Work Hardening Gold
If you’ve ever cold worked sheet or wire, you know what work hardening is. The further you reduce the metal thickness the harder it gets and less malleable it becomes. If not annealed properly, the metal fractures or becomes too hard to work.
Before annealing gold (or silver), coat the piece with boric acid and alcohol. This flux coating will reduce oxidation and help minimize cleanup. The trick to proper annealing is to bring the metal up to a hot enough temperature long enough to cause annealing. Many times either the metal was not taken to a high enough temperature or the temperature was not held long enough.
The best annealing should be done in a pre-heated furnace for approximately 15 minutes at the recommended temperatures below.
For optimum malleability, Hoover & Strong karat gold alloys will require cooling in one of several different methods:
1. Quench from red heat.
2. Air cool.
3. Quench from black heat. Black heat is a description used for when the work piece no longer glows red (840°F – 930°F)
4. Cool by any method.
There are several choices for quenching medium. All 10K alloys and 14K white should be quenched into water, water plus denatured alcohol or a pickle solution based on sodium bisulfate. Quenching low karat and 14K white alloys into dilute acid solutions may result in stress corrosion. All other alloys may be quenched into the above or dilute acid solutions such as 10% sulfuric acid or 5% nitric acid.
Annealing White Gold
Nickel white alloys should be work hardened completely. Reduce the metal thickness at least 50% before annealing. Otherwise, the heating process will create unequal stress in the metal and encourage fire-cracking. It is often advisable to stress relieve the work piece at 615°F/325°C for a few seconds prior to raising to the full annealing temperature. After annealing allow these alloys to cool to black heat before quenching for maximum malleability.
Annealing Sterling Silver
Before annealing silver, coat the piece with boric acid and alcohol. Silver should be annealed in an oven at 1200° F for 15 minutes — 18ga(.040”). 20 minutes — 8ga. If silver or gold annealing must be done by a torch, a good visual guide is:
Visible Red 900°F Cherry Red 1400° F
Dull Red 1200°F Bright Salmon Red 1600° F
Quench the sterling from black heat. Otherwise, the slow cooling will age-harden the metal.
Heat Treating Sterling Silver
Sterling silver can be hardened by first annealing and then heat treating the metal. Anneal at 1200° F and quench. Place in furnace preheated to 600°F and heat soak the silver for one hour.
Fire Scale — Prevention and Removal
When copper bearing alloys (red, peach, yellow, green golds and sterling silver) are heated in the presence of oxygen, oxides are quickly formed. Cupric Oxide (CuO) is a black layer on the surface of the metal that can usually be dissolved in pickle.
To prevent fire scale, coat the metal in a flux or firecoat to protect from oxidation. The most common flux is to use is Borax powder (sodium borate), which melts at 1367°F/742°C.
Most fire scale is removed by pickling in a sodium bisulfate based solution. A common pickle pot used to hold and heat the solution is a crock pot. The pickle solution works best about 180°F/80°C.
Oxides that are harder to remove, such as those generated with 18K white nickel-containing alloys, can be removed using 5% nitric acid. Fire scale is best removed from silver alloys using a dilute (10%) sulfuric acid solution.
Palladium White Gold
Take the headache out of working with white gold. Our improved 14K and 18K white golds with palladium are superior to white golds alloyed with nickel. The palladium makes this metal far more malleable and easier to work, with 70% reductions in thickness possible between anneals. After annealing allow these alloys to cool to black heat before quenching for maximum malleability. This causes less stress on your tools and emotions.
(See hooverandstrong.com for “Working with Palladium White Gold”). The color of these palladium white gold alloys is the same superior quality as Hoover & Strong nickel-whites.
14K and 18K Yellow Spring Gold
We have developed 14K yellow spring gold which is provided in round wire and sheet form, and 18K yellow spring gold which is available in round wire only. This spring gold is specially formulated so that when it is heat treated, it will harden the alloy in the karat gold. All soldering should be done before heat treating. With this material, you can use a lighter gauge and still maintain the strength and durability of your piece. The gold will
retain its temper which works well for ring bridges, earrings, earring posts, clasps, money clips and lightweight jewelry.
Spring Gold Hardening Instructions
Spring gold anneals like normal gold. To anneal, heat the metal to 1200°F for 10 to 15 minutes in an oven or kiln, or bring to a cherry red color for 30 seconds with a torch. Follow this with a quench. This insures that the alloy will respond to age hardening and develop its characteristic durability. You may apply a fire coat to protect against oxidation. To age- harden, heat the metal for one hour in a furnace at 700° F (370° C). Air cool
the metal before pickling. This process is reversible and any heat treated item can be re-softened or re-heat treated after annealing.
Gold alloys that are best suited to enameling are those that are zinc-free or contain low levels of zinc — less than 2%. Gold alloys containing up to 5% zinc can be successfully enameled provided they are depletion gilded prior to the enamel application.
Alloys recommended for enameling (* denotes zinc-free):
10K Red 18K Yellow 18K Red
10K Green 18K Yellow D 18K Green
14K Green 18K Spring 18K Royal
14K Palladium White* 18K Peach 18K Royal D
14K Red 18K Palladium White* 22K Yellow*
Alloys recommended for enameling with higher zinc contents:
10K Yellow 14K Yellow D 14K Spring Yellow
14K Yellow 14K Yellow D2 14K Peach 14K Royal
©2009 Hoover & Strong, Inc.