The tarnishing of Silver and Silver Plate has long been a problem for the jewellery and giftware industries, whether they be manufacturer, wholesaler or retailer: indeed the retailer probably has the biggest problem with his stock on show in windows and show cases. To understand the mechanics of Silver tarnishing it is necessary to return to a little school time chemistry.
In the atmosphere we breathe there are several gasses including oxygen, nitrogen and regrettably sulphide gasses and in particular Hydrogen Sulphide, produced from industrial activity, coal burning and natural producers like volcanoes and hot springs. The Oxygen and the Sulphide gasses readily combine with Silver and Copper to form Oxides and Sulphides, both of these groups of chemicals almost always having a black or dark grey colour. These chemicals are what we see when we talk about 'tarnished silver'.
Like many things, prevention is better than cure and several activities can be undertaken to avoid the problem of poor colour in Silver articles.
Simple things that can make a difference are to try and reduce the amount of contact the Silver has with potential discolouring gasses. Try not to use polythene bags for storage, especially the 'gripper' type as they trap gasses inside and create a greenhouse type environment, which is particularly good at creating tarnish.
If you have to use this method of storage, try and pack the products in a clean dry work area using cotton gloves and use 'acid free tissue' first as this reduces exposure. Check with your packaging material manufacturer that they use low sulphur materials and insist they do so.
On the basis that even the best packaging and display will result in some discolouration you need to look at preventative methods: these fall into two classes i.e. original manufacturing methods and post manufacturing treatments.
Prevention in manufacture consists of using Silver alloys that are designed with resistance to oxidation and involve the use of special additives like Silicon or Germanium. This works well if all factors are controlled, including 100% new metal each time when casting, accurate temperature control in melting, annealing etc. and no metal mixing using Silver from different sources. This can be very difficult to set up, as profits in manufacturing Silver will rarely support such an investment in equipment and management.
Electroplating with 100% silver will also reduce tarnishing levels but it only reduces the rate of discolouration. Rhodium can also be used but the cost is usually prohibitive and the colour of Rhodium is a 'blue-white' and visually different from Silver. In addition subsequent repairs to rhodium plated silver jewellery can be troublesome and expensive.
Given that prevention is difficult to achieve we move on to post manufacture prevention. Three basic systems are practical, polymer/lacquer coatings, immersion processes and electrolytic treatments.
Lacquer/polymer systems are really different methods but both seal the surface of the Silver to exclude gasses in the atmosphere. The upside is they are very strong and effective; the downside is they need very technically competent control, are expensive to set up and are not practical on items that 'move' like chains, earrings, cuff links etc. Several companies have tried this method; most have failed in keeping it working. Spray solvent based lacquers are used on Silver plate but atmospheric control is necessary to reduce rainbow colours being introduced and the same problem with moving items still exists: fire and pollution regulations also make this an expensive option.
Immersion dip treatments consist of using various proprietary solutions and they are quite good at removing oxidation but they tend to leave a 'feel' to the surface and many people report a dulling of the surface of metal and stones and the protective surface produced is fragile and unstable. Dipping in Chromate based chemicals works but is again very fragile and will not resist normal handling.
Electrolytic 'Passivation' of the surface is the best and most practical option for the jewellery and giftware industries. The process creates a passive surface that resists Oxygen and Sulphides by creating a barrier, rather like the anodising of Aluminium used on buildings.
The items to be treated are first cleaned in a special solution to remove traces of often-invisible tarnish, followed by the Passivation stage for 1 to 2 minutes, washing in water and then drying to complete the cycle. Twelve to eighteen months' protection in stock or on display would be usual from this method and even non-abrasive handling will not harm the surface.
With our Silverbrite units Electrolytic Passivation is easily achieved although we can supply Silverbrite units in sizes to suit the individual company. However most retailers choose our model TP25 for its' size and low cost. Operation costs are minimal, typically less than one pence for five ring sized items. The chemicals do not contain cyanides or very toxic substances but, as with any process, normal safety precautions and hygiene are recommended.
Because the Silverbrite electrolytic method does not change the look of the item you may wish to check that the articles have been treated correctly. This can be done very easily with a small 'dip-kit' that will replicate the tarnishing sulphides that caused our problems.
Of course Electrolytic Passivation will not create tarnish-free silver in wear but it will keep your silver stock gleaming. Silver tarnishing is a preventable condition. Take a critical look at your silver stock and then let Silverbrite eliminate that never-ending cleaning problem. |