Have you ever wondered just what the atomic structure of a gold leaf is? How thin is gold leaf? What does its atomic structure look like? How does it even manage to stay intact?
All this and more today, as we explore some of the structural basics of gold leaf, as well as discuss how thin it is in layman’s terms and scientist’s terms.
What is Gold Leaf?
In encyclopedic terms, a gold leaf is a metal leaf constructed by hammering what is deemed to be pure gold into thin sheets through a process called gold beating. The product is usually used for gilding and is available in a wide variety of different purities and shades, though the most commonly used gold foil is still 22-karat yellow gold.
Though gold leaf is technically a metal leaf, the term is rarely used to refer to gold leaf. Instead, you might use the term to refer to thin sheets of metal of any color that does not contain any real gold – i.e. imitation silver leaf, imitation gold leaf, or any other imitation leaf for that matter. Pure gold is 24-karat gold, whereas real yellow gold leaf at 22-karat is around 91.7% pure.
Gilding has been a popular practice for many centuries, whereby gold leaf is applied over a surface to give it a metallic and lustrous shine. Traditional water gilding is the most difficult form of gilding and is, thus, the most highly regarded form of gold leafing. The water gilding method has in fact remained more or less unchanged for centuries upon centuries and is still done by hand, remaining one of the most important gilding techniques.
Besides its uses in architecture and the wider art world, gold leaf is also considered a delicacy in many traditions. Though usually flavorless, edible gold leaf finds use outside of picture frames, where certain cultures lean toward applying gold leaf to foods in an effort to decorate. The idea is more or less to encourage a perception of luxury and high value, despite the fact that it is flavorless.
In Europe, this manifests often in liquors that feature floating pieces of gold leaf. In east Asia, though, you might instead encounter it in a traditional artisan green tea.
So, How Thin is Regular Gold Leaf?
Well, interestingly enough (and following on from the encyclopedic definition above), what is called gold leaf is actually a matter of definition. In fact, it is not always pure solid gold at all. Gold is often alloyed with other metals – i.e. silver or copper – to achieve the desired color. Indeed, the actual color of gold is sometimes deemed undesirable, perhaps not quite gold enough.
As you will no doubt already be aware, the purity of gold and gold leaf is described in terms of karats. This system originated in medieval times with a coin called a mark. This coin weighed 24 carats (based on the system for weighing gems – theoretically equal to the weight of a seed from the coral tree).
Of course, gold being too soft, could not be used exclusively to produce marks – rather, copper and other metals had to be added to produce a harder alloy. Henceforth, the purity of the coin and others after it was then expressed by the proportion of its carat weight that was actually contributed by the gold.
The addition of these kinds of metals for gold leaf, though helpful in some ways, can also encourage the foil to corrode more quickly. Thus, any alloys of this kind would need to be kept indoors, ideally used for gilding items kept indoors.
Pure gold at 24 karats would be so malleable and ductile that there is technically no special difficulty in achieving a thickness (or thinness) of 1 micron by rolling a gold nugget pure and flat. Ordinarily, the relative thickness of gold leaf is defined by gilders in terms of between 4 and 5 millionths of an inch. This can be rendered as 0.1 to 0.125 μm (micrometers).
Digging a Little Deeper
What if we wanted to understand it another way? How many atoms thick is gold leaf when all is said and done?
Well, we know that sheets of gold that are thicker than the above measurements are actually referred to as gold foil. Yes, there is in fact a difference.
Anyhow, gold’s atomic structure has a fact centered in a cubic lattice whose unit cell size is 407.82 pm (otherwise known as 4.08 Å – otherwise known as 4.08 × 10(to the power of -10)m. This is obviously an incredibly small thing to behold – some microscopes cannot even show it to you on a personal level.
The closest atomic separation is 288.4 pm, so the metallic radius of a gold atom is technically half of that, i.e. 144.2 pm. Interestingly enough, the Van Der Waals radius of a gold atom is 166 pm.
If we calculate all of this together we can safely say that the thickness of gold foil would be about 245 unit cells. With two layers per cell in a face-centered cubic lattice, the gold leaf would be around 490 atoms thick assuming each unit cell is aligned along the cardinal directions of the foil (and excusing any imperfection in the lattice).
Depending on the source of the gold leaf (i.e. the quality of the loose leaf and its effect on the gold atoms) this sum is variable by around 25% give or take.
So, there you have it! Hopefully, you are now feeling a little more enlightened with regard to the relative thickness (or thinness) of gold leaf!
FAQs How Thin is Gold Leaf?
This depends on the thickness of the hair, though on average gold leaf will be thinner than most hair, yes. Some hair, though, is incredibly thin. Indeed, some people are substantially less endowed with luscious locks than others. Thus, in the case of such people, these sums might need to be totted up again. Any doubters might like to refer to the actual thickness of gold leaf. Anything whose relative thickness can be measured in terms of its atomic structure should really check itself before it wrecks itself.
Ordinarily, the relative thickness of gold leaf is defined by gilders in terms of between 4 and 5 millionths of an inch. This can be rendered as 0.1 to 0.125 μm (micrometers). However, in the last few years, this record has been broken by some budding scientists and researchers over at the University of Leeds, a city in the north of the UK. This team of researchers has created gold nanosheets with a thickness of only 0.47 nm (approximately 2 atomic layers thick). This is the thinnest example of unsupported gold ever created.
On average, yes, gold leaf is thinner than both paper and human hair. The idea is to beat the gold into a very thin sheet of a thickness of around 0.5 microns. By comparison, copy paper is around 130 microns thick (or thin rather), while human hair averages around 60 microns. Of course, there are exceptions to these rules, such as instances of people having thinner hair, and being less endowed with luscious thick locks than some others.
The standard of thickness for gold leaf does seem to vary among gilders, though around 0.5 microns is a good bet. Much thinner than this and it is likely to break during use. There is a fine line between too thick and too thin. If too thin, then the gold leaf will inevitably break during application. If too thick, though, it could just as easily not properly stick or adhere to the surface it is being applied to.