Leaching of nickel
Allergy to nickel is the most common form of contact allergy. The symptoms usually occur when you are in contact with objects that emit nickel.The regulations entitled "The Dangerous Substances and Preparations (Nickel) (Safety) Regulations 2005" clearly require that any finding component that pierces the skin may not release more than .2 micrograms of nickel per cubic centimeter per week, and that no other jewelry component release no more than .5 micrograms of nickel per cubic centimeter per week.Information about different coatings
the information is taken from www.sp.se.
Gold only on the surface.
Many objects are plated with gold and the metal under the gold can be silver or base metal. They are often difficult to distinguish from genuine gold work. If you are vigilant, however, you can reveal them quite easily, as they lack control and responsibility stamps
Plating
The thinnest gold coating is called gilding. It is an electrolytic precipitation of gold on metal objects. The gold layer is very thin, usually less than 2 thousandths of a mm *. Not stamped.
Gold doubles
Same method as for gilding but slightly thicker coating. The gold layer is more than 4 thousandths of a mm *. Not stamped. Pure counterfeiters can even have e.g. 18K stamp.
Gold plating
This is the thickest of the gold plating. By mechanical means, thin gold sheet is laid over base metal. Gold layer usually more than 8 thousandths of a mm *. Rarely occurs nowadays. Not stamped.
Gold on silver.
The same type of mechanical coating as plating fixed on silver objects. Gold layer more than 8 thousandths of a mm *. The objects are stamped as silver. * thousands mm = my (µ) = micron.
Other coatings
It also happens that you coat with precious metals other than gold and silver. The most common is a rhodium coating, so-called rhodium plating. It sometimes happens that a so-called "rhodation" turns out to consist of a nickel coating instead. Other precious metal coatings are palladium and platinum. Both rhodium and palladium, like platinum, belong to the group of platinum metals. See further from the periodic table.
Crow gold and cat gold - confusingly similar to real What so many times so convincingly looks like gold, but which then turns out not to be, is a gold-shining variant of the mineral mica, and which has then been popularly (but also mineralogically) used the term "crow gold". Synonymous with this, the word "cat gold" is used. The corresponding silvery type of mica is called "cat silver". However, the corresponding term crow silver is not used.
Source: www-v2.sp.se - Jan-Erik Gardehall