Tuning Your Gold
Have you listened to the difference the fine tuning makes in a good guitar or piano? Sure they might play alright almost regardless of the fine tuning. But for that wonderful harmony of strings we must have that last 1% of the tuning just right.
Like musical instruments alloy formulae can go back a thousand years and be just a few common metals. Or, they can be from today’s modern metallurgical wisdom. All create wonderful jewelry each and every day. It’s the match of method and alloy additives that makes for success.
O2
Oxygen is life to you, yet destructive to hot gold alloys.
Oxidation is the enemy of fine casting. It is to be avoided when possible and must be removed as best as possible to make the great pieces that sell well. This is the first motive to use additives at all.
Si
Silicon (and other deoxidizers) can benefit casting.
For those who cast 10kt or 14kt in ‘open air” with a torch or electric smelter that exposes the melt to the air, be sure to get an alloy that includes silicon or some deoxidizer. This gives you gold that beaks out less dark, less oxidized, and will re cast from sprue metal reliably. Here is why-When copper is hot it reacts with oxygen from the air easily. So for open air casting some clever alloy people learned to add silicon to the alloy. Silicon additives help because of the blocking effect on the copper oxygen chemistry. Remember copper is usually the highest metallic content in alloy next to the gold. In low karats or rose colors copper content can exceed the gold content. Silicon as a copper “deox” is great for torch casting, but it can cause enlargement problems in grain structure of the castings. That can mean brittle castings. This became the gold standard for years and years. These alloys are very common in the inventories of alloy dealers.
Bullet -Here is where silicon will impede your production.
a. The aforementioned larger grain size can be a problem for fabricators who mistakenly use casting gold for rolling. Fabrication process do not need deoxidation. Pickling after annealing and polishing take care of that.
b. Stone in place castings are brittle because they are cooled slowly rather than quenched. This along with the silicon encourages grain size growth.
c. Eighteen karat gold in general should not contain silicon. There is so little copper, the benefits are outweighed by the risks of brittle casting.
Sometimes a caster with very modern equipment needs a different, non silicon alloy-Alloys for closed system induction are different than the rest.
Beyond deoxidizing
Additives do many subtle jobs. Grain refining is how we manipulate grain size usually trying to get it smaller. This is done with high temperature exotic elements. Fluidity and casting flow temperature can be adjusted with additives. Some ordinary materials like zinc, sometimes very exotic stuff like lithium.
Electric casting with some form of atmosphere control like nitrogen or argon in the crucible during heating and casting is common at larger jewelry factories. This technology was originally so promising some companies tried to use unaltered ancient alloy formulas-Just pure gold, copper and silver without any additives. While these alloys avoided the pitfalls of silicon sticking in the newer “bottom pour” electric casting machinery, they were not ‘tuned’ for the new machines. As it turned out certain gas reactions with the investment plaster also prevented the best possible results. This taught us that additives do help a great deal. They always will when applied correctly.
Today’s demanding market sees casters using all kinds of equipment. On one hand we have casting machines that completely isolate the metal from air with exotic gases or a vacuum. Those use resistance or induction for heat. The method varies, but the one thing in common is that air need not get to our gold anywhere near molten temperatures. So, we tune alloys accordingly.
Alloys and casting harmonies-It’s an orchestra like any other. Nobody can be out of tune!
Your alloy maker’s job is to match your alloy to your process. Not just casting, stamping or fabricating, but one must precisely see what equipment is being used. You might use alloys adjusted for “pressure over vacuum” vertical casting systems. Each kind calls for certain alloy tuning.
Karat your gold before casting.
Be sure to blend your gold and alloy, pour it into shot, and only then re-melt for casting. This assure consistent color and karat through the tree. This prevents several potential problems with just a small amount of extra effort
Learn to raise and lower karat in your trees and sprue metal.
Many alloys can be useful in two karats or more. Consider using 1oky sprues by up karating with gold, using some fresh 14kt and casting on less gold overall.
Your Alloy maker as your Metallurgical Guide
Metallurgy is a complex and often counterintuitive science that frankly only a practicing metallurgist can love. Let that person be your guide to enhanced quality in your production. His or her knowledge can save you hours of work and thousands of dollars.
Have confidence in metallurgy, never allow alloy oddities to confuse you.
Today’s most modern alloys are 99% just like the alloys we always could depend on. Gold, silver, copper etc. However, that last 1% makes all the difference in reliable casting. As we use ancient precious metals, we can now use up to the minute technology in that crucial; last, 1% or the gold. That last one percent can contain many additives that make an important difference. These differences include grain structure, ease of filling in small items, hardness, and trapping nickel into the alloy so tightly as to pass certain restrictions abroad.
In the best scenario, your alloy is custom tuned. Not merely adjusted for your equipment but also adjusted further, for whatever you are particular line calls for. Tiny items can be cast with alloys that are far from ideal in larger items like mans rings. More or less hardness as needed. Color tuning for that special look. All of this is very likely in the modern alloy market. Your alloy maker can give your casting gold exactly the tune up you need. Make the call. Send the email. You will be glad you did.
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