ISO 13756:2024

Overview

ISO 13756:2024 is an international standard published by the International Organization for Standardization (ISO) that specifies a volumetric potentiometric method for the determination of silver content in jewellery and precious metals. The method uses sodium chloride (NaCl) or potassium chloride (KCl) as titrants and is applied to homogeneous materials with a silver content preferably ranging between 100 and 999 parts per thousand (‰) by mass. For fineness values above 999 ‰, alternative methods such as spectroscopy by difference (e.g., ISO 15096) are recommended.

This third edition supersedes the 2015 version and expands the applicability of the method to a wider range of silver alloys. It serves as the reference method for determining silver fineness in alloys covered under ISO 9202.

Key Topics

• Scope and Application
  The method targets the accurate determination of silver content in precious metal alloys used in jewellery and related fields. It is intended for materials considered homogeneous with a silver content up to 999 ‰.

• Principle of Measurement
  The sample is dissolved in dilute nitric acid. Silver concentration is then quantified by titration with a sodium chloride or potassium chloride solution. The equivalence point is detected potentiometrically, with elimination of palladium interferences if needed.

• Reagents and Equipment

  • Use of analytical grade reagents such as 33% nitric acid and 0.1 mol/L sodium or potassium chloride solutions.
  • Equipment includes precision burettes or motorized titrators, potentiometric electrodes (silver or silver chloride electrodes and Hg/HgSO4 reference electrodes), and analytical balances with 0.01 mg precision.

• Procedure Highlights

  • Preparation of standard silver solutions for calibration.
  • Elimination of palladium if present, using dimethylglyoxime reagent to avoid measurement interference.
  • Precise potentiometric titration to obtain the equivalence point with 0.05 mL volume increments.

• Calculation and Reporting
  Calculations translate titration volume and calibration factors into silver mass and fineness values expressed in parts per thousand. The method ensures high repeatability, with acceptable result differences below 1 ‰.

• Safety and Sampling
  Emphasis on strict adherence to laboratory safety and hygiene practices. Sampling procedures must comply with ISO 11596 to ensure representativeness and reliability.

Applications

• Jewellery Industry
  Reliable quantification of silver content is critical for quality assurance, valuation, hallmarking, and regulatory compliance in jewellery fabrication and trade.

• Precious Metals Assaying
  Laboratories performing precious metal assays trust the standardized potentiometric method to provide consistent, traceable results, especially for silver-containing alloys with moderate fineness.

• Material Certification and Control
  The method supports manufacturers and certification bodies in validating alloy compositions as per international standards, enhancing consumer confidence and market transparency.

• Research and Development
  Metallurgists and quality control analysts utilize this method during formulation and testing of new silver-based alloys for technical or aesthetic purposes.

Related Standards

• ISO 9202 – Jewellery, precious metals – Marking of precious metal alloys – It defines alloy categories and acceptable fineness ranges for precious metals, aligning with the scope of ISO 13756.

• ISO 11596 – Jewellery, precious metals – Sampling of precious metal and precious metal alloys – Provides guidelines for obtaining representative samples, crucial for accurate silver determination.

• ISO 15096 – Jewellery, precious metals – Determination of high-purity silver content by difference spectroscopy – Recommended for silver fineness above 999 ‰, complementing the potentiometric method.

By adhering to ISO 13756:2024, laboratories and industry professionals benefit from a rigorously defined, validated reference procedure for accurate silver content measurement in precious metal alloys, fostering standardization and confidence in precious metals quality assessment worldwide.