It’s no surprise that the largest gold coin in the world is a product of Australia – which happens to be one of the largest producers of gold in the world. With a diameter of 31 inches and a thickness of 4.7 inches, the “Australian Kangaroo One Tonne Gold Coin” was created by the Perth Mint in 2011. The following year, Guinness World Records officially verified it as the largest gold coin in the world – smashing the previous record held by the Royal Canadian Mint’s 100 kg Canadian Maple Leaf bullion coin.
The Perth Mint decided to create the 1 metric ton coin to commemorate the 25th anniversary of their Kangaroo Gold Bullion Coin series. The mint couldn’t use their usual striking process because of the coin’s incredible size. Instead, they used their existing furnaces to melt down 35,700 oz of 99.99% pure gold sourced from Australian mines, which they poured into a graphite mold of the coin’s intended design. Once the gold cooled, all the details were finished by hand. All in all, the coin was in production for 18 months.
The coin went on tour across Europe and Asia in 2014 before returning home to Australia. Today, it is the centerpiece of the Perth Mint’s “Gold Exhibition” where it is showcased in all its golden glory on a revolving platform. Based on gold content alone the coin is worth nearly $40 million USD, according to today’s gold prices.
Prior to the 1880s, aluminum was a precious metal worth more than gold. During those times aluminum was extremely difficult and costly to refine, and all but impossible to accomplish on a mass production scale.
These factors not only made aluminum more valuable than gold – they also contributed to aluminum’s appeal as a prestigious and luxurious metal. In 1855, aluminum bars were a featured attraction at the then world-famous Exposition Universelle de Paris. During his reign as Emperor, Napoleon III of France allegedly owned a collection of aluminum plates and flatware that were strictly reserved for entertaining only the most esteemed guests. In 1884, a capstone made with 100 ounces of pure aluminum was set on the great Washington Monument.
But today, we use aluminum to wrap up old food. What happened? While aluminum was difficult to refine, it’s not a geological rarity, like gold. Aluminum is actually the most abundant element in the earth’s crust and the third-most common element (after oxygen and silicon) on the entire planet. The development of the Hall-Héroult electrolytic process in 1886 completely solved this problem by making aluminum smelting cheap, fast, and easily adaptable to industrial-scale production. This combined with aluminum’s commonality reduced its value and eliminated its precious metal status.
Originally valued at about $1200 per kg in the 1850s, aluminum dropped all the way to $1 per kg by the 1890s. Talk about a market shake up! While the drop in value may have stung the aluminum investors of yore (if there were any), the boon to humanity cannot be understated. Thanks to aluminum, we have power lines, airplanes, food and beverage containers, and so much more. What would Napoleon think of that?
In this latest entry of our series on non-destructive assays, we’ll be covering two tests that start out the same way, but require vastly different equipment. Both assays require a sample that must be scraped away from the test object. Even though this can mark the object, the “damage” is minor and easily repaired.
Acid testingAt MGS, we use acid assays every day to evaluate gold purity so we can pay a fair price for it. First, a sample is collected by scraping the object in question against a touchstone (usually made of basalt, slate, or another dark-colored stone with a fine-grained surface) – leaving a visible streak. By applying different concentrations of nitric acid to the streak and measuring the reaction, we can determine the presence of precious metals and accurately estimate their purity. For example, stronger concentrations of acid will dissolve silver and lower-karat gold, while pure gold and platinum will be unaffected.
While the acid assay is a quick, easy, and accurate method for confirming the presence or absence of precious metals, it doesn’t tell you much else about a sample. For a detailed analysis without damage, you’ll need…
Energy-dispersive X-ray spectroscopy (EDS) A scanning electron microscope with EDS capabilities can measure the chemical and physical characteristics of a sample at the particle level. In principle, EDS is very similar to the X-RF assay we offer our clients. The essential difference is that the X-RF assay exposes a sample to x-rays and measures the fluorescence emitted, while EDS focuses an electron beam on a sample and measures the x-rays emitted. Each element's emission spectrum is unique to its atomic structure, so you can determine the exact composition of a sample by analyzing its emissions. In other words, not only can EDS tell you if a sample contains gold, it can tell you what impurities are also present and in what ratios. For example, the EDS results for a piece of gold jewelry would look something like this:
- 29.6% Copper
- 2.48% Zinc
- 8.17% Silver
- 59.74% Gold
- 100% Total Mass
It’s also worth noting that the size of the sample can be extremely small – even smaller than what an acid assay requires. Unfortunately, the extremely detailed test results are not worth the cost for most people.