About Bi-Metal

(Images courtesy of Hauser & Miller customers' Barbara Terrell and Sydney Lynch.)

18K Yellow on Sterling Silver - 22K Yellow on Stering Silver

  To better understand the history, traditional uses, and manufacturing technique of mechanically bonded metals we are including the following paragraphs from pages 16 and 17 of the Handy Book of Precious Metals by Handy & Harman.

GOLD FILLED

  Gold for the millions: The possession of gold in any of its forms was, until recently, a rather exclusive privilege. However, an “accident” in a silversmith’s shop more than 200 years ago set the stage for the popularization of gold, putting it within the reach of millions. This accident led to the development of gold filled, which is an overlay of 10 karat or better bonded by heat and pressure or reinforcing metal.

THE ORIGIN OF GOLD FILLED

  The silversmith was Thomas Bolsover, of Sheffield, England, who, while using a copper coin as a shim to hold a silver knife in a vise, discovered that after several hours of clamping, the copper had fused to the silver. This mechanical bonding process would later be used to fashion fine heirlooms (using minimal amounts of silver bonded to less costly metals) which not only exhibited the beauty of a precious metal, but was also affordable to wide stratum of the population.
  The technique of mechanical bonding, taking its name from the place of its discovery, was called the “Old Sheffield Process” and when the amalgam was produced with gold or silver, the end product was called “Gold Filled” or “Silver Filled” respectively.

HOW GOLD FILLED IS MADE

  Gold filled is produced by fusing a layer of karat gold to a suitable supporting metal (or alloy), using equipment that carefully controls pressure, heat, and time. The bond produced is a permanent one.
Next comes a series of rolling operation, which compresses the strip into a sheet. Repeated rolling reduces the thickness of the material in such a way as to preserve the proportionate thickness of the gold and the supporting metal. Repeated rolling increases the density of the gold, so that it becomes harder and more durable.

REQUIREMENTS FOR GOLD FILLED

  Gold filled products must consist of at least one layer of karat gold. The minimum karat for this layer is 10 karat gold. This must represent at least 1/20th the total metal weight. Rolled gold plate is material consisting of layer or plating of 10 karat gold or better. The proportionate weight of the karat gold may be less than 1/20th (1/30th, 1/40th, or as the case may be).

18K Yellow on Sterling Silver Bi-Metal

HALL MARK

1/20 18K/Stg GF

DESCRIPTION AND USE

  A layer of 18 karat gold alloy with a rich yellow color is bonded with sterling silver to form a sheet of precious metal with two distinct surfaces. The gold layer is similar to that of most gold filled products and has comparable working characteristics. However, such surface treatments as engraving, scraping, folding, and twisting can be used to accent the two surfaces.

COMPOSITION

MELTING POINT

ANNEALING TEMPERATURE

1140 °F to 1300 °F

SOLDERING

On gold surface use: 14K or 18K yellow easy (soft) solder
On sterling surface use: easy or medium silver solder

MECHANICAL PROPERTIES

Similar to sterling.

DENSITY

STOCK SIZES

Sheet and circles: 20 and 24 gauge
Sheet: minimum 1" x 1" maximum 3" x 12"
Circles: 1/4" diameter to 2" diameter

22K Yellow on Sterling Silver Bi-Metal

HALL MARK

1/8 22K/Stg GF

DESCRIPTION AND USE

  A layer of high karat gold alloy (22K) with a bright yellow color, close to that of fine gold, is bonded with sterling silver to form a sheet of precious metal with two distinct surfaces for finishing. The gold layer which is two to three times thicker than most gold filled products gives this product more workability than usually associated with gold filled products. Such surface treatments as engraving, scraping. Folding and twisting can be used to accent the two surfaces, as well as burnishing and chasing which are possible because of the heavier layer of gold.

COMPOSITION

MELTING POINT

ANNEALING TEMPERATURE

1140 °F to 1300 °F

SOLDERING

On gold surface use: 14K or 18K yellow easy (soft) solder
On sterling surface use: easy or medium silver solder

MECHANICAL PROPERTIES

Similar to sterling.

DENSITY

STOCK SIZES

Sheet and circles: 18 and 24 gauge
Sheet: minimum 1" x 1" - maximum 3" x 12"
Circles: 1/4" diameter to 2" diameter