Silver Coating

Silver Coating Use Electroplating Method or Silver Plating

There are two method for silver coating on metal surface, first using electroplating or silver plating and second way using paint coating. Silver was one of the first metals to be electroplated using certain basic chemical electroplating, and the electroplating industry was thus founded in the 1840s. A great incentive to its development was the ability thereby to provide an attractive appearance and the hygienic handling of foodstuffs without the expense of making a whole article out of the costly metal. For some decades prior to the introduction of silver plating this difficulty had been overcome by the use of Shefield plate, a composite sheet metal made by rolling silver coating and copper coating together. Tableware and decorative articles were then made from the sandwich in such a way that only the silver was visible, actually this ware just silver coated. Electroplating was able quickly to take over this market and establish itself.

Silver raw material for silver coating can be found as silver plate or silver powder. Silver in powder form have dull color, but silver in metal form have bright color. Silver raw material for silver coating using electroplating method can use plate form, but for paint mixture must use powder form.

Silver Metal

Silver Powder

Silver coating using electroplating method has changed little since it was introduced. The solution is traditionally used at room temperature or only slightly warm, although this limits the permissible current density to between 5 and 10 A/ft2. As however, the silver atom is heavy, this corresponds to a rate of deposition of 0.0008 to 0.0016 in/h. The silver electroplate obtained from the simple double cyanide solution in milky white and Matt, but it is very smooth and soft. It can readily be color buffed or burnished to very high luster. Minor addition to the simple silver plating bath have long been known which limit the grain size of the deposit and produce a lustrous or bright silver coating. These are either organic sulfur compounds, typified by carbon di-sulfide, or small addition of other heavy metals such as lead or antimony. The increase in luster lessen the labor of polishing, but the main advantage is that the bright deposit is harder and more wear resistant.

For house hold and table articles, silver is usually applied to one of the copper alloys and predominantly to nickel silver alloy. Nickel silver is an alloy of copper, zinc and nickel, and is thus essentially a brass, bleached to a yellowish white color by the addition of nickel. A minimum 9% nickel is necessary to eliminate the brassy color, and 12 to 15% gives a white alloy.

Silver Coating Use Paint

We can coat metal surface with silver coat using a reflective bitumen paint, such as Alcolin Silver Coating that is used to protect bitumen membranes and equipment against UV degradation. This paint contain of aluminum pigments which can reflect UV light and enhance the durability of bituminous waterproofing equipment.

Many application of silver coating are using this method even the coating strength of coating is not as using electroplating method but still use because very simple way. Beside have good looking, metal also have longer stand to corrode.

Product Using Silver Coating

Wheel with silver coating

Bolt and Nut

Other related articles:

• Chrome Plating
• Nickel Plating
• Chromium Electroplating

Silver Plating Result

Silver is, of course, a beautiful white and highly reflective metal, which is intrinsically resistance to most corrosive influence, especially to fruit acids and foodstuffs. It is, unfortunately, readily tarnished to a most disfiguring dark-brown or black sulphide by the action of hydrogen sulphide in the air or by sulphur compounds in foodstuffs. This tarnish is superficial and does not involve much depth of silver. Silver is therefore the ideal electroplate for household and tableware, and now that detarnishing dips are available the tarnish question is not serious. Since the basis metal is always intrinsically corrosion resistant and the conditions of exposure are not severe, thin coatings are sufficient on articles not subject to much abrasive wear. For table article such as spoons and forks, however, a much thicker coating in necessary to avoid penetration in use. Most reputable silver platters therefore apply relatively thick coatings in excess of 0.001 in to such articles. However, since silver is an expensive metal the tendency is to express the amount applied by quoting the weight of silver per article or per dozen, which confuses the issue unless the area of electroplate is known.

Some ingenuity is often devoted to shielding articles in the plating bath in such a way that a thicker deposit is preferentially applied to places where most wear is to be expected, such as fork prongs and the backs of spoon bowls. In many case silver and all other metals plated from double cyanide electroplating solutions have very good throwing power i.e. the thickness of plating is better in recesses that might be expected.

Silver plating is now increasingly used for electronic parts and for some bearings where use is made of the high electrical and thermal conductivity of the metal respectively.

Cyanide Solution

The basic formulation for all these baths therefore includes the metal cyanide salt and enough sodium cyanide to form the double salt, together with some excess or free sodium cyanide to assist in dissolution of the metal at the anode. Other salts such as sodium carbonate or nitrate are also often present to increase the electrical conductivity of the solution. At one time potassium cyanide was preferred to sodium, cyanide because of the higher conductivity it conferred, but it is much more expensive, and the conductivity can be increased equally well by using as slightly higher temperature. In some cases it is more convenient to prepare to solution from salts other than the heavy metal cyanide, e.g. in the case of zinc and cadmium, the metal oxide is used with even more cyanide. These react in solution to form the metal cyanide and sodium hydroxide. Some indication formulation are given in the table below.





Cyanide solution are of course poisonous if ingested but they are not absorbed through the skin, nor do they fume. The toxic hazard has thus been found been found by long experiment to be remarkably small. Nevertheless, great care must be taken to avoid cyanides being discharged in the effluents from electroplating plants into sewers or streams, as they are so toxic to animal and fish life, and even to sewage bacteria. The reduction of the cyanide content of waste from plants to a very low level is now a statutory obligation and present problem.

Cyanide solutions are alkaline and can be safely contained in steel tanks, which are cheap. They do not require much chemical control, except for ensuring that a sufficient excess of cyanide is maintained (free cyanide). This can be done by a simple titration or even by observation of the state of anodes. On the other hand, cyanide solution absorb carbon dioxide from the air because of their alkalinity, and form a sodium carbonate.

Other articles"

• Electroplating of Silver, Gold and Copper 
• Silver plating result