Since gold clay is so expensive, might there be a way to combine it with silver clay and still have a finished metal that appeared gold in color, but would be less pure than PMC Gold clay and therefore, a little less expensive?
The ancient Greeks and Romans were aware of such an alloy, which occurred both naturally and man made. They called it “electrum” and used it for coins, jewelry and plating. My reading led me to discover that an alloy of more than about one third silver would result in a metal that appeared silver, that is, no gold color at all. Ancient alloys seemed to be no less than about 20% silver. Therefore, my plan was to combine a variety of gold and silver PMC mixes so that the alloys were in that sweet spot of 20-30% silver, to see what shades of gold would result.
1st problem I encountered: PMC Gold is not pure gold [fig.1]. It is 91.7% gold and 8.3% silver, so, simply combining 2 parts of PMC Gold with 1 part PMC3 would not result in one third silver. In fact, a mix of one third silver and two thirds gold “clays” would result in over 38% silver. Based on the idea that over 33% silver would “look” silver, I rejected this mix. Therefore, by my calculations, I determined that the mixes had to be at least 3 equal parts gold clay to 1 part silver clay which would be 68.8% gold, 31.2% silver; 4 to 1 would be 73.4%/26.6%; 5 to 1 would be 76.4%/23.6%; 6 to 1 would be 78.6%/21.4%. These mixes, if they fired successfully, would save some money, and still might result in beautiful gold color.
I also have learned that some ancient electrum alloys contained about 2% copper. My next calculations determined that since PMC sterling .925 is 7.5% copper and .962 (aka 960) is 3.75% copper, if I combined equal parts of 960 and 999, I could obtain a blend of approximately .980. I did the same ratios as above, but since each “silver” in these second test pieces was 980, they should each be about 2% copper.
Complicating this discussion more is the question of “karat”. One karat is 1/24 or 4.1667% gold (e.g. 24k =99.9% gold; 22k=91.7%; 18k=75%; 14k=58.3%). My alloys would range from a low of 68.7% gold to a high of 78.6% gold. My reading also indicated that the millesimal fineness system is slowly overtaking the karat system for indicating gold purity. This is similar to the system we use to indicate silver purity on a parts per 1000 basis. With gold, for example 18k = .750 or 75% gold.
The next problem was deciding how to measure. I had 3 grams of PMC Gold, graciously donated by PMC Connection. My scale only measures grams or heavier, so using it would not work. My solution was to roll out the clay 2 cards thick (using Cooltools #2 guide) cut disks with a straw, which ensured that the proportions were equal across all of the tests. Low tech, yes, but, if it worked, then this could be a way for any metal clay artist to easily mix alloys. I then quickly hand blended, rolled out the alloys to #3 thickness, set aside to dry, making sure to mark each for gold percentage. I simply rolled the pieces into disks. I did not sand or refine the finish before firing.
Of course, all of this was just the start. My next question: How to fire? At this first level of testing, I decided on using the kiln, 1650F on the 10 minute cycle. As these would be small test pieces, torching might be possible, but not consistent temperature. And, not being sure of the final result, a shorter firing seemed like the place to start. *** I do not have a stainless steel container, nor the carbon for an oxygen free firing, so for these tests, I needed to do open shelf firing. Since 14 karat gold contains a much higher percentage of copper, experiments with carbon firing might be an avenue to pursue in trying to approximate a 14k gold, making sure to consider the melting point of copper. (Image of labelled alloy dots:number alone was blend with 999 silver, number with + was with 980)
Finally, after firing, I brushed and tumbled for an hour. First, all of the pieces came thru the firing without a problem. To my eye, these alloys have a greenish tinge, and, possibly the 980 alloys seem to be slightly grayer. They are definitely less “yellow” than 22 karat PMC Gold. The various alloys appear quite similar to me but, having more than one color of gold offers design options. (Image note: left to right, first one is out of the kiln before being brushed. Second is brushed only; third is after an hour of tumbling and fourth is the reverse side of the tumbled pieces, without the identification numbers.)
The price savings of mixing silver with gold using my alloys may be up to 25% depending on which mix is chosen. Is this worth the hassle and cost? This will depend on how the alloy will be used and marketed. I have considered building a solid piece of this lower percentage gold into a piece of jewelry where it is the centerpiece. Previously, I have used a gold paste, made from thinned out gold clay to accent my work. One of the drawbacks with this is determining the value of the gold used for each piece. By making a clay alloy, you know how much gold you have actually used. ( I used a standard straw to measure the gold and silver, this resulted in a total of 36 disks of gold, in total, for the 8 different alloys from the 3 gram pack of PMC Gold. By dividing the cost of the 3 gram pack by 36, I can determine the cost of my test pieces. There was only a tiny amount of remaining gold clay, set aside for using as paste.) Also, when using paste to add gold to a silver piece, each paste mix might be thinner or thicker than the last, sometimes the result may be brighter or lighter gold, not so easy to precisely predict. By making the clay alloys, the color may be far more consistently predictable even though less yellow.
(Photo credit for ring photo. Ring by Lynn Cobb, photo by George Post.)