2, different colors: because thousands of gold contains less gold, the color of thousands of gold will be lighter than thousands of gold. But in fact, 99.9% and 99.99% are not much different in appearance.
3. Different hardness: the higher the purity of gold, the softer it is, and pure gold is softer than pure gold. In addition, when making jewelry, 99.99% generally choose no welding material, while 99.9% gold jewelry will have one or two welding spots.
Extended data:
Precautions:
Gold jewelry should avoid contact with mercury-containing substances (red-purple liquid, thermometer), acid-base corrosive substances or other industrial waste gas. It may cause jewelry to be corroded, discolored, even brittle and pulverized, resulting in economic losses.
When taking a bath, washing your hair, washing your face, washing your hands or doing housework, you'd better take off your gold jewelry. This can not only prevent soap, detergent and chemicals in bleaching water from polluting the surface of gold jewelry, making it lose luster and produce spots, but also avoid deformation, fracture and falling off, especially when sleeping and washing.
18K gold jewelry contains other metal materials besides 75% gold content. These materials will change color when used for a long time because of their low corrosion resistance. Once this problem occurs, you can send it to the gold shop with relevant vouchers for professional cleaning of jewelry.
Baidu encyclopedia-gold