Tarnish occurs on gold jewelry when the gold is exposed to air and oxidizes. Tarnish is a natural occurrence on all gold that is not pure. Some folks like the look of aged, tarnished 10K and 14K gold (called a patina).
Yellow gold is described as such because of its yellow colour which is a result of it being alloyed with silver and copper. 9 carat yellow gold is often a lighter yellow colour than 18 carat yellow gold, which is more of a rich and intense yellow due to its higher gold content.
10K gold is the least pure, least expensive, yet most durable, form of gold used widely in jewelry today. With its 41.7% gold purity, it's the most impure gold available on the market that can still legally be called “gold” in the US and most other countries.
Over time, there is a chance that your 10K gold jewelry might tarnish a bit. The tarnish is due to the metal alloy in its composition. However, you can bring back the shine by buffing it out carefully. Taking care of this gold is as simple as taking care of your other gold jewelry.
When you see a yellow sheen on your white gold jewelry, it is not the result of oxidation or another chemical reaction, meaning the metal does not actually change color. The outer layer of rhodium slowly wears away over time, eventually revealing the creamy-yellow color of un-plated white gold.
Pure gold (24K or 999) has a rich, nearly orange-yellow colour, however gold rarely occurs in nature in pure form. It generally grows as a crystal structure including other elements, like silver or copper.
Pure . 999 gold is bright yellow and is 24k. That means 24 parts out of 24 part are gold. Since 24k gold is quite soft, most jewelry gold is alloyed; other metals are added to pure gold and this gives it strength and will affect the color.
Most standards around the world identify anything with less than 41.7% or 10 karats of gold as fake. The most reliable way to identify whether your item is real gold, or not, is to have it appraised by a certified jeweler.
As we mentioned above, both 10k and 14k solid gold are fully tarnish-resistant, waterproof, and can be refinished and polished forever—but 10k solid gold goes one step further on durability.
10k gold is the cheapest form of gold that's still commonly used in jewelry. If you're looking for the least expensive option, this is your best bet.
Showering with 10k gold jewelry is generally safe, as 10k gold is a durable metal that can withstand exposure to water and moisture.
Price & Value
There is no price value difference between the actual gold in white and yellow gold jewellery, as long as it is hallmarked at the same carat weight.
Much like rust on a piece of metal, oxygen and sulfur are contributing factors to gold tarnishing. When moisture mixes with oxygen and sulfur compounds in the metals mixed with the gold, corrosion will take place on the surface causing a tarnished look.
The American Heritage Dictionary defines the color metallic gold as "A light olive-brown to dark yellow, or a moderate, strong to vivid yellow." Of course, the visual sensation usually associated with the metal gold is its metallic shine.
The implication of this data is that while 10k gold is significantly cheaper than high-karat variants, it is still quite valuable, retailing for slightly higher than half the price of the expensive 18k variant.
Fill a cup or bowl with water and carefully drop your gold piece into it. If the gold is real, it will sink to the bottom of the cup. If it's fake, it will float to the top or hover in the middle of the cup.
Gold Alloys Are Magnetic
This includes 18k gold, 14k gold, 10k gold, and even white gold. There are different alloys of gold. The most common metals that are alloyed with gold are zinc, copper, nickel, iron, cadmium, aluminum, silver, platinum, and palladium.
The three numbers represent the percentage purity. For example, the marking '417' means 41.7% gold, which is 10 karats. Using this same format, 14 karat pieces are marked '583' (sometimes '585') and 18 karat pieces are marked '750,' and so on.
Drop a small amount of liquid nitric acid on that scratch and wait for a chemical reaction. Fake gold will immediately turn green where the acid is. Gold-over-sterling silver will become milky in appearance. Gold will not react to the nitric acid.
Because it has a lower gold content it's stronger, and less likely to scratch, scuff or bend. A second advantage is the price - it's less expensive than 14k because it has less gold. However, one thing to note with 10k is that the color can be less vibrant yellow than 14k gold.
To keep its shine, you should clean your jewelry regularly with a solution of 10-parts warm water and 2-parts dish soap. A few extra tips: Soaking is the key: per Real Simple, you should soak your gold jewelry pieces for 3 hours and then scrub them gently with a very soft brush.