What is a master alloy and how does it differ from a conventional alloy? And why is the use of master alloys so important in the jewelry industry? That’s what we’re going to find out in this article.
Most of the alloys in our catalog meet the definition of a master alloy, and the question arises as to what exactly lies behind this definition.
An alloy is a compound consisting of two or more elements, at least one of which is a metal. The properties of an alloy, such as hardness, strength, and even color, are usually different from those of the elements that make it up. For example, copper and tin, both of which are relatively soft, make up the more resistant bronze.
A master alloy is a special type of alloy designed to be added to a pure metal – in our case, gold or silver – to change its properties. A pre-master alloy is a master alloy from which a fundamental element has been removed. In our field, it is usually a master alloy from which silver has been removed for logistical reasons.
Why is it necessary to use a master alloy?
Most pure metals are not suitable for engineering applications. Pure gold, for example, is extremely soft; this property makes it easily malleable and is one of the reasons for its success in jewelry making, but a piece of pure gold jewelry would easily deform if handled carelessly and would not have adequate wear resistance. The same considerations apply to silver. Therefore, pure gold is usually converted to a gold alloy, in standard ratios expressed in quarter-twentieths or carats (K).
Until World War II, the most popular alloys consisted mainly of three elements: Gold, Silver and Copper.
As technology advanced, the jewelry industry demanded higher and higher performance from alloys, which led to the need to investigate the use of new elements that could be added to precious metals and fundamentally, alter their properties. So we moved from alloys consisting of two or three elements to new formulations containing even ten elements, increasing the complexity of the product.
What properties can a master alloy influence?
Once a master alloy is added to the precious metal, it can affect:
A property particularly sought after by gold users, whose color can be changed to pink, gray-white or various shades of yellow.
Perhaps the most important characteristic, since gold and silver are relatively soft in their pure state. Hardness is controlled by master alloys, both directly by the mere addition of alloying elements and indirectly by making the precious metal suitable for hardening heat treatments.
The melting temperature
This is another important parameter that is useful in certain applications if it can be controlled. Suppose we need to braze a joint, we can use a certain alloy for this purpose, which must melt at a lower temperature than the metal that forms the edges of the joint; in this way we achieve a particular type of brazing called brazing.
Controlling the melting temperature is also important when casting wax for stones, as too high a temperature for the metal could damage the stones beyond repair.
Size of the crystal grain
By using certain elements called grain refiners, the internal structure of the metal can be made more compact, which greatly improves some aesthetic and technological aspects, we talked about them here.
Flow ability is an important factor, especially in investment casting applications. It can be described as the ability of a liquid metal to faithfully fill an intricately shaped pattern such as a grid or watermark.
In general, the fluidity of precious metals increases with casting temperature, but this can lead to some side effects, such as interference between the metal and refractory material or vaporization of low-melting alloying elements. To overcome these problems, certain elements such as silicon can be added to the master alloys for lost wax casting, which are able to increase the flow ability of the metal in the liquid state. In this article, we have talked in detail about the role of silicon in investment casting alloys.