To explore new/alternative assaying methods to the fire assay method for testing of gold jewellery and artefacts through non-destructive testing
Organization: Ministry of Consumer Affairs Food & Public Distribution (MoCA F&PD)
Category: Hardware | Theme: Miscellaneous

Background:
Hallmarking is the accurate determination and official recording of the proportionate content of precious metal in the jewellery/artefacts or bullion/coins. The hallmarking of gold jewellery was started in year 2000 and has been made mandatory since 23 June 2021 and presently covers 361 districts.

The Indian Standard, IS 1417 2016 "Gold and gold alloys, jewellery/artefacts-fineness and marking specification" covers hallmarking of six grades of gold jewellery/gold artefacts viz. 14K, 18K, 20K, 22K, 23K and 24K carats. The Indian Standard, IS 1418: 2009 "Determination of gold in gold bullion, gold alloys and gold jewellery/artefacts - Cupellation (Fire Assay) method" prescribes the fire assay test method for determining the fineness of gold in gold bullion, alloys, and jewellery/artefacts.

The fire assay testing method, though globally accepted and accurate, involves a destructive testing process wherein a sample of 250-500 mg is taken from the item by scrapping, drilling, or cutting. The method may lead to the damage of the article, rendering it unsellable, especially when dealing with a few or single article. However, the gold loss incurred during testing is almost negligible. Additionally, the process emits hazardous substances like lead oxides and nitrous fumes.

Further, BIS has also formulated an Indian Standard on method of test using ED-XRF (Energy Dispersive X-Ray Fluorescence), i.e., IS 18458: 2023 "Jewellery and precious metals ED-XRF test - Method of test". This Indian Standard prescribes a non-destructive testing method to verify the fineness of the gold jewellery. However, the use of ED-XRF as a non-destructive method to determine the fineness is only applicable to homogenous gold jewellery. In addition, IS 18458: 2023 also has a provision for determination of fineness of jewellery by destructive testing, which is more suited for non-homogeneous jewellery.

There is another Indian Standard developed by BIS, IS 16901: 2022 "Jewellery and precious metals determination of high purity gold, platinum and palladium - difference method using ICP-OES". This method uses ICP-OES and is applicable only for high purity gold (999 ppt and above). ICP-OES is also a destructive testing method.

India's gold jewellery industry is highly diverse, encompassing various types such as casted jewellery, handmade pieces with soldered joints, hollow and filled jewellery, gold-plated items, and studded ornaments using various jewellery manufacturing techniques. While casted jewellery is relatively homogeneous, the majority-particularly handmade and hollow varieties-are structurally complex and heterogeneous. This variability presents significant challenges in testing and hallmarking.

In the existing fire assay testing method, heterogeneity is addressed by melting the sample before testing. This eliminates impurities and ensures homogeneity. Moreover, fire assay being a difference method (based on initial and final weight of gold sample), the impact of heterogeneity is nullified. However, owing to its destructive nature, there is strong demand for an alternative non-destructive testing method.

Expected Solution:
a. Develop and implement a non-destructive assaying method that matches the accuracy of fire assay without damaging the jewellery, while being capable of handling heterogeneous compositions (solders, fillers, non-metallic substances).
b. Eliminate emissions of harmful substances (lead oxide, nitrous fumes).
c. Achieve repeatability close to that of fire assay, ideally within ±0.5 ppt (as per IS 1418).
d. Method selected will be validated for regulatory and commercial applications.

Deliverables:
a. Detailed non-destructive innovative testing method with technical explanation
b. References/bibliography related to the technical paper
c. Scientific principles underlying the approach
d. Feasibility studies and expected challenges
e. Methodology for validation including accuracy assessment
f. Explanatory note on potential for regulatory and commercial application