At left is a sample of the vast golden treasure recovered from the ship S.S. "Central America", which sank in September 1857 while en route from Panama to New York.  The treasure, valued at more than $100 million, represents the largest find of California Gold Assay Bars ever recorded, plus thousands of United States gold coins, raw nuggets, and gold dust.

Click on the image at left to see an enlarged version.

 Image courtesy of the California Gold Marketing Group

The gold fields of California yielded untold riches during the 1850's in the form of tiny yellow flakes and naturally formed nuggets.  The purity of this gold varied, depending on where it was found and with what other materials it was mixed.  In order to determine the purity of their gold, miners would bring their treasure to one of several private assaying firms where the gold was melted, mixed together, poured into ingots, and then tested for purity.  The ingots would then be stamped with their weight, purity and the assayer's mark.  Like snowflakes, each assay ingot was unique - sizes varied from very small to very large (the largest assay bar found so far was the nearly 80 pound ingot found on the S.S. "Central America").  Once marked, Assay Bars became convenient ways to transport gold and/or to serve as stores of value.

Most Assay Bars were destroyed over the years and converted into other forms, such as coins and jewelry.  Because of their high intrinsic value, plain appearance, and general unavailability, few of the bars were saved by collectors.  Some of the smaller ingots that have been preserved may have circulated as money.

The treasure of the Central America contained Assay Bars from the following five firms: 
   Blake and Company
   Kellogg & Humbert
   Justh and Hunter
   Harris, Marchand & Company
   Henry Henstch

Notes:

Sources and recommended reading:
"Private Gold Coins and Patterns of the United States" by Donald H. Kagin, Ph.D.

The California Gold Marketing Group website