Understand the touchstone method used for comparative karat-gold testing. This guide explains what you are comparing, what reactions can indicate, why sampling location matters, and why corrosive test chemicals require careful handling.
Interpret the observed comparison without overclaiming certainty.
A plated item can contain a gold-rich surface over base metal. Testing only the outer surface can therefore produce a misleading result. GIA's touchstone guidance emphasizes examining the piece and, where appropriate, exposing representative fresh metal in an inconspicuous location. 2
Touchstone testing works by comparing the behavior of an unknown streak against known samples. It is useful because different gold purities have different resistance to suitable testing solutions, but technique and sampling quality matter.
Gold acid testing involves corrosive substances. Use proper protective equipment, ventilation, compatible containers and the testing kit manufacturer's instructions. Do not mix concentrated acids from improvised recipes, and keep chemical waste out of ordinary household drains.
For high-value jewellery, disputes, large purchases or items suspected of complex construction, use additional evidence such as specific gravity, density, XRF or professional assay. No single home screening method should be treated as absolute proof.
It compares an unknown gold sample with known karat reference samples under controlled testing conditions.
It provides a comparative estimate rather than laboratory-grade compositional analysis.
Only with appropriate chemical safety procedures and the correct testing equipment.
No. Surface testing can be misleading on layered items.
A comparatively nondestructive method using reference gold samples on a testing stone.