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Firescale Explained

I think it’s important to educate consumers about jewelry. The techniques, the materials and so much more! Without further ado, here’s a quick explanation of firescale.

Heating metal causes copper oxides to rise and mix with the air to create a purple, gray or blue color on the surface of the metal. It happens if the metal contains copper (even gold with a high copper content).

“Copper in my silver?!” you exclaim.

“In my gold?!” you continue to exclaim.

Yep, copper is in there. It’s an alloy. Here’s my blog post about gold. It will help explain the metal alloy thing.

As for sterling silver: sterling silver alloy is made up of 92.5% pure silver and 7.5% copper or other metals.

Sometimes the firescale isn’t that obvious, but there it is nonetheless. It might not be a big deal to some. Maybe it’s barely noticeable, or on the back of a pendant, or inside a ring. Well, if firescale is left on the piece it will oxidize faster than the rest of the piece. It will become more noticeable over time. If the piece has a shiny finish this can be a real problem.

There are steps we metalsmiths take to cut down on firescale and ways to remove it.

  1. Do your best to prevent it in the first place by coating the piece with flux before you begin to solder. Flux coats the metal and can help to keep the copper in the metal from reacting with the oxygen in the air.  But, if the metal is heated past a certain point, firescale can occur. Flux was traditionally made with borax and a few other ingredients. Now you can use a borax mixture or choose from other chemical mixtures.
  2. Reduce the amount of time the metal is hot, and not getting the metal too hot.

If heat control and flux don’t prevent firescale then you have to figure out how to get rid of the it. Your options are:

  1. Pickling your piece after soldering is standard practice and removes some firescale. I use alum as my pickling solution, but there are other chemical solutions used for this.
  2. Embrace it and go with a matte finish or patina finish.
  3. Use an abrasive and basically take off layers of metal until you get beyond the firescale. This can destroy fine detail in the work. If great care isn’t taken, the shape of the piece can be altered (screwed up!).
  4. Plate it. This requires equipment or having a manufacturer do it for you.

There is so much involved in making jewelry! The obvious, is creativity and artistry, but there is math, chemistry and physics too.

Here are some sterling rings sans firescale of course!

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