White gold alloy compositions

Abstract

A nickel- and palladium-free 14-karat white gold alloy composition consists essentially of the following parts by weight: about 58.34% gold, about 35-40% silver, about 0.5-1.80% tin, and about 0-0.75% germanium.

Description

TECHNICAL FIELD [0001] This invention relates to novel white gold alloy compositions that exhibit the desirable properties of improved color and workability, but without the use of nickel, palladium or platinum. BACKGROUND ART [0002] Many white gold alloy compositions are known. Most are used in making jewelry. There is no standard or specification for the composition of white gold. Many white golds alloys contain nickel or palladium as the bleaching agent. Silver, the whitest of all elements, can be used as the bleaching agent. However, in alloys above 9 karat (i.e., 37.5% gold), silver causes the alloy color to become greenish. Green gold typically includes gold, a high amount of silver, and a small amount of copper. [0003] When nickel is used as the main bleaching agent, the amount of nickel determines the whiteness of the gold. The main advantage of nickel is low cost. However, there are many disadvantages to the use of nickel. Nickel can cause an allergic reaction in approximat...

AI Technical Summary

Benefits of technology

[0016] One specific and preferred 14 karat white gold alloy composition consists of about 58.34% gold, about 39.66% silver, about 1.50% tin, and about 0.50% germanium. This composition is nickel-free (non-allergic) and palladium-free (moderate cost), and exhibits the desirable properties of excellent workability, good corrosion resistance (elimination of stress corrosion cracking), and a bright white color, which can possibly eliminate the need for rhodium plating.

[0017] Accordingly, the general object of this invention is to provide improved white gold alloy compositions.

[0018] Another object is to provide improved white gold alloy compositions that are non-allergic and nickel-free.

[0019] Another object is to provide improved white gold alloy compositions that are moderate in price and palladium-free.

[0020] Another object is to provide an improved white gold alloy composition, which has excellent workability, which increases productivity and reduces work stress.

[0021] Another object is to provide an improved white gold alloy composition, which has a bright white color and can be produced without the necessity to rhodium plate.

Problems solved by technology

However, there are many disadvantages to the use of nickel.

If an individual becomes sensitized to nickel, it becomes a lifelong allergy, and skin reactions can be quite severe.

This makes it more difficult to work the metal, and causes increased stress on the worker.

This can cause poor productivity in investment casting, due to gas porosity.

Such flash-type plating typically wears off with product usage, exposing the underlying white gold.

The main reason for flash plating is cost, as rhodium is very expensive.

However, this exposes the skin to higher nickel contents.

Nickel white gold also can cause a metallurgical problem known as stress corrosion cracking.

Stress corrosion cracking is caused by weak grain boundaries that occur in wrought product that is hard and under stress.

This is usually seen as broken or cracked prongs on rings.

Nickel white golds are also poor in their ability to be reused.

This causes a high amount of scrap, which needs to be refined and recycled with the associated costs.

However, there are some disadvantages to palladium white golds.

Currently, the price of palladium (about $230 per Troy oz.) has caused the cost of materials to rise to such an extent that usage and sales have fallen significantly.

Palladium prices have dramatic price swings, which create difficulty in consistent pricing at both manufacturing and retail.

High palladium white golds have high melting temperatures, and, consequently, fast solidification times. This limits productivity by limiting the number of units producible by investment casting technique at one pour.

Moreover, the high temperature can cause interaction when investment casting with typical investment materials.

This causes a sulfur gas to react with the silver (normally high content in the palladium alloys) to form silver sulfide on the product surface, which is very hard to remove.

The cost of refining the palladium in the white gold scrap produced, is expensive, usually between 15% and 25% of the palladium cost.

The cost of the rhodium plating is also a drawback.

The disadvantages of silver are the poor color (greenish), and the tendency to tarnish.