A brief history and current explanation of the process...
Why are there so many different gold baths? Fad and fashion, for the most part. Gold electroplating was originally developed with decoration in mind, and decoration is subject to the whims of those who specify its use.
In the past 148 years, fads and fashions have changed so much that the original Elkington patent has evolved into about 300 different modifications in the United States and about 100 in Europe.
Fashion, being highly changeable, demands only a fraction of the colors and shades at any given time. But most of the baths are asked for in any given 20- or 30-year period.
With the development of the electronics industry in the 1940's and 1950's, platers found a demand for different deposits than had been required for decorative plating. Electronics manufacturers wanted the physical properties of the gold deposits to be modified. They were interested in the conductivity, contact resistance, corrosion resistance, electrical as well as physical wear resistance, and the hardness and purity of the deposits. This has led to the development of over 200 more gold and gold-alloy baths.
The development of hundreds of different gold baths has been paralleled by only about 40 different nickel baths and an equal number of copper baths. The reason for this difference is the price of the metal. The economic laws of gold plating are: use the smallest amount of gold to provide the thickness desired; and plate as fast as possible from a minimum amount of solution, to lower the investment in gold plating facilities.
As the price of an ounce of gold has changed from $20.57 to $35.00 to $850.00 and back to $470.00 (at this writing), the above three economic laws have resulted in great chemical and operating changes in gold plating. The day when a plater could have a single gold solution in the corner of his shop and do any job, competitively, and at a profit, is gone.
Nevertheless, gold plating to meet today's requirements is neither impossible nor overly complicated. At any given time, only certain colors and tints are called for by those who specify decorative gold electroplates, and the electronics industry requires only certain physical properties. Thus only a small number of bath types are really needed at any given time.
In the following sections--Jewelry and Electronic--the golds most widely used now will be described.
Economics and the Trade Practice Rules of the Federal Trade Commission determine how gold is used on jewelry and as decorative finishes. Most costume jewelry that is marked "Gold Flash," or left unmarked, is plated with two to four microinches of gold, over bright nickel. In any season, only 10 to 30 shades at most are in demand in the jewelry-plating centers. Solutions that will economically produce this year's shades are listed in Table I.
TABLE I—Representative Gold "Flash" Baths
|Gold as Potassium
|Nickel as Potassium
Ni Cyanide (oz/gal)
|Copper as Potassium
Cu Cyanide (oz/gal)
|Silver as Potassium
|Current Density (asf)||10-40||10-40||10-35||10-40||--||--||10-40||20-50||10-20||7-10|
*These are commonly used names.
The names do not accurately correspond to the colors—and change with time.
While most decorative deposits are two to four microinches thick, there is a growing demand for deposits with thicknesses of seven to about 30 microinches. These finishes are also plated over bright nickel, although sometimes over silver, and are marked "Gold Electroplated." Gold deposits over 100 microinches thick earn the designation of "Heavy Gold Electroplate." Both of these latter thickness ranges require the use of a higher gold concentration and a lower pH. Generally these plating solutions operate at a much lower temperature than is customary when using flash baths.
Typical baths are listed in Table II. Note: the "N" designation of color refers to a European color standard. Color samples are available, and they make matching and maintaining color much easier.
TABLE II--Typical Acid Gold Color Baths for Heavy Deposits