I always get asked what’s the difference between these two types of silver, when to use them and why. But first, let’s start with what do 925 and 999 mean? These numbers are purity marks stamped into metal, they represent the number of parts out of 1000 of pure metal in the piece. 925 is the purity mark for sterling silver, which is traditionally 92.5% pure silver and 7.5% copper. 999 on the other hand is what’s known as fine silver, 99.9% pure silver.
Ok so when, how and what do you use them for and why?
Sterling silver is a harder metal than fine silver. Which as any of my students would have heard me say, always surprises me. Fine silver is really soft, as is copper… alloy them together and you get a metal that is harder! Yep, I’m easily impressed (and clearly no scientist).
The properties of metal play a large part in deciding which you should use and for what application. I always go back to the teapot, I think it’s a great way to understand the complexities of choosing the right metal for the job. For example, say you make a teapot out of fine silver. You form the shape by hammering it and planishing the surface (thereby work hardening the surface). Once you have completed the shape of the teapot body, you still need to solder on a handle and a spout. By heating the main body of the teapot in order to solder these components on, you anneal it. This returns the fine silver of the teapot to it’s ‘soft’ state. Now unless you were to painstakingly re-planish the surface to work harden it (which may or may not be possible), you’re left with quite a ‘soft’ teapot.
This isn’t ideal in a practical sense.
Any small knocks will dent the teapot. Depending on the shape, you might even be able to squash it with just a firm grip. On the flip side, if you had chosen to make the teapot from sterling silver, even once you have soldered the spout and handle returning the metal to its ‘soft’ state, your teapot would in fact be harder than the fine silver. This is because the sterling silver is a harder metal when in it’s ‘soft’ state than fine silver is.
These properties are often why you see silver jewellery made from sterling rather than fine silver as it is more often than not left in a ‘soft’ state upon completion, due to the fabrication methods. The choice of sterling silver provides more strength and durability for the piece.