Questions and Answers about the Basics of White Bronze

Question

What is white bronze and how is it used? 

Answer

White bronze is also called tri-alloy or tri-metal. It is an alloy of copper, tin and zinc. It is used as a replacement for nickel in the manufacturing of jewelry and items that require a barrier layer between a base metal and a gold layer. It is estimated that anywhere from 10 to 20 percent of people are allergic to nickel when in contact with the skin, hence the need to replace nickel in jewelry and other items that might come in contact with skin.

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The white bronze alloys that contain between 40 to 60 percent tin are, as the name implies, white in color, tarnish-resistant and are moderately hard. Because of the concerns about nickel in the environment, this material will no doubt see greater use in the future.

There is an excellent article available on PF Online titled “White Bronze, Copper-Tin-Zinc Tri-Metal: Expanding Applications and New Developments in a Changing Landscape,” giving a very complete discussion of the latest developments with white bronze.

Question:

At what thickness is white bronze non-porous? If this was to be used after acid copper plating as a barrier before gold plating, would the non-porous thickness be enough to stop migration? 

Answer:

White bronze, often called Speculum, is used as a replacement for nickel in the manufacturing of jewelry and items that require a barrier layer between the base metal and the gold layer. The white bronze alloys contain between 40-60% tin are, as the name implies, white in color, tarnish resistant and are moderately hard. Because of the concerns about nickel in the environment, this material will probably see greater use in the future.

When white bronze is deposited as a barrier layer, the thickness of the deposit is usually between three and five microns. Whether a thinner layer would be adequate, I honestly don’t know.

There are a number of papers that have been published on this topic. A quick search of Surface Finishing Abstracts website comes up with 31 references on white bronzes.