How to Acid Test Precious Metals (Using a Scratch & Touchstone Kit)
If you buy, sell, stack, or thrift precious metals, you’ve probably wondered:
“How do I know this is real?”
One of the most affordable and widely used methods for testing gold and silver at home is the acid scratch test, also called a touchstone test. While not perfect, it’s a practical tool that many dealers and collectors use to quickly verify metal purity.
Here’s how acid testing works — and how to use it safely and correctly.
What Is an Acid Test?
An acid test uses specially formulated testing acids to determine the purity of precious metals.
The process involves:
Lightly scratching the metal on a testing stone (touchstone)
Applying a small drop of acid
Observing how the metal reacts
Different acid strengths correspond to different purity levels.
What Comes in a Typical Testing Kit?
Most precious metal acid test kits include:
Black testing stone (touchstone)
Nitric acid (silver testing)
Gold testing acids (10k, 14k, 18k, 22k, sometimes platinum)
Small droppers
Reference chart
These kits are widely available online and at jewelry supply stores.
Safety First
Before testing:
Wear gloves
Use eye protection
Work in a well-ventilated area
Keep acids away from skin and surfaces
Neutralize spills with baking soda
Testing acids are corrosive and should be handled carefully.
How to Acid Test Gold
Step 1: Scratch the Item
Rub the item firmly against the testing stone to leave a visible metal streak.
Important:
Do NOT test plated areas.
Scratch in an inconspicuous area if testing jewelry.
Step 2: Apply the Correct Acid
Start with a lower karat acid (for example, 10k).
Observe the reaction:
No reaction: The metal is at least that karat or higher.
Streak fades or dissolves: The metal is below that karat.
Turns milky or green: Likely base metal or gold-plated.
Work upward with higher karat acids until you see a reaction.
How to Acid Test Silver
Silver is tested slightly differently.
Use nitric acid and observe:
Creamy white reaction: Likely sterling (.925)
Green reaction: Likely base metal
Cloudy gray: Possible lower silver purity
Be aware that silver-plated items will often show a misleading surface reaction if not scratched deeply enough.
What Acid Testing Can and Cannot Tell You
What It Can Do:
Quickly confirm gold or silver presence
Estimate approximate purity
Detect obvious fakes or plating
What It Cannot Do:
Guarantee exact fineness
Detect tungsten cores in gold bars
Replace professional XRF analysis
For high-value bullion or rare coins, professional testing is always recommended.
When Should You Use an Acid Test?
Acid testing is useful when:
Buying scrap jewelry
Evaluating thrift store finds
Testing estate sale silver
Confirming unknown items
It is not recommended for:
High-value collectible coins
Graded slabs
Proof or numismatic pieces
Scratching collectible coins will permanently damage them.
Alternatives to Acid Testing
If you want more accuracy without scratching:
Magnet test (precious metals are non-magnetic)
Weight and measurement test
Specific gravity test
XRF testing (professional method)
Many serious stackers use acid testing as a first step, then confirm with additional methods for large purchases.
Final Thoughts
Acid testing is one of the most accessible tools for precious metal verification. It’s inexpensive, portable, and effective when used correctly — but it should be part of a broader verification strategy, not the only test you rely on.
Whether you're stacking silver, flipping gold jewelry, or evaluating estate finds, knowing how to properly acid test can protect you from costly mistakes.
To calculate melt value, track purity, and log precious metal finds, visit CoinCollectingTools.com.