Because of my interest in theatre I have accumulated several history of costume books going back centuries. In the case of vintage jewelry my interests begin around 1840 to the 1960’s.

Jewelry construction has changed very little over the past 4000 years. It is a good idea to get a basic knowledge of jewelry construction and manufacturing techniques if you really want to accurately identify antique and period jewelry.

Hand Fabrication:
A piece is said to be handmade when a bench person makes the piece from start to finish. They may use purchased tubing or sheets of gold or may elect to alloy the metal and roll the gold themselves. The jeweler can start with a sketch of their own or one provided by a designer and then select the stones and materials or they can begin with the stones and let them dictate the size and flow of the finished piece.

Casting:
This method usually starts with an existing piece of jewelry or a carved wax form that a mold model can be cast from. A rubber mold is made by packing the model with a special rubber material and vulcanizing it in a mold maker.When it is finished the model is cut out and you have an exact duplicate of the orginal piece. How can you tell if the piece you are looking at has been cast? Look closely at the back side of the piece. Sometimes you can detect the tell-tale flow lines of casting or you may see a bubbly effect or porosity marks.

Die Striking/Stamping:
To be simply put die striking and stamping is the movable force(the metal) meeting the immovable object(the steel die). A designer creates an original by hand, then metal dies are made from the piece. The jewelry is manufactured by stamping the hard metal dies into the softer precious metal. Die-struck jewelry is denser and more durable than cast jewelry, and it allows a higher polish however, stamping is more expensive than casting because of the equipment, factory space and time involved in making dies.

Electroforming:
Compared to the previous processes this one is considered a “modern” process for making jewelry. It was first patented in England in the 1840’s. In the 1850’s and throughout the end of the century it was used to make copies of ancient and Celtic jewelry. Popularity for this process waned for almost 100 years but has now come back into favor.
It is basically a process in which pure or carat gold is electroplated onto a shaped former. This can be a low melting point metal but more recent technology developments now enable electroforming onto a wax model, such as produced for lost wax casting. Control of both consistency and uniformity of thickness as well as carat-age is very important in a mass production situation where 50 -75 pieces may be electroformed simultaneously in the bath. This is achieved by computer control of the plating bath. Generally electroformed articles will be around 100 -150 microns thick and even up to 250 microns for large items. The wax or metal former is removed at the end of the process.

There are 2 electroforming technologies available. One produces a deep yellow gold-copper-cadmium alloy deposit and the other a paler yellow gold-silver alloy, both in the range of 8 to 18 carats. Electroforming of pure gold is also carried out and is particularly popular in the Far East. When plating is done at high plating rates, a textured surface is produced which does not require further finishing.

White Metal Spin Casting:
Much of the costume or fashion jewelry made to day uses this method of construction. Because old costume jewelry is so collectible, it is important to have a some understanding of how it is made.
The white metal used in this process is an alloy or mixture of tin, lead, bismuth, antimony and cadmium. The tin content can vary from 17-92% depending on the quality of the piece. Many good quality white metal pieces have an 88% tin content. White metal melts at 520 to 420 degrees. Just like other casting methods this one starts with a model of the piece to be produced. From this piece a model mold is made. Since 1937, rubber was the choice material for molds. Before that year the molds were made of bronze.