If you look at gold jewelry purchased in India before the mid-2000s, you will likely see the letters "KDM" stamped on it. Today, you see "916" alongside a 6-digit alphanumeric code known as HUID. This transition represents one of the most important consumer protection evolutions in the Indian jewelry industry.
What was KDM Gold?
To make complex jewelry, pieces of gold must be soldered together. Solder must have a lower melting point than the gold itself, so the jewelry doesn't melt during the process. For decades, jewelers used Cadmium (abbreviated as KDM) mixed with gold to create this solder.
A "KDM" stamp meant that cadmium solder was used. Jewelers loved it because it flowed easily and didn't affect the final finish.
The Dark Side: Why KDM was Banned
There were two massive problems with KDM:
- Health Hazards: When melted, Cadmium releases highly toxic fumes. Artisans working in poorly ventilated workshops were developing severe respiratory illnesses and cancer. The BIS (Bureau of Indian Standards) eventually banned its use entirely to protect workers.
- Purity Dilution: Because Cadmium is not a precious metal, adding it to the solder diluted the overall purity of the piece. You might buy a 22K (91.6%) necklace, but due to the KDM solder, its actual melted purity might only be 89% or 90%. When customers went to resell, they were shocked by the purity deductions.
The Rise of 916 and Zinc Solder
After the ban, the industry shifted to using Zinc and Copper as soldering alloys. More importantly, the BIS enforced strict hallmarking. The term "916" became the gold standard. It simply means 91.6% pure gold (which equates to 22 Karats).
The Modern Era: What is HUID?
Even with 916 stamps, fraudulent jewelers were faking hallmarks. Enter HUID (Hallmark Unique Identification).
Introduced as a mandatory requirement, HUID is a 6-digit alphanumeric code laser-engraved on the jewelry. Every single piece of hallmarked jewelry has a unique code. You can download the official BIS Care App, type in the HUID, and instantly verify:
- The jeweler who manufactured it.
- The assaying center that tested it.
- The exact purity of the item.
What to Do with Old KDM Jewelry?
If you are looking to exchange old KDM jewelry, be prepared for a lower valuation. Jewelers will typically melt it and test it using an XRF (X-ray fluorescence) machine. Do not expect 91.6% purity; expect closer to 88-90%. To check today's equivalent value, use our Gold Value Calculator and adjust the purity percentage accordingly.