1. Introduction to the gold filled jewelry
The joining of a base metal with an outer layer of gold has played an important commercial role in the jewelry industry and their related trades for over 150 years. Gold filled jewelry, also known as “rolled gold” or “rolled gold plate” is composed of a solid layer of gold bonded with heat and pressure to a base metal such as brass (i.e. 90% copper and 10% zinc). Some high quality gold filled jewellery have the same appearance as 14 karat (58%) gold. In the USA the quality of gold filled jewelry is defined by the Federal Trade Commission. If the gold filled jewelry layer is 10 kt fineness the minimum layer of karat gold in an item stamped GF must equal at least 1/10 the weight of the total item. If the gold filling jewelry layer is 12 kt or higher the minimum layer of karat gold in an item stamped GF must equal at least 1/20 the weight of the total item. The most common stamps found on gold filled jewelry are “1/20 12kt GF” and “1/20 14kt GF”. Also common is “1/10 10kt”.
“Double clad” gold filled jewellery sheet is produced with 1/2 the thickness of gold on each side. 1/20 14Kt double clad gold filled jewelry has a layer on each side of 1/40th 14Kt making the total content of gold 1/20. The thinner layer on each side does not wear as well as single clad gold filled.
The process for creating gold filled jewellery sheet stock was developed by the industry to help reduce costs for jewelry without sacrificing their perceived beauty, durability, and long term wear.
By the Federal Trade Commission, gold filled jewelry, even with daily wear, can last 2 to 10 years but will eventually wear through.
However, The gold layer on gold plated jewelry varies greatly depending on manufacturer, so there is no single, simple comparison. Gold filled jewelry are 50 to 100,000 times thicker than regular gold plating, and 17 to 25,000 times thicker than heavy gold electroplate.
In China, by the General Administration of Quality Supervision, Inspection and Quarantine of China (AQSIQ), it has different definition for gold filled jewelry, it has not strict percentage of the weight of total item, its gold layer is from 5 – 10 microns. Even this thickness layer, this gold filled jewellery has good quality, can wear 2 – 3 years,even longer time.
2. Gold filled jewelry manufacturing process
Gold filled jewelries are created utilizing a process that starts with brass on which a thin sheet of karat (such as 18 karat) gold of the desired thickness has been “welded”. The process begins by carefully fitting the brass under a gold sheet of the desired karat alloy and thickness. They are then placed in a air tight steel enclosure that has a carefully controlled atmosphere. The edges of the two metals are covered with a flux type paste to help protect them from oxidation and scaling. Within a gas fired furnace, the brass and gold sheet are rapidly heated to a suitable welding temperature of about 900 degrees centigrade. It is then removed and is immediately “pressed” in a hydraulic press at about 2500 psi. The attachment weld between the gold and brass substrate is achieved by “alloy diffusion” (see chart a). This occurs because the atoms on the outer surface of each metal substrate collide and combine with each other to form a strong “alloy based” metallurgical bond.
The process continues by rolling the welded composite of gold and brass in a rolling mill. Combined with annealing (a heat treat process that softens the brass for the rolling mill process) the welded bond between the gold layer and brass is further enhanced by alloy diffusion that occurs from additional compression from the rolling mill process. The resulting weld is so strong that the finished gold filled sheet stock can be formed, fabricated and soldered without any risk of delamination.
Once the gold filled sheet is welded, additional finishing operations are needed. The sheet stock is “finished rolled” to the precise commercial gauge. Additionally, the surfaces are cleaned and all edges are trimmed to the desired widths and inspected prior to final shipment to the manufacturer.
3. The types of cladding for gold filled jewelry
The placement of the gold filled sheet layer onto the brass is also referred to as “cladding” (see chart b). Single clad gold filled jewellery has a gold sheet welded to the side of the brass which is intended to be the decorative side or “show surface”. Double cladding as its name implies has a sheet layer of gold welded to both sides of the brass. Typically double clad gold filled sheet stocks are used on items to prevent any discoloring or to enhance its value (i.e. cigarette case). Since the edges of the gold filled sheet stock are sometimes exposed, supplementary gold plating is often necessary to “seal” the brass core to prevent any chance of corrosion or discoloration.
Round gold filled wire and hollow tube stock have a layer of welded gold fused completely around a core of brass. This type of gold filled stock can be used in the earrings jewelry.
4. The commercial thickness for gold filled jewelry
In practice, most gold filled jewelry utilize an outer layer of gold that is between 10 karat and 18 karat in fineness. Depending on the usage, the thickness of the gold sheet varies. Thicknesses for imitation jewelry, such as cuff link, bracelets, and earrings will range from 15 to 100 microns.
As thin as this may seem, the decorative show surface on many well executed gold filled jewelry can last anywhere from 2 to 10 years! It is not unusual to observe reasonably intact gold filled surfaces on vintage jewelry manufactured well over 20 years ago.
5. The commercial designations and markings
In USA, the Federal Trade Commission (FTC) suggests that gold filled jewelry should equal 1/20th of the total weight of the finished item. As an example, a bracelet marked as “1/20 14k GF” with a total weight of 60 grams (2oz.) would mean that there should be at least 3 grams of 14 karat gold (60 grams divided by 20) utilized in the outer clad layers of the finished item. The remaining 57 grams could be comprised of a non-gold base metal material, hinge hardware and solder used in the fabrication of the piece.
However, according to the definition of the General Administration of Quality Supervision, Inspection and Quarantine of China (AQSIQ) for gold filled jewelry, it has a gold layer from 5 – 10 microns, it is usual to see gold filled jewelry stamped as “18K GF” or “14K GF” in jewelry marketing, but it has to remove the “1/20″ stamp. So a typical legal marking might then appear as “18K GF” in China.