Dangling a Karat
For AJM Magazine- August 1999
Karating your own gold offers an alternative to stocking large volumes of gold casting grain, saving you money.
By Daniel Ballard
Los Angeles is a rough and tumble market. Labor charges in finished 14k gold jewelry can be less than $1 per gram beyond the cost of the actual per-gram gold content. I once saw a list of prices “offered” to subcontractors for setting that was $.08 per stone. Yes, you read correctly: eight cents per diamond prong set. In our neighborhood, cost cutting is king. As a result, you can count on LA mounting houses using every cost-saving trick they know.
One essential trick is to karat your own gold. Karating means changing the karat of existing gold to another karat. For example, when we add karating alloy to 24k to make 14k we call this “karating down.” You can do your own karating up or down from whatever karat gold you have to whatever karat you need.
Whether you use a torch or an electric melter, karating will save you money and make for better results. One reason for the cost savings is stocking just 24k gold leaves you much more able to precisely match gold inventory to orders. I find it frustrating to have 14k white gold in stock, then receive an order for 18k yellow. If I stock 24k and the right karating alloys, I can make what I need as I need it.
An essential element to making this method work is to get 24k gold from your refiner and karating alloy from a specialist. Most refiners do notmake alloy, although some alloy makers refine. Look for a company that refines, makes karating alloy, and casts product to prove the mix. Speak to the alloy manufacturer, not the reseller. The manufacturer can guide you to the best karating alloys for your exact needs. In fact, alloy makers who also cast and roll out product for sale may be the best possible source of technical support.
Be sure you stock the appropriate karating alloys at all times. Alloy is inexpensive at a buck or three per ounce, especially when compared to most other supplies, particularly gold. Another important facet is how you deal with your refiner. If you take your results back in cash, you pay the refining fee. Then when you spend the money later with your refiner/gold supplier, you’ll pay another fee. (No one sells gold without a profit margin!) The smart way might be to take your refining back as 24k gold, then karat strictly as needed, saving one full level of markup. Another advantage of in-house karating is that when you add gold or alloy to your old tree, you “rejuvenate” your old gold for re-casting. Ideally, of course, we’d never need to re-cast old gold. As someone said to me, when you add new gold to old, “you’re contaminating the new gold, not rejuvenating the old!” That person is obviously better funded than most. In an ideal world, we’d use only new metal, never squabble with family, and already have won the big lotto prize! The reality is that most shops must re-use their old gold to remain competitive. However, as you have seen if you cast, you must add new metal to the mix each cast or the quality really suffers. Here we have a delicate balancing act. Too much new gold and your profit suffers. Too little new gold and the quality suffers, raising recast and repair costs beyond profitability. The prevailing opinion is that 40 percent old gold is an acceptable ratio, although I have seen good (not great) results with far higher old metal ratios. Those of you who have cast gold to death knowwho you are!
In essence, by making and adjusting your karat gold as needed, you reduce refining costs, you work with newer metal, and you purchase less gold over the long haul.
A How-To Karating Guide
By now, I hope I’ve convinced you why a small shop might consider doing its own karating. So, you ask, how do you do it?
First the basics: Be sure to use only gold marked 99.9 percent or 99.99 percent pure for initial karating purposes. Remember, not all gold is created equal for karating purposes! A common misunderstanding: Krugerrand coins are not 24k. They contain 1 troy ounce pure gold, but have copper added for strength and durability. (That’s why they weigh more than a troy ounce!) Careful examination of a Krugerrand coin will note the lack of the imprint “999.”
When you add new gold to old, be certain of the karat of the old gold. (The really smart and careful among you will assay used gold.) If it is too high, or worse, too low, you’ll get an unknown karat out of the final mix. Garbage in means garbage out!
To convert any karat to its decimal equivalent, divide the karat by 24.
For example, 14 divided by 24 = 0.58333. To express as a percentage instead of a decimal, move the decimal point two places to the right:
0.58333 equals 58.333 percent, which is the U.S. standard for 14k gold.
Once you have the decimals, the math goes easier. To increase the karat of the gold, find the raising factor at the intersection of the “karat wanted” and “karat on hand” in Table 2 at the bottom of this article..
Multiply this factor by the weight of the karat gold you’re starting with. This will give you the weight of 24k gold you must add to reach the correct karat.
To reduce the karat, find the reducing factor at the intersection of “karat wanted” and “karat on hand” in Table 3 below. Multiply this factor by the weight of the karat gold you’re starting with. This will give you the weight of the karating alloy you must add to reach the correct lower karat.
For example, let’s presume you have 100 dwt of 14k gold that you want to karat down to 10k. Looking at Table 2, you see the reducing factor for 14k to 10k is 0.40. Multiplying 100 dwt by 0.40 gives you 40 dwt of karating alloy to add to your gold.
100dwt 14k + 40 dwt karating alloy = total weight 140 dwt.
If you multiply 140 dwt by .416 (the amount of gold by weight for 10k, given in Table 1 below), you get 58.33 dwt of 24k gold. Notice that this exactly matches the original gold content in the 100 dwt of 14k.
Do this math on a calculator and verify several times before beginning your melt! Mistakes can be expensive.
Like anything else in our trade, there are different methods to calculate karating metal weights. There are also karating charts available in most jewelers reference books.
Ready to Begin
To prepare grain, or shot, you’ll need the following equipment in addition to your regular casting tools and machinery:
* Extra crucibles to handle the different karats and colors of gold.
* A water barrel to pour the molten gold into. We use a 30 to 55 gallon barrel, since this provides adequate water depth to solidify the molten shot before it hits the bottom of the steel bucket.
* A stainless steel bucket or container to catch all the poured shot inside the water barrel, for easy retrieval.
* A long piece of wire bent into a hook shape to retrieve the steel grain bucket.
At our company, PMWest, we use the following procedure:
Use a hydrogen/oxygen mix with a “rosebud” tipped casting torch and set the pressure on the tank regulators at about 50 lb. psi on both gases. Put the karating alloy and gold grain in a good, clean crucible. That crucible should be reserved for working only that particular karat and color of gold. Too often, if we mix crucibles, we find small beads of metal in the crucible after we cast. A small bead of white gold can cause problems when it gets into yellow gold, and we really don’t want lower karat beads mixed into an 18k cast.
Put the stainless steel bucket in the barrel to catch the gold grain. The bucket should be suspended 12 inches to 18 inches below the water level, as measured from the bottom of the bucket. Watch exactly where the bucket settles. You may not be able to see it while you are pouring your shot, and if you don’t know exactly where the bucket is, you will spill karated gold around the bucket and onto the bottom of the water barrel. You’ll have to retrieve the gold by reaching in — and reaching down to the bottom of a 55 gallon barrel of cold water on a cold morning is no fun at all!
Light your torch, adding minimal oxygen by adjusting the valve on the torch. Bring the temperature up slowly, gradually increasing oxygen pressure so you do not blow any metal out of the crucible. Add minimal flux as needed to ensure a clean melt — just a small pinch! If you add too much flux, some will wind up in your castings, appearing as large, black, sometimes glassy voids.
Keep the flame on the gold at all times to keep oxygen from reaching your gold and causing oxidation. The gold should be a bit hotter than when you cast: karating temperature is normally 100°F above casting temperature.
Stir vigorously with a quartz rod in both directions at least 15 times each way, clockwise and counterclockwise. Be aggressive in stirring the molten metal. Do not use graphite rods! Graphite rods have a way of breaking down slowly, leaving little fragments behind that will cause no end of trouble.
Take the torch and crucible together to the barrel of water. Again, be careful not to allow air to oxidize the gold in the crucible by keeping the torch hovering directly above the crucible. Pour the molten metal slowly through the flame into the water directly over the steel bucket.
Shut down the torch, reach into the barrel, and retrieve your bucket of gold shot. Drain off the excess water, taking care not to spill the grain out as well. If the shot is large, re-melt and pour again more slowly. The grain will, of course, be soaking wet. For our safety, we use a hot plate and Pyrex (heat safe) jar to gently heat the shot and dry all the water out before re-melting for casting. You avoid “poppers” — a.k.a. “caster killers” — this way. Use whatever you have to gently dry the shot — blow dryer, oven, whatever. For drying shot, set the oven at 200°F to 250°F and place the gold in a heat safe container. However you dry your gold, be sure to use gloves or allow the container and the shot to cool before you handle them.
This process is essentially the same if you’re using an electric method of melting, such as resistance or induction. Remember to raise the metal temperature to 100°F above the casting temperature for karating. (Karating temperatures are higher than casting temperatures to ensure a good mixing of the alloying metals.) Then pour into a water barrel as described for the torch method. Many of the commercial casting machines come with graining barrel accessories that eliminate the need for a water barrel. Check with your machine maker to see what’s available for your machine.
Karating and alloying gold is really much easier than casting. There are fewer variables, and once you are clear on the math, you can have confidence in your results. Karating will also help you gain a better understanding of how different karated golds behave.
To be successful with karating, keep these few caveats in mind:
• I don’t want to be repetitious, but I do want you to be! Always triple check your math and weights before putting metals together.
• When in any doubt, get an assay. Assays cost $15 to $25 — very inexpensive compared to the cost of shipping out gold in the wrong karat. Overnight delivery services will get your sample to a qualified assay source in 24 hours, and you can ask the assayer to fax you the result for rapid peace of mind.
• Always take care to minimize the molten gold’s exposure to air. This helps prevent oxidation.
• Keep careful track of your scrap and buttons. Use whatever means work well for you to mark them with their karat and color.
• Be sure to use a clean crucible when you karat. Keep a stock of new crucibles on hand, and replace your crucibles regularly.
• For safety’s sake, always dry your grain before applying the torch! As an additional precaution, begin the melt slowly to prevent grain from “popping” out of the crucible and onto your skin. If you’ve ever burned your hand frying food, you can imagine how much worse molten gold burns!
Always use appropriate safety gear.
Once you’ve mastered karating, you will have the basic skills in place to modify your gold with pure base metals or special karating alloys. For an experienced caster, the confidence this experience provides pays off in the long term. For example, with due care you can even push the color in a desired direction: If you want to make a very small batch of 14k green or rose gold, for instance, you can add the right element (silver or copper) with 24k, and still make use of buttons from previous castings. Complimentary skills make for higher quality at lower cost.
Now there is an ideal we can all agree with!
The following are definitions of terms used in this article: some are also generally used within the refining community.
Karating: The deliberate changing of gold content within a metal from one percentage of gold content to another percentage. Another common but less specific term is “alloying.” Alloying can be the mixing of almost any metals or trace ingredients.
Graining: Pouring molten metal into a water barrel to achieve a granular form. This differs from pouring metal into a mold to create bars for rolling or into a flask for casting.
Grain: The result of graining, this is the form the metal takes after it has been poured into water. Also called “shot.” Karating alloy: A metal with no gold content that is formulated for mixing with gold or gold-containing metal. It is usually a combination of at least two elements, such as copper and silver. Some folks also use “alloy” to refer to gold-containing metals, but I have avoided that use in this article to keep confusion to a minimum. Also called premix, compo, or master alloy.
Rosebud torch: A gas-fueled torch with multiple holes in the tip to spread the heat energy over a melt.
Induction melter: An electric device that uses high or medium frequency radio waves to generate enough heat in the crucible to melt and combine karating alloys and gold.
Resistance melter: An electric device that melts metals with a coiled wire heated to a high temperature by electricity flowing through the wire.
Casting shot: Sometimes simply referred to as “shot.” Another term for grain.
**For more on melting gold, see “Torch Song,” in this section or get the back issue of AJM October, 1997.