This blog provides commentary on interesting geological events occurring around the world in the context of my own work. This work is, broadly, geological fluid dynamics. The events that I highlight here are those that resonate with my professional life and ideas, and my goal is to interpret them in the context of ideas I've developed in my research. The blog does not represent any particular research agenda. It is written on a personal basis and does not seek to represent the University of Illinois, where I am a professor of geology and physics. Enjoy Geology in Motion! I would be glad to be alerted to geologic events of interest to post here! I hope that this blog can provide current event materials that will make geology come alive.

Banner image is by Ludie Cochrane..

Susan Kieffer can be contacted at s1kieffer at gmail.com

Sunday, December 22, 2013

On the fluid dynamics of gold, as in "gold, incense, and myrrh" this Holiday Season!

Gold leaf temples in Bagan, Myanmar
from http://images.smh.com.au/2012/01/27/2919441/art-Burma-Bagan-Temples-420x0.jpg
OK, so gold (a precious metal), frankinense (aperfume or incense), and myrrh (an oil) were given to Kings and other important persons in biblical times. Why? Gold, perhaps representing kingship; incense symbolizing a priestly role, and myrrh, a symbol of death and embalming.
     Well, let's stick to a more-or-less geological topic here, and look at the unique properties of gold, a substance so soft that it almost qualifies for discussion on this blog of "geology in motion." That is, let's look at how gold leaf is produced. It's a long involved process, involving human labor that has changed little in 5,000 years since artsans in Egypt recognized the ductility and its possibility for use. On this website, is the statement that the amount of gold that would fit inside a tennis ball is enough to cover (gold-leaf covered) the dome of the capital building in Atlanta, Georgia!

(In researching this, I discovered a Wiki article on the "Georgia Gold Rush" that might e of interest to the readers.
The Atlanta Georgia capital. The gold leaf was
added in 1958, with native gold leaf
from nearby Lumpkin  County,
where one of the
first American Gold Rushes occurred
in the 1830's.
Paraphrasing and quoting from here, the basic process is this:
Gold is typically mixed with an alloy such as silver or copper to make a grade of gold described by the "carat" system. Goldbeaters typically make 23 carat gold.
     The gold, along with its added alloy metals, are melted in a furnace, and then poured into a cast to make a bar. This bar is then put through a series of rollers, adjusted repeatedly until the bar becomes a sheet 1/1000 of an inch thick.
     But, this is not the end of the process. The gold is then cut into one-inch squares and beaten on large blocks of marble and granite, and, amazingly, ends up with a sheet that is only 1/2500,000 inch thick.
     Along the way, the gold has been cut into one-inch squares and been beaten by hammers. The first stage is referred to as the "cutch."  In it, about 150 skins (formerly ox intestines, but now, Mylar or parchment) surround the gold to hold it together during the beating. Finding something that can withstand the repeated pounding was a challenge. Blocks of marble and granite are used, sometimes placed onto the top of a tree trunk or set deep into the ground to create resiliency. The beaters spend an hour, using a 15-pound hammer and striking the gold about 70 times per minute, while also rotating and turning over the gold alloy packets to ensure uniformity in the expansion. Then, the beaten gold alloy is carefully removed and put into second packets of skins which are beaten for about there hours.
     At this point, the gold is thin enough that the cutter can simply blow on it to move it. (More details here because I'm skipping some.) Basically, at this point there still remains 3-4 hours of beating with an 8-pound hammer, to get pieces that are 1/250,000 thick. After this process, the result is 3.0x3.3/8 inch squares of leaves in tissue paper books that contain 25 leaves.
     Here's a video that shows parts of the process.
Happy Holidays!


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