Preventing Fire Scale with Fire Coat
Happy Wednesday! Let's talk about a basic process you need to follow at the bench: fire coating your pieces to prevent fire scale.
What is fire scale? This is an unsightly layer of black cupric oxide that forms on the surface of copper-bearing metals when heated (think sterling silver, gold alloys). A stubborn layer of nickel can also form on white gold alloys. This mottled black layer can be very difficult to remove even after pickling your pieces.
So what's to be done? Fire coat that jewelry!
Fire coating is a process in which you apply a protective layer of boric acid solution to the metal before soldering or annealing. It turns into a glass-like covering when heated and prevents the formation of fire scale. Most discoloration should be removed with a quick bath in the pickling solution.
My favorite fire coat is Magic Flame 4-in-1 Soldering Compound. This pretty pink paste packs a punch; it contains boric acid, borax, and sodium fluoborate.
You can use this magic solution 4 ways:
1. Dip: Add magic Flame to denatured alcohol. This makes a fire scale resistant coating. Add as much Magic Flame as you want to get an even heavier coating.
2. Liquid Flux: Add Magic Flame to a small amount of water to create a great Gold and Silver Flux.
3. Paste Flux: Use Magic Flame full strength as a great Paste Flux.
4. Casting Flux: Use Magic Flame full strength for a superior Casting Flux
Like most chemicals in this line of work, use eye protection and work in a well ventilated area. Wash hands after use. My most helpful bit of advice **from experience** is to be cautious if using alcohol near your torch! (I am woman enough to admit to setting a fire coat brush on fire!)
This compound may not be the cheapest, and will probably have a decent shipping charge, but it is worth every penny!