The story of gold : Gold alloying: General principles

The story of gold : Gold alloying: General principles

The metals that are accumulated with gold accept a abstruse aftereffect on its color, atmosphere and hardness. The action of accumulation added metals (usually "base" metals) with gold is alleged "gold alloying," and the metals acclimated in the action are usually alleged alloying elements. When the final admixture contains added than 50% gold, the admixture is usually referred to as a "gold alloy."

The best accepted alloying elements acclimated in the United States are silver, copper, nickel and zinc. Each of these metals alters the color, tem- per, acerbity and annealing characteristics of the gold. Although the metallurgical accord amid gold and its alloying elements is absolutely complex, in accepted the amount of change, which can be imparted to the gold, is accompanying to the allotment of abject metal used. The college the allotment of abject metal, the greater the change in the concrete characteristics of the gold. Obviously, if identical amounts of the aforementioned abject metal are added to according weights of karat gold specimens, the abject metal will accept a added arresting aftereffect on the lower karat gold than on the college karat gold.

Although accomplished jewelers and goldsmiths apperceive what appropriate qualities they appetite – and are accustomed with the use of alloying elements to accomplish them – it may be advantageous to abridge how these alloying elements adapt the assorted backdrop of gold.

Color

Jewelry golds range from light yellow through deep yellow to reds and greens, and also include a family of whites.
Silver: As the proportion of silver increases, gold changes in hue from yellow to greenish-yellow, to white.
Copper: As copper content in- creases, the gold becomes redder in appearance.
Nickel: Nickel has the effect of whitening gold. The so-called "white golds" substitute nickel for silver.
Zinc: Zinc is considered a "decolorizer," and is used to convert some red golds (copper alloys) into a more yellowish tone by substitution of zinc for some of the copper and silver.

White golds

Historically, the white golds were alien to alter platinum. A archetypal admixture acclimated was a 19%K gold, with about 81% gold, 16% nickel and 3 % zinc. At the lower karat levels, the added nickel fabricated the admixture difficult to work. At 18K, some cop- per was capital for workability, with abundant amounts bare for 14 and 10 karat alloys. Because alone baby amounts of chestnut could be acclimated in adjustment to absorb a white color, zinc was added as a softener, acceptable the whitening aftereffect of nickel while abbreviation the charge for red copper. The use of zinc, how- ever, was bound by its addiction to access blaze arise – the arise that sometimes occurs about the atom boundaries of awful formed nickel-bearing white golds aloft annealing. This is a actuality able-bodied accepted in the industry, and is affected by heavy, compatible alive of the metal afore annealing.

Characteristics and calefaction treatment/annealing

 As we’ve noted, karat golds are fabricated in red, yellow, blooming and white as accepted colors. Shades of these colors are accessible as appropriate compositions.

Even aural a distinct blush standard, however, the agreement and the concrete backdrop of the karat gold will alter considerably. In chicken gold, for example, it is accessible to access ductile, abysmal cartoon gold for hollowware and toilet ware; a corrosion-resistant bounce banal for bubbler pen nibs; a hard, high- compactness backbone gold for handmade casework; bounce atmosphere wire for pin tongs and springs; alloys which casting well, and others with above enameling properties.

Yellow golds action the widest alternative of backdrop and compositions. There is a chicken gold agreement for about every adornment requirement. The red golds, as a group, accept a addiction to burn added rapidly back acrimonious (in soldering or annealing) because of their aerial chestnut content. Karat golds can be quenched in baptize from the annealing temperature. This will accord a softer and added compatible admixture than air-cooling. It should be acutely understood, how- ever, that abatement from the annealing temperature agency drop- ping or coast the karat gold into the baptize while the gold is still at temperature. Delaying the abatement (allowing the gold to air-conditioned off afore coast it into the water) can account non-uniformity of hard- ness throughout the allotment and the gold will not attain best softness.

Since it is accessible to amalgamate gold by adopting the annealing temperature, the user of karat gold should apperceive the able annealing temperature for the accurate agreement actuality processed. In general, red, blooming and chicken gold alloys are annealed at 1200’F. (649’C.).

In annealing wrought metals, under-annealing may actualize directional properties, and over-annealing may aftermath "orange peel" surface. On the added hand, in the annealing of casting pieces above-mentioned to precipitation hardening, almost college temperatures and best times of amalgamate are suitable.

Annealing and hardening ambit accept been formed out for anniversary accepted alloy, and best after-effects will be acquired by afterward the manufacturer’s recommendations closely. 

Controlling finish 

 The aerial calefaction of annealing and soldering may account apparent oxides, or a action alleged "fire", actualization as brownish streaks or blotches about the acrimonious area.

Surface oxides can be removed by a 10 % sulphuric acerbic band-aid acrimonious to about 180 F. (80 C.). Eight genitalia baptize to one allotment nitric acerbic brought to baking may additionally be acclimated for 10K and 14K golds. Where the sulphuric acerbic does not abolish the calibration readily a baby bulk of sodium bichromate may be added.

Fire affects decidedly the lower karat golds and red golds because of their college chestnut content. It can be prevented during heating by a blanket of Handy 8z Harman’s Handy Flux, which helps assure the metal apparent from oxidation. Blaze that is too abysmal for cutting out can be removed by dipping the gold briefly in a algid 25 % nitric acerbic solution.