Soldering Precious Metals
Laser welding is a superior alternative to soldering and is the method we use to produce all the chains we provide. The differences between these two processes are explained below:
With laser welding, energy from a light source is used to fuse two noble metals (silver/gold, platinum etc.) to each other. This results in a finished product of a single alloy. Where a gap needs to be filled, metal is added in the form of a filler wire, made of the same alloy as the item being welded, again resulting in a single alloy. The heat generated in the process of laser welding is focused on a very small area. A virtually undetectable weld with no discolouration of the metal is the result.
Soldering relies on a system where heat is applied to the pieces to be joined and capillary action draws melted solder into the joint. A solder with a lower melting point than the noble metals to be joined is required, thus the filler is not the same alloy as the work piece. Heat travels from the join along the pieces to be soldered and often results in a discolouration of the join area in the form of fire scale where any copper in the alloy is oxidized by the flame. This needs to be chemically or mechanically removed when the join has cooled.
As the heat from soldering (brazing) travels outside of the join area (bombardment zone), it can affect other soldered components (and gemstones) in close proximity in the case of ring claws etc. For his reason, where a number of solder joints occur close together, solders with different melting points (and compositions) are used.
Solder comes in various grades rated by the melting temperature. They are Hard, Medium, Easy and Extra Easy from the highest melting temperature to the lowest. Normally the first joint(s) are done with hard, the next with medium and so forth. Each grade requires a lower temperature than the last, so when soldering with ‘easy’ joints nearby made with medium or hard will not be affected by the lower temperatures.
With laser welding, the highly focused beam is applied for a very short duration which dramatically reduces the area of the bombardment zone compared to that created by soldering. This allows the creation of joins much closer to precious stones, enamels, pearls and so forth, eliminating the need in most cases to remove and replace them.
Precious metals such as gold and sterling silver used in jewellery are alloys containing copper. At the temperatures required for soldering when copper is exposed to oxygen in the air, the result is the formation of cuprous oxide (CuO2) which is reddish in colour and then cupric oxide (CuO) which is black. This is called fire scale or fire stain and must be removed chemically or physically.
In industry, fire scale can be reduced by removing oxygen from the atmosphere where the soldering occurs. The use of fluxes (normally based on boric acid) placed over the join to be soldered helps to prevent oxygen from entering the metals and is common when soldering by hand. Charcoal blocks placed under the item to be soldered can also help by creating CO2 when heated, thus reducing the amount of oxygen around the join.
Argentium Sterling Silver is a modern variation of the 925/75 silver/copper ratio used in traditional sterling silver. It is not by definition Sterling Silver however, as that requires the alloy to be 925/75 as stated above. In argentium, some of the copper is replaced by germanium and the silver percentage is either 935 or 960 parts per thousand. It has a surface that is less susceptible to tarnishing and it also resists fire scale during casting and soldering. The germanium in argentium forms a (self healing) clear oxide coating on the surface of the metal that resists tarnishing.