From:                              A&E Metal Merchants []

Sent:                               Wednesday, 11 April 2012 5:08 PM


Subject:                          April Update





New Things For April




Hollow bangle coils ready to finish in various diameters, tube sizes and shapes.



Solid silver beads are great for soldering on the end to finish off a bangle or neckpiece or for drilling and threading.



Specials For April


Up to 50% off all Gold Filled and Gold Plated Crimps

Only while stocks last

No Backorders

No further discounts apply




Interesting Facts


This month lets talk about fire scale.


What is it


Fire scale is basically the copper that is contained in the sterling silver alloy that is oxidised, it appears as a grey shadow on the silver.


 That in itself is not really much of a problem except that the copper oxide is not just found on the surface of the metal, it penetrates the surface and depending on how bad the firescale is means how deeply into the surface of the metal the copper oxide can be found.


Pickling removes the surface oxide because it etches the copper from the surface of the silver leaving a layer of basically fine silver, but this is only quite a thin layer so once the surface is polished the firescale will return as the surface layer is polished away.


The only real way to remove firescale is to emery or polish off the surface layer until the firescale is no longer visible.


How To Avoid It


The best way to avoid it is to heat your metal in a reduced atmoshere where there is little or no oxygen present. This is the way we anneal silver when we manufacture it. Of course this is not possible in most workshop situations so there are really only two ways to avoid it.


One is to apply a protective layer to the surface of the metal so that the oxygen does not come in contact with the metal, this can be done by using a thin layer of flux over the whole surface of the metal which is then cleaned off afterwards.


The other way is to ensure that you do not heat the metal to the point where firescale occurs. Firescale is basically a function of time and temperature so a lower temperature for a long enough time will still result in firescale, it is a matter of achieving the desired temperature for the shortest time possible.

For example the normal annealing temperature for sterling silver is 650 degrees C. But if you do this in air you will probably get some firescale but if you anneal at 560-570 degress C. then firescale usually does not occur and provided you maintain this temperature for about 10 minutes you will achieve a properly annealed state. So when you are torch annealing you should make sure that you are doing it in a dark area way from any direct light so that you can see what colour the metal is actually going. You have reached the correct annealing temperature when the metal just starts to glow slightly pink. If it is red you have gone too far and will probably get firescale on the surface of your metal.

The same thing applies to soldering, the temperature you can reach is somewhat higher as you are not leaving it there for any length of time and the piece you are soldering is somewhat protected by the flux but you should not overheat the metal, and when solding a large item you should make sure that you do so in a space that is surrounded by fire bricks to hold the heat and keep the whole piece at an elevated temperature.


This is about the right colour for sterling silver when it is at the correct annealing temperature in a dim light torch annealing.

This is too hot and will result in fire scale.


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