Gold Acid Test Colors Explained | Karat-by-Karat Guide
Share
You've applied the acid. Now what? Understanding gold acid test colors is what separates a confident result from a confusing smear on a testing stone. This guide explains exactly what happens when acid meets real gold versus fake gold, and walks you through every karat level so you know what you are looking at.
Safety first: Always use acid testing solutions with gloves, eye protection, and good ventilation. These are strong acids that can cause burns and irritation.
What Happens When Acid Touches Gold
The chemistry behind acid testing is straightforward. Testing acids are nitric acid solutions calibrated to specific concentrations. Gold is one of the least reactive metals on earth — it resists acids that dissolve most other metals. The higher the karat (meaning the higher the percentage of pure gold), the more resistant the piece will be.
When you apply acid to a gold mark on a testing stone, one of three things happens:
- No reaction — The mark stays intact. The piece is genuine gold at or above the tested karat.
- Partial reaction — The mark fades slowly over 20–30 seconds but doesn't fully disappear. This means gold is present, but at a lower karat than the acid you used. A slow, gradual fade is normal for pieces that are slightly under-karat. Instant disappearance means the piece is well below the tested level or not gold.
- Full dissolution or discoloration — the mark disappears or turns a dark color quickly. The piece is below the tested karat, plated, or not gold at all.
Gold Acid Test Color Reactions by Karat
The color you see depends on the specific acid used and the metal present. Here is what to look for when using a standard karat acid test kit:
9K and 10K Gold
These lower-karat alloys contain a significant percentage of base metals (copper, zinc, silver). When 14K or 18K acid is applied, the mark will dissolve or turn greenish-brown fairly quickly. When tested with 10K acid specifically, genuine 10K gold will hold up or show only a faint cream/tan reaction.
12K Gold
Relatively uncommon today, 12K gold (50% pure) sits in the middle range. It will hold against 10K acid but dissolve noticeably under 14K acid.
14K Gold
The most common gold karat in American jewelry. When 14K acid is applied to a genuine 14K mark, you'll see little to no reaction — the mark stays largely intact. Against 18K acid, a 14K piece will show a mild reaction, fading somewhat.
18K Gold
Widely used in European and high-end jewelry (75% pure gold). A real 18K piece will hold firm against 18K acid and show minimal change. Under 22K acid, it will react and fade.
20K and 22K Gold
High-purity gold common in Middle Eastern, Indian, and Southeast Asian jewelry. 22K acid is quite strong. Genuine 22K gold holds up; 18K and below will dissolve clearly.
Reading a Tricky Result
If a mark holds under 14K acid but fades quickly under 18K acid, you're likely looking at 14K–16K gold. Use the table below and compare reactions to narrow down exactly where your piece falls.
Full Color Reference Table
Scratch your piece on the stone, apply the matching acid, then compare whether your mark reacts like the "matching acid" column or the "higher acid" column.
| KARAT | PURITY | REACTION TO MATCHING ACID | REACTION TO HIGHER ACID |
|---|---|---|---|
| 9K | 37.5% | Holds; slight cream tint | Dissolves/turns green-brown |
| 10K | 41.7% | Holds; minimal reaction | Fades noticeably |
| 12K | 50% | Holds | Fades or dissolves |
| 14K | 58.5% | Holds; cream to no change | Mild fading |
| 18K | 75% | Holds; little to no change | Fades or dissolves |
| 20K | 83.3% | Holds well | Slight fading |
| 22K | 91.7% | Holds firmly | Mild reaction |
Tips for Reading Results Accurately
Use Good Lighting
Subtle color differences — a cream tint versus a green tint — are easy to miss under poor lighting. Test near a window or use a bright lamp.
Compare to a Known Reference
Most acid test kits include reference needles made of specific karat gold. Scratch the reference needle beside your unknown piece and apply acid to both marks at the same time. Compare the reactions side by side.
Wait the Full Reaction Time
Don't judge the result after only a few seconds. Let the acid sit for 20 to 30 seconds, or follow your kit instructions. Some slower reactions reveal themselves over time.
Keep Your Testing Stone Clean
Residue from previous tests can contaminate new ones. Rinse the stone with water between tests and let it dry.
Gold-Plated Items
Plated items are where acid testing earns its reputation. When you scratch through the plating and hit the base metal underneath, the acid will react strongly — often turning dark green or brown immediately. If only part of the scratch reacts dark green or brown and part stays lighter, you may be hitting both plating and base metal in the same line — a telltale sign of a plated piece. This is exactly what you want to know before paying full price for a piece.
Read Results with Confidence
Once you understand the color reactions, acid testing becomes second nature. The Techneak Gold Testing Kit from TrueAssay.com includes karat-specific acids, a quality testing stone, reference needles, and a clear instruction guide — so you're never guessing what the reaction means. Whether you're testing one ring or fifty, you'll have accurate answers in minutes.
Related: How to Test Gold at Home (Complete 2026 Guide)
Related: How to Test Gold with Nitric Acid: Step-by-Step Safety & Accuracy Guide