Making Modern Electrum, an Experiment by Lynn Cobb

PMC Gold spinning element

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.

Began with PMC Gold

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.Untitled-8

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.)Untitled-9

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.

Color comparison. Top is 22 karat PMC Gold only, middle row is gold and 980 alloy, L to R, 3:1; 4:1; 5:1; 6:1. Bottom row is gold and 999 alloy, in same ratios.Image at left: Color comparison. Top is 22 karat PMC Gold only, middle row is gold and 980 alloy, L to R, 3:1; 4:1; 5:1; 6:1. Bottom row is gold and 999 alloy, in same ratios.

Because this initial testing for proof of concept required making tiny pieces in order to try numerous alloys, it would be useful to try making these alloys into larger pieces to see how successful the firing would be. I would also like to try mixing with PMC Flex (imagine the possibilities!) I would also like to test dry construction, adding texture and, conversely, mirror finish. In the past, I have made a tiny castle charm using PMC Gold, one card thick, which had used about 1.5 grams of gold clay. In another piece, I added a gold clay, flat spinning element to a ring.[fig 18] Both beautiful, but even the modest cost savings by using an “electrum” alloy would perhaps make pieces more marketable, while still being “high karat gold.” (the 4 to 1 alloy is 76.4% gold, and could honestly be marketed as 18 karat.) Another avenue for exploration might be mixing an alloy with more copper, creating a strong gold, similar to 14 karat gold. Another option might be to try the 2 gold clay to 1 silver clay alloy. Though my reading suggested more than 33% silver would not have a gold appearance, it could possibly be yet another color. I was surprised that the results of the various alloys seemed to lead to almost identical color, which means that there could be more savings by using the higher silver ratios. (On the other hand, a household member was able to arrange the test pieces in “color” order, which, without knowing, corresponded with the relative amount of silver in each piece.)

The biggest surprise came with the discovery of the greenish color. All of my research previously had been regarding the ancient alloy called electrum. However, after seeing the results, and researching “green gold” I discovered that it, too, is an alloy of silver and gold. Ultimately, having another option with gold color, opens design opportunities.

The Alloys:
Au= gold; Ag= silver; Cu= copper
(labeled with number)  (labeled with number and “+”)
3 parts Au to 1 part Ag 999          3 parts Au to 1 part Ag 980 ( .020 Cu)
4 parts Au to 1 part Ag 999          4 parts Au to 1 part Ag 980 ( .020 Cu)
5 parts Au to 1 part Ag 999          5 parts Au to 1 part Ag 980 ( .020 Cu)
6 parts Au to 1 part Ag 999          6 parts Au to 1 part Ag 980 ( .020 Cu)

unnamedAbout the author: Ms. Cobb designs artisan jewelry of fine silver (.999) metal clay and 22 karat gold metal clay, sometimes set with stones or accented with vitreous enamel. She was named a finalist in the prestigious Saul Bell Design Award competition in 2011. Many of her pieces have been published in jewelry design books, most recently in Showcase 500 Art Necklaces and she has authored several journal articles describing her Flower Series and Castle Series techniques: Second Annual Metal Clay Jewelry issue published by Art Jewelry Magazine; Lapidary Journal Jewelry Artist; Belle Armoire Jewelry; Art Jewelry Magazine.
Ms. Cobb finds inspiration in nature, the sea, abstract interpretation and the myriad architectural forms from antiquity and indigenous cultures. Her love of the works of Georgia O’Keeffe and Judy Chicago, have led her to develop a line of fine silver flowers which are both delicate and bold. Their vibrant sensual forms echo the work of these acclaimed artists and bring the flowers down to a wearable scale.
Ms. Cobb’s work can be found at fine craft fairs in the San Francisco Bay Area as well as online at www.lynncobb.com and  the artisan website Etsy, www.etsy.com/shop/lynncobb

(Photo credit for ring photo.  Ring by Lynn Cobb, photo by George Post.)

6 Responses to “Making Modern Electrum, an Experiment by Lynn Cobb”

  1. Anise Rodriguez

    Lynn, this is a great discovery! Thank you for experimenting and telling us about it. I have found that when polishing some 14kt gold it looks similar to your pictures and not as yellow in color as you would think. I like that you were able to come up with green gold! I’ll pick your brain later. Brilliant!!

Leave a Reply to Cindy miller

Click here to cancel reply.

XHTML: You can use these tags: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>