Gold Lab: How to Check Gold Purity With Your Phone

Gold is one of the most traded commodities in the world — and also one of the most commonly misrepresented. Whether you're buying jewelry at a bazaar, inheriting a family heirloom, or selling old gold, knowing the actual purity of what you're holding is critical. Gold Lab puts that knowledge directly in your pocket.

What Is Gold Karat — and Why Does It Matter?

Gold karat (often written as 'K' or 'kt') is a measure of gold purity expressed as a fraction of 24 parts. Pure gold is 24K. Most jewelry is not pure gold — it's alloyed with other metals like silver, copper, or zinc to increase durability, since pure gold is too soft for everyday wear.

24K — 99.9% pure gold. The most valuable, but too soft for most jewelry. Used for investment bars and coins.
22K — 91.7% gold. Common in South Asian and Middle Eastern jewelry. Very high value.
18K — 75% gold. The most popular choice for fine jewelry worldwide. Excellent balance of purity and durability.
14K — 58.3% gold. Very popular in Western markets. Durable and more affordable.
10K — 41.7% gold. The minimum karat that can legally be sold as gold in many countries.
9K — 37.5% gold. Common in the UK and Australia for budget jewelry.

The higher the karat, the more valuable the piece — but also the softer and more susceptible to scratching. Understanding karat is essential when buying, selling, or appraising gold.

How Gold Lab Works

Gold Lab uses your Android device's built-in electromagnetic sensors — specifically the magnetometer (the same sensor used for your phone's compass) — to analyze the electromagnetic properties of a material. Since different gold alloys have distinct electromagnetic signatures depending on their composition, the app's algorithms can estimate the purity level of the gold you're testing.

Good to Know

Gold Lab is an estimation tool. It provides a strong indication of gold purity — especially useful for quick checks before a purchase or appraisal. For legally binding valuations, always use a certified assay office.

The entire process is on-device. No data is sent to a server, no internet connection is needed, and nothing is stored. Your assessment is completely private.

Step-by-Step: Using Gold Lab

1Open Gold Lab and wait for the sensor to calibrate. The app will show a readiness indicator when it's ready. This takes 3–5 seconds.
2Place your phone on a flat, stable surface. Movement during the reading introduces inaccuracy, so avoid holding the phone in your hand.
3Position your gold item directly against the back of the phone, centered over the camera module area where the magnetometer sensor is typically located.
4Keep the item completely still and tap 'Start Reading'. The app will take a 10–15 second measurement.
5Read your result. Gold Lab will display an estimated karat range (e.g. '18K–20K') along with a confidence indicator.
6For best accuracy, take 3 readings and average the results. Remove and reposition the item between each reading.

Tips for Getting the Most Accurate Readings

Accuracy depends heavily on how you use the app. Follow these best practices and you'll consistently get reliable estimates.

Calibrate on an empty surface first — place your phone flat with nothing nearby, then open the app and let it zero the sensor before bringing in your gold item.
Keep your phone away from other metal objects during the reading. Other metals — keys, coins, rings, a metal desk — interfere with the electromagnetic field.
Remove your phone case if it has a metal plate or magnetic component (like a car mount attachment), as these will skew the reading.
Test on the main body of the piece, not the clasp or setting. Clasps are often made from different, lower-karat alloys.
Avoid testing near electronic devices, speakers, or appliances. Their electromagnetic fields create noise in the reading.
Take multiple readings on different parts of the item and average them for better reliability.

Pro Tip

If you get inconsistent readings between attempts, the item likely contains multiple metals or has a non-uniform alloy composition — common in older jewelry or pieces with decorative inlays. This is useful information in itself.

Understanding Your Results

Gold Lab gives you a karat estimate, not a single fixed number. Here's how to interpret what you see:

If the reading is close to 24K — the item is likely very high purity gold or gold-plated with thick plating.
If the reading falls in the 18K–22K range — consistent with standard fine jewelry in South Asian, Middle Eastern, or European markets.
If the reading is around 14K–18K — typical of Western fine jewelry.
If the reading falls below 10K — the item may be gold-filled, gold-plated over a base metal, or not gold at all.
A very inconsistent or low reading on an item sold as gold is a red flag worth investigating further.

“Always cross-check a result that surprises you. Request a hallmark certificate from the seller, look for stamped karat marks on the piece (usually inside a ring band or on a clasp), and when in doubt, consult a professional jeweler.”

What Gold Lab Cannot Do

Being honest about limitations helps you use the tool most effectively.

It cannot provide a legally valid valuation or certificate of purity — only a certified assay lab can do that.
It may struggle with very thin gold plating, as the base metal's signal dominates the reading.
It cannot distinguish between two different alloys with similar electromagnetic properties but different compositions.
Results may vary slightly across different phone models because the magnetometer placement and sensitivity differ between manufacturers.

Real-World Use Cases

Buying jewelry at a market or bazaar — get a quick sanity check before negotiating a price.
Inheriting old jewelry — understand what you've received before taking it to an appraiser.
Selling old gold — know roughly what your pieces are worth before walking into a gold buyer's shop.
Teaching — gold Lab is an excellent educational tool for understanding material science and electromagnetic properties.
Curiosity — sometimes you just want to know what that old ring in the drawer is actually made of.

Final Thoughts

Gold Lab won't replace a professional assay, but it gives you something invaluable: informed confidence. Knowing what you're dealing with before a transaction — whether buying or selling — puts you in a far stronger position. The app is completely free, requires no account, works offline, and collects no data. It's the kind of tool that quietly earns its place on your home screen.