How to Test Gold with Nitric Acid: Step-by-Step Safety & Accuracy Guide
I see a lot of questions here about verifying gold purity, especially for higher-karat pieces where electronic testers can be unreliable. Here's a complete walkthrough of acid testing that covers safety, procedure, and how to read results accurately.
What You'll Need
- Nitric acid solutions for 10K, 14K, 18K, and 22K
- Black testing stone (basalt scratch stone)
- Nitrile gloves and safety glasses
- Well-ventilated area (outdoors or near open window)
- Baking soda and water for neutralizing spills
- Paper towels
Safety First
⚠️ Nitric acid is corrosive and releases fumes. Always follow these rules:
- Wear gloves and eye protection—no exceptions
- Work in ventilated space, never in a closed room
- Keep baking soda paste (1:1 with water) ready for spills
- Store bottles upright, away from kids and pets
- Never mix acid bottles or share droppers
Step-by-Step Testing
Step 1: Prepare workspace
Lay down paper towels, set stone on flat surface, put on gloves and glasses.
Step 2: Make a streak
Rub the jewelry on an inconspicuous spot (inside ring band, back of pendant) firmly across the stone 3-4 times. Leave a visible 1-inch gold streak.
Step 3: Apply acid
Start with the acid matching the karat stamp (or 14K if no stamp). Place one drop directly on the streak.
Step 4: Read reaction (10-20 seconds)
- Streak stays bright gold = real gold at or above tested karat
- Streak fades slowly = slightly below tested karat
- Streak disappears or turns green/brown = below karat or fake
Step 5: Confirm with second test
If streak faded with 14K, test fresh streak with 10K. If 10K also dissolves it, likely plated or base metal.
Step 6: Clean up
Apply baking soda paste to stone and drips, rinse with water, cap bottles tightly.
Color Chart
| Reaction | Meaning | Likely Material |
|---|---|---|
| No change—stays bright gold | Real gold at/above tested karat | 10K-24K gold |
| Slow fade (30+ sec) | Slightly lower karat | One step below tested |
| Milky/cream color | Heavy plating | Gold-filled |
| Green | Not gold | Brass |
| Brown | Not gold | Copper/bronze |
| Rapid dissolve (<5 sec) | Fake or far below karat | Costume jewelry |
Pro Tips for Accuracy
- Make fresh streak for each test—residue skews results
- Replace acid annually once opened (weakens over time)
- Test multiple spots on same piece (plating wears unevenly)
- Cross-check with magnet first (real gold is non-magnetic)
- For high-value items, combine acid + electronic tester
Common Mistakes
- Skipping the hallmark check before choosing acid
- Testing plated jewelry on surface only (file through plating first)
- Using too much acid (one drop is enough)
- Reading results after 30 seconds (reaction is best at 10-20 sec)
- Reusing droppers between solutions
When to Use a Professional Assayer
Send pieces for professional testing when:
- Value over $2,000
- Suspected sophisticated fake (tungsten core, etc.)
- Buying bulk scrap that needs documentation
- Insurance paperwork required
FAQ
Is it safe for the jewelry?
Yes—when done on the stone (not directly on jewelry), only the transferred streak reacts.
How accurate is it?
95%+ accurate for real vs fake and identifying karat within one step.
How long does acid last?
Sealed: 2-3 years. Opened: replace within 12-18 months.
Can I test white gold?
Yes, same method. Rhodium plating is thin enough that streak captures the gold alloy.
What about 24K?
Pure gold needs aqua regia (nitric + hydrochloric mix), not standard nitric acid.
Happy to answer questions if anyone has specific testing scenarios!