Bi-Metal
(Images courtesy of Barbara Terrell and Sydney Lynch.)
Description and Use
A layer of 18 karat gold alloy with a rich yellow color or 22 karat gold alloy with a bright yellow color is bonded with sterling silver to form a sheet of precious metal with two distinct surfaces. The 18K gold layer is similar to that of most gold filled products while the 22K is two to three times thicker than gold filled products giving it more workability. Surface treatments, such as engraving, scraping, folding, and twisting, can be used to accent the two surfaces.
Composition
18K
- By weight: 5.00% 18K and 95% Sterling
- By volume: 3.38% 18K 96.62% Sterling
- 24 gauge: .00068" 18K layer and .01942" Sterling
- 20 gauge: .001082" 18K layer and .030918" Sterling
- 26 gauge: .00054" 18K layer and .01546" Sterling
22K
- By weight: 12.50% 22K and 87.50% Sterling
- By volume: 7.63% 22K and 92.36% Sterling
- 24 gauge: .001534" 22K layer and .018565" Sterling layer
- 18 gauge: .003076" 22K layer and .037223" Sterling layer
Density
18K
- Specific gravity (GM per cubic CM): 10.53718
- Ounces per cubic inch: 5.5516
- Ounces per square inch:
20 gauge: .17765"
24 gauge: .11159"
26 gauge: .08883"
22K
- Specific gravity (GM per cubic CM): 10.9367
- Ounces per cubic inch: 5.7621
- Ounces per square inch:
18 gauge: .23221"
24 gauge: .11583"
Melting Point
- 18K: Solidus: 1620 °F / 882 °C - Liquidus: 1715 °F / 935 °C
- 22K: Solidus: 1780 °F / 971 °C - Liquidus 1840 °F / 1003 °C
- Sterling: Solidus: 1435 °F / 780 °C - Liquidus: 1640 °F / 890 °C
- Between 1600 °F and 1650 °F silver side will begin to flow and reticulate below the gold layer.
- Annealing temperature is 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
Stock Sizes
- Sheet and circles: 18K: 20 and 24 gauge - 22K: 18 and 24 gauge
- Sheet: minimum 1" x 1" maximum 3" x 12"
- Discs: 1/4" diameter to 2" diameter
