was mandated. The pH of Wet
2 4
anhydrous dibasic sodium phosphate (Na HPO ) in water and Blue can change significantly over time after removal from the
2 4
dilute to 1 L. chrome-tanning vessel. This change happens because chemical
6.2.5 Potassium Hydrogen Phthalate Buffer Solution (0.05 reactions involving the basicity of the chromium sulfate
M, pH = 4.01 at 25 °C)—Dissolve 10.21 g of potassium complex continue to occur within the Wet Blue. The amount
hydrogen phthalate (KHC H O ) in water and dilute to 1 L. and rate of these pH changes is dependent on the specific
8 4 4
processes and materials used to manufacture theWet Blue.The
7. Test Specimen
user is cautioned to verify that the precision and bias (or
reproducibility) of this method is adequate for the contem-
7.1 The specimen shall consist of a composite sample
plated application.
prepared according to Practice D6659.
7.1.1 Practice D6659—Sample Preparation Method A (as
11.2 A real world precision statement was determined
received in wet state, diced): use 10 61g.
through statistical examination of 145 results from 9
7.1.2 Practice D6659—Sample Preparation Method B
laboratories,on16materialsovernearly2years.PracticeE691
(oven or air dried, ground): use2-5g.
was followed for the design and analysis of the data.The terms
below (repeatability and reproducibility) are used as specified
8. Standardization
in Practice E177.
8.1 Use manufacturer’s directions for establishing two point
11.2.1 Repeatability (r)—The difference between repetitive
standardization with standard pH solutions that read on either
results obtained by the same operator in a given laboratory
side of the anticipated pH of the solution to be tested. Wash
applying the same test method with the same apparatus under
electrodes by immersing in three changes of water and estab-
constant operating conditions on identical test material within
lish a fresh liquid junction after blotting electrodes if using
short intervals of time would in the long run, in the normal and
sleeve type electrode prior to testing each solution.
correct operation of the test method, exceed the following
values only in one case in 20.
8.2 Check for electrode drift with either of the buffers and
11.2.2 Reproducibility (R)—the difference between two
restandardize if necessary.
single and independent results obtained by different operators
9. Procedure applying the same test method in different laboratories using
differen
...