The measurement of the gold content of gold coins and jewellery through the ages has been an essential requirement to protect the buyer from fraud and the seller from loss of profit. That requirement remains important for both the seller (the jewellery manufacturer) and the buyer (the consumer) in today's tightly legislated society. The ancient techniques of gold assay - touchstone, density and fire assay - are still in use today. These have been complemented by new instrumental techniques in the latter half of the 20th century - including ICP and AA spectrometry and X-ray fluorescence - and progress in their capabilities continues to be made. This review of gold assaying techniques examines each in terms of its suitability for jewellery use. The main characteristics of each technique - including cost, speed, sampling, accuracy and limitations - are reviewed, and their suitability for in-house quality control and hallmarking are discussed. Surprisingly, fire assay remains the reference technique against which all others are compared. XRF continues to make progress and is seeing ever-wider application; some thoughts on new, cost-effective assaying techniques are also considered.

Author: Dr. Christopher W. Corti