An Explanation of Assay Acids

When it comes to precious metal testing, the acid test is the most common method used by jewelers, refiners, and others in the field. A standard acid testing kit comes with four different bottles of acid. A common question we get is “what’s the difference between the acids?”

In truth, the bottles all contain nitric acid. The difference between them is potency. Nitric acid is powerful stuff and it will quickly dissolve other metals that are commonly alloyed with gold. Gold testing kits usually come with four different bottles of acid at different potencies – one each for testing 10k, 14k, 18k, and 22k gold.

To conduct an acid test, the piece of gold in question is scraped against a touchstone. This leaves a visible streak of gold dust on the touchstone. Next, acid is applied to the streak. If the streak dissolves from contact with 10k acid, the sample is not gold. However, if no reaction occurs, then it’s at least 10k. If you apply 14k acid to the same streak and it dissolves, then the gold in question is between 10k and 14k. If no reaction occurs, then the gold is at least 14k pure or greater. The potency of the acid is increased until the correct karat level of the gold sample can be determined. Twenty-four karat gold will be completely unaffected by nitric acid – it can only be dissolved by aqua regia (a mixture of concentrated nitric acid and hydrochloric acid).

Because there are only four levels of acid potency, the standard acid test is not ultra-accurate. However, it is a great test for small batches of scrap jewelry. If you bring gold for an acid test at our storefront in the Diamond District, we can pay you up to 98.5% of the gold’s value. Don’t hesitate to contact us or stop by the storefront if you have questions about any of our gold testing methods.

The World’s Most Expensive Gold Items

On most days at the MGS refinery, we don’t melt down anything spectacular. Although there are some interesting pieces that come through, we haven’t refined items anywhere near as amazing as these. Here are five of the most expensive items in the world that happen to be made of gold.

The Henry Graves Super Complication Watch – in watch making, a complication is a feature other than the display of the hours, minutes, and seconds. The more complications in a watch, the more parts it requires – which in turn makes it more difficult to design, assemble, and repair. In the 1930s, millionaire playboy watch-collector Henry Graves was obsessed with having the world’s most complicated watch. Patek Philippe & Co. delivered the watch in eight years time (three years for development, five years for assembly), which featured 24 complications (including a star chart and perpetual calendar) and 18k gold casing. Only one was ever made.
Price: $11,002,500 at a Sotheby’s auction in 1999

Mitchell and King’s goldRush Rally Wax – in honor of the annual goldRush Rally, Scottish car-care product maker Mitchell and King started offering this car wax that uses premium cosmetic ingredients to give cars a golden shimmer. The bottle it comes in is fine grade titanium coated with 24k gold and encrusted with diamonds and Swarovski crystals.
Price: £65,000

World’s Most Expensive Hookah – luxury design firm Aurentum Switzerland crafted the world’s most expensive hookah by using gold, platinum, silver, diamonds, rubies, and fine crystal glass. The bulk of the hookah’s value comes from its intricate craftsmanship.
Price: $1,000,000

Lio Messi’s Left Foot – world-famous soccer player Lio Messi scored a record setting 91 goals in the 2012 season. To commemorate the occasion, Japanese jeweler Ginza Tanaka crafted a 55-pound solid gold replica of the player’s foot. The foot was available for purchase from March to June 2013 to benefit the Lio Messi Foundation. As part of the hoopla, 100 “mini-feet” made with 100 grams of gold were also on sale for $42,000 each, along with 50 gold-plated footprint molds for $94,500 each.
Price: $5,250,000

How to Turn Concrete into Metal

Metal refining has been around since ancient times, but it’s a science that has yet to be perfected. One could call it a cousin of chemistry – the study of matter. There is a lot we still don’t understand about matter, so both sciences have room for improvement. Case in point: scientists have discovered a way to give concrete metal-like properties.

The process has been likened to alchemy – the old science of transmuting lead into gold. However, the technology used to alter the concrete is far beyond anything an alchemist ever used. Concrete powder is placed in a glass container and heated to 2000 °C by a carbon dioxide laser while being levitated by a stream of inert gas. This levitation keeps the molten concrete from coming into contact with the glass and forming a crystal bond with it. As the concrete cools in the presence of other introduced gases, it’ atomic structure rearranges.

The resulting glass-like material is structured in such a way that free electrons are trapped inside lattices of calcium oxide (the main component of ordinary concrete). With the atomic architecture, the concrete can now conduct electricity just like metal.

Of course, there are limitations. The “metallic” concrete doesn’t conduct electricity nearly as well as gold or silver, so it’s unlikely to replace precious metals in future electronics. But, it still has a lot of potential for other applications.