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18K gold plating

I have found watches and some other stuffs claiming ,18k gold plated and 20K gold plated . How this is done . As far as my chemistry knowledge goes only one metal could be plated at a time, so the plating has to be 24k gold.

I work in Sultanate of Oman as sales executive in a readymix concrete company. This query has nothing to do with my job. This question I have asked to many chemistry professors but haven't got an answer.

Vinayan Veluthedath Puthukkudy
Shanfari Readymix & Crushers LLC - Muscat, Oman
2006

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First of two simultaneous responses --

Alloy gold plating is not unusual.

Neil Bell
Red Sky Plating

Albuquerque, New Mexico

2006

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Second of two simultaneous responses -- 2006

Hello Vinayan,
In decorative gold plating on jewelry a plater can attain a certain "karat" value as plated by adding a percentage of an alloy to the gold solution. Normally gold is supplied as potassium gold cyanide either in a salt form or the gold salts dissolved in hot DI water. This gold is 24k in purity and if added to a non-alloyed bath would plate out a pure gold deposit. If the plater wanted a specific karat or color such as 14,18 or 20 karat, alloying metals are added to the bath. These alloys are usually copper, nickel, cobalt, or silver. Nickel alloys for jewelry have been banned in Europe for some years now. The alloys are normally supplied in a liquid form and can be added to the bath by measuring out a certain amount of milliliters. Some platers prefer to have the alloy(s) mixed with the gold when they order it, for easier replenishment to the plating bath. Hope this answers your question.

Mark Baker
process engineer - Malone, New York

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Dear,

This is just an example.When we are making Tea/Coffee. We have to mix up Milk,Sugar and Tea/Coffee powder in hot water ,then only a cup of Tea /Coffee will be ready. Like that when an electroplater needs 15 or 18 etc. karat gold, he has to use gold salt with other metallic salts like silver salt, copper salt,Cobalt salt(some times in solution form) and when he passes current with different current densities metals will deposit and electroplater will achieve the required karat and color of deposit.

Quadri Farooq
- Oman
June 23, 2009