Testing Gold Karatage and Interpreting Marks
How can you determine the gold karatage of an item and learn if it’s gold-filled or plated? This simple technique will do the trick.
5 Minute Read
What Does "Gold Filled" Mean?
The term "gold filled" indicates a manufacturing process in which two thin gold sheets with a supporting piece of core metal form a sort of "metal sandwich" construction. This construction is then laminated with a brazing alloy into one inseparable sheet. After making this "fused ingot," the metalsmith places it in a rolling mill and rolls it to the desired thickness. This filling process must be accomplished mechanically in order for the product to be considered gold-filled.
Stamping indicates the gold content of the "sandwich" by weight and karatage. Thus, a gold-filled article stamped "1/20-14K" indicates that gold comprises at least 1/20 of the total metal content and that the gold sheet used was 14K.
What is Gold Plating?
Gold plating is an electrolytic process in which direct current is used to deposit gold on a host metal.
Many gold-plated articles don't have marks indicating the gold content by weight. Their marks only indicate plate karatage, like "14K GP or "10K Gold Plate," for example. You may find various markings in gold-plated areas. Many items contain marks such as RGP for "rolled gold plate" or HGP for "heavy gold plate."
Old gold watches with gold plating are rarely marked with the gold weight or karat. These watches are so heavy that, for economic reasons, they couldn't be covered with gold so as to constitute 1/10 or even 1/20 of the metal weight. However, these old watches are valuable. You can often find markings that indicate the expected years of wear, from 10 to 20 and even up to 25 years.
The jewelry industry also utilizes gold and silver epoxies for low-cost jewelry items. The technology here is so advanced that these epoxies need a careful look - and they often wear better than gold plating.
The Landis Procedure for Determining Gold Karatage
So then, how do you know if that old ring with no markings is gold? And, if it's gold, how do you know if it's at least 10K, the minimum for calling the item gold? How can you tell if it's 14K, 18K, or 24K? And is there any way to determine if that expensive-looking gold piece is gold filled, gold plated, or epoxied?
There's a refined laboratory technique using a series of chemicals. There's also a much simpler, less expensive way that was developed and announced by Harry Landis, Inc., a New York refiner.
Let's consider the Landis procedure and the equipment you'll need.
First, you'll need nitric acid.
Before going any further, heed this warning. Nitric acid is very dangerous when used carelessly. If you handle nitric acid with care, however, you'll have no problems.
Jewelers and precious metal specialists have used nitric acid for centuries with very few incidents, accidents, or casualties. Just keep in mind that this powerful acid can result in serious pain and injury. It will damage almost anything it comes into contact with. It's poisonous and deadly if ingested, even in trivial amounts. Use nitric acid only in a well-ventilated area and wear rubber gloves. Keep water readily available for a quick emergency rinse. Follow all the safety procedures recommended for nitric acid. The author and publisher take no responsibility whatsoever for any consequences if or when you use nitric acid.
For maximum safety for metal testing, you'll need:
- Two acid testing bottles with dip sticks (one for nitric acid, one for aqua regia)
- Two flat pieces of unglazed porcelain (one for 10K and 14K, the other for 18K)
- Pure-grade nitric acid
- A pumice stone
- A sample each of 10K, 14K, and 18K gold
- A small metal file
You'll use your samples of known gold karatage to compare against unknown metals.
Use an emery cloth to remove the glaze from a porcelain dish or saucer to create your porcelain testing stones. You can buy a pumice stone at a drug store. Most hardware stores or chemical supply houses can generally supply some nitric acid as well as the other items.
Yellow Gold Karatage Testing
To test for yellow gold, rub the metal in question on the 14K gold testing stone so that it leaves a mark or streak on the touchstone. Then, using the acid bottle dip stick, touch some nitric acid on the streak. Base metal (non-gold) will appear green or gray. 14K gold or better will remain unaffected.
Before proceeding to the next gold karatage test step, select an inconspicuous spot that won't mar the item's appearance. Take the file and make a tiny slot through the surface and into the base metal itself. Apply a light touch of nitric acid to the filed slot and watch carefully. Compare your results to the table below.
|Color Change in the Slot||Base Metal|
|No change||14K or better|
|Green color||A base metal or brass|
|Dark gray color||Silver alloy|
If the base metal is white and doesn't react with the acid, it could be iron or steel.
Using Aqua Regia for Gold Karatage Testing
For additional, higher gold karatage testing, professionals use a chemical called aqua regia. You can purchase this chemical separately. Follow all the safety procedures recommended for this material. Use aqua regia only on the 18K touchstone.
On the stone with the aqua regia, scratch or streak marks made by 10K gold will disappear. Those made by a 14K mark will turn dark. Those made by an 18K mark will remain unaffected.
Cleaning the Touchstones
You can easily clean the testing stones by rubbing them with pumice under running water. Wipe them dry with any tissue. Just take care not to use the same area of pumice or the same tissue on different stones. If you wipe off the 18K stone and then use the same tissue on the 10K or 14K stone, the latter stones will be useless for any further testing.
White Gold Karatage Testing
You can also use the Landis technique to test white gold. However, use white gold samples of known karatage for applying streaks. Most white gold jewelry items are stamped with karatage.
Dr. Gerald Wykoff GG CSM
Dr. Gerald Wykoff is GG (Graduate Gemologist), a CSM (Certified Supreme Master gemcutter), educator, and author of several gemology books. He founded the American Society of Gemcutters in the 1980s and served for more than 10 years as the editor of its monthly magazine, American Gemcutter.
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