Most jewelry is made with not just one metal, but 2 or more melted together in specific proportions to form an alloy. By adding metals like copper, palladium, zinc, and the like, jewelers (and their refiners) have learned to create a rainbow of metal alloys with a wide variety of strengths, working characteristics, melting points, etc.
For instance, sterling silver is the standard metal for silver jewelry. It is an alloy of elemental copper and silver - 92.5% silver and 7.5% copper. The copper increases the strength of the silver, making it stronger and more durable.
Gold is similar in that it is rarely used in its elemental form - pure gold is quite soft and malleable. Remember those TV shows with pirates or cowboys biting down on the gold coin to see if it is real? Pure gold you really can leave a mark in with your teeth.
The most common alloy of gold is 18k yellow gold. The 'k' stands for karat, and tells us the percentage of gold in the alloy. 24 karat = pure gold. 18 karat is 18 parts of 24, so divide 18 by 24 = 75% gold. So, 18k gold is 75% pure gold. What's the rest of it, you ask? To keep the color yellow, usually equal parts copper and silver make up the other 25%.
Is gold always yellow? Technically .... yes! Pure gold is always yellow; other colors of gold are actually gold alloys - created by using different metals in the non-gold part of the alloy. For instance, 14k rose (or red) gold is a common alloy - it contains 58.3% gold (14/24 for you mathy types), with the balance (41.7%) mostly copper. That's why rose gold is coppery colored! It is still a stable, precious, non-reactive metal though, because of the stabilizing properties of the gold. Any gold alloy containing 50% or more gold will be stable and non-reactive, suitable for jewelry and use in mokume gane.
The real question - what is palladium white gold?? This entire post is actually a lead up to answer a question I get all the time - what is palladium white gold?? Is it palladium, or is it gold? By now, you can probably guess it is an alloy of both. I use 14k palladium white gold all the time in my mokume gane because I love its dark gray color and its strength. It is 14k, so we know it has to be 58.3% gold. The balance is mostly palladium, a dark gray precious metal used in jewelry but also in catalytic converters.
Bonus question - Is all white gold made with palladium? No! It is much cheaper to make white gold with nickel, a light gray inexpensive base metal. However nickel white gold is banned in many countries because up to 25% of the population is allergic to it. This (and the color) is why most nickel white gold jewelry is rhodium plated. It's more expensive, but for many reasons palladium white gold is the right choice for mokume gane.
So, with all that information, look at the photo of the billet on this post, and see the 3 colors in a new light - you are looking at 14k palladium white gold (gray), 14k rose gold (red/rose) and sterling silver (white). Does anyone want to guess what percentage of gold the billet contains? (by volume, not by weight - that's another blog post). Hint: half the billet is 14k gold of one color or another. Give it your best guess in the comments below. First two correct answers get a $40 gift certificate good on classes or jewelry!
Update: thanks to those who played! The correct answer was 29.15% . The billet is 50% 14k gold. 14k gold is 58.3% gold, so, 50% of 58.3% = 29.15%
Congratulations to the first two correct answers - Chris L. and Ben B. I'll be emailing your $40 gift certificates. Yay!
Educator, metalsmith, jeweler, maker of custom mokume gane jewelry and wedding rings.