Gold plated jewelry

1. The development of gold plating technology
The early history of electrodeposition of precious metals onto lesser metal can be reliably traced back to around 1800. Italian chemist and university professor Luigi Brugnatelli, is considered by many as the first person to utilize gold in the plating process. Brugnatelli was a friend of Allisandro Volta, who had just discovered the chemical principles that would later lead to the development of “voltaic”electrical batteries. Volta’s first practical demonstration of this was called a “Voltaic Pile.” As a result, Brugnatelli’s early work using voltaic electricity enabled him to experiment with various metallic plating solutions. By 1805, he had refined his process enough to plate a fine layer of gold over large silver metals. In a letter to the Belgian Journal of Physics and Chemistry’ later reprinted in Great Britain, Brugnatelli wrote: “I have lately gilt in a complete manner two large silver medals, by bringing them into communication by means of a steel wire, with a negative pole of a voltaic pile, and keeping them one after the other immersed in ammoniuret of gold newly made and well saturated”.

Unfortunately, a falling out with the French Academy of Sciences, the leading scientific body of Europe, prevented any of Brugnatelli’s important work from being published in the scientific journals of his day. His work remained largely unknown outside of Italy, except for a small group of close associates.

From the early 1800′s to about 1845, two main commercial processes for coating objects in gold were utilized. For low costs, immersing an object in a diluted form of gold chloride solution (water gilding) allowed a very thin flash of gold to be deposited onto inexpensive objects. For objects where durability and value were required, a dangerous process utilizing mercury amalgam and gold leaf (fire gilding) was the main technique for achieving a thick, durable gold plate over a surface.

By 1839, scientists in Great Britain and Russia had independently devised metal deposition processes similar to Brugnateli’s, for the copper plating of printing press plates. By 1840, this discovery was adapted and refined by Henry and George Elkington of Birmingham, England for gold and silver plating. Collaborating with partner John Wright, and his innovative formulas for potassium cyanide plating baths, the Elkingtons were able to secure the first viable patents for gold and silver plating.

Struggling at first to commercialize their patented processes, the Elkingtons met stiff resistance from the traditional Sheffield plate manufacturers. Unable to license their patents, they later would set up their own respective factories to produce plated silverware, spectacle frames, gift novelties and numerous other low cost plated items. They were so successful in adapting their processes that they soon dominated the decorative metals industry in their region.

From Great Britain, the plating process for gold and silver quickly spread throughout the rest of Europe and later to the United States. In France, gold plated decorative objects were readily accepted by upper society to display their affluence and fashion sense.

In Russia, large scale gold plating for cathedral domes, icons and religious statues were being successfully completed. plating baths and equipment based on the patents of the Elkingtons were scaled up to accommodate the plating of numerous large scale objects. Eventually the use of old techniques such as mercury amalgam gold gilding and water gilding were largely displaced by the plating process.

As knowledge of electrochemistry broaden and its relationship to the plating process became more widely known, other types of non-decorative metal plating would soon be developed. Plating processes for bright nickel, brass, tin, and zinc were adapted for commercial purposes by the 1850′s. Many of these types of platings were utilized for specific manufacturing and engineering applications. As the industrial age and financial capital expanded form Great Britain to the rest of the world, plating processes would find more usages in the manufacturing of goods and services.

Despite the expansion of plating processes to other industries, no significant scientific developments were discovered until the emergence of the electronics industry in the mid-1940′s. With the exception of some technical improvements to direct current (d.c.) power supplies, the period from 1870 to 1940 was a quiet period, characterized by gradual improvements in manufacturing processes, anodic principles and plating bath formulas.

The late 1940′s witnessed the rediscovery of heavy gold plating for electronic components. By the mid-1950′s, the utilization of new and safer plating baths based on acid formulas, began to displace some of the traditional cyanide based formulas in large scale commercial use

The 1970′s led to numerous regulatory laws for waste water emissions and disposal that set the direction for the plating industry for the next 30 years. Improvements in chemical formulas and technical hardware allowed for the rapid and continuous plating of wire, metal strips, semiconductors and complex metal shapes.

Today, chemical developments and a greater understanding of their underlying electrochemical principles, have led to sophisticated plating bath formulas. Greater control over the working characteristics, layer thickness, and performance of gold plated finishes are being achieved. New chemical developments have enabled greater plating speed, throwing power and high quality reliable plated finishes. The plating of exotic materials such as platinum, ruthenium and osmium are now finding broader usages on electronic connectors, circuit boards and contacts. Many experts believe that the expansion of the telecommunication industry will be increasingly dependent on new and innovative plating technology. The electronics industry and the need to support the expansion of their underlying infrastructure continues to drive improvements worldwide in the plating industry.

Future progress in waveform technologies for d.c. power supplies may lead to even greater achievements for the plating and metal finishing industry. In addition, safer “closed loop” manufacturing processes and waste water recyling will continue to reduce work related exposure to harmful chemicals and waste byproducts.

plating processes for all types of decorative and technical plating applications will continue to find new applications as manufacturing capabilities expand into emerging global markets.

2. How is the thickness of gold plating measured?
The thickness for gold plating jewelry are often expressed in millionths of an inch, microinches, or microns. The table below will help provide a basic translation between these units of measurements.


F.T.Cclassification 


microinches(u.s.inch) 


microns(metric) 


“gold flash(10kt.) 

=

7.0microinches 


.175microns 


“gold electroplate”
=

7.0microinches 


.175microns 


“gold plate”
=

20microinches 


.50microns 

To translate all this into real world plating thicknesses and their relationship to U.S. Gov. F.T.C. regulations, the following table expressed in microns is provided as a point of reference.

gold flash – 10 kt gold with a minimum thickness of .175 microns.

gold electroplate – 14 kt or higher gold layer with a minimum thickness of .175 microns.

gold plate – 14kt or higher gold layer with a minimum thickness of .5 microns.

3. Typically how long can I expect a gold plating to last on my jewelry items?
As a rule the thicker the plating, the longer it will last. When done properly, and with normal usage, gold plated finishes can last about 1 year before replating is required!

4. How to measure gold plating thickness?
For applications where plating thickness is critical it periodically measures plated layers using a process called ” x-ray fluorescence”. This non-destructive method is very precise for measuring the actual metal deposition on an object after plating.

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