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REFERENCE
ALL LEVELS | METAL
Depletion gilding. Raising the fine silver. Depletion silvering. All
are used to describe the same process, but one is more accurate
than the others. And here’s why.
To “gild” is to cover something with a thin layer of gold. “De-
pletion gilding” is the removal of other metals from the surface of
a gold object, leaving a richer-gold layer on the surface. Since the
term “gilding” specifically refers to gold, the process of removing
copper from the surface of a silver alloy would more accurately
described as “silvering.” Now, I realize the usage of “depletion
gilding” when referring to silver will continue (even though I wish
it wouldn’t); I just want to make you aware of the distinction.
The same goes for the phrase, “raising the fine silver.” It may
seem that you’ve brought the fine silver in the alloy to the surface,
but you haven’t. You’re not so much elevating the fine silver as
you are getting rid of the copper, leaving the fine silver behind.
The what and why
Depletion silvering is accomplished by repeatedly heating silver
alloys to oxidize the copper at the surface, and then removing the
oxides (cupric oxide, a.k.a. firescale) with acid (pickle). For some
decorative techniques, you need a fine-silver surface that won’t
oxidize. But, because of the softness of fine silver, sterling silver
is often a better choice because it’s stronger. To get the best of
both worlds, you can depletion-silver the sterling silver.
When not to do it
While you might be tempted to use this process to hide firestain
(cuprous oxide), don’t do it! Depletion silvering leaches out
copper oxides from only the outermost atomic layers, leaving a
Depletion Gilding vs.
Depletion Silvering
fragile, porous finish. If you were to sand or even polish the
depleted surface, you’d work through the fine silver and expose
the firestain. Even if you don’t polish it, the fine-silver surface is
now softer than the rest of the alloy, and so is more susceptible to
damage and being rubbed away over time. The best solution is to
prevent firestain in the first place by using a barrier flux, such as
Prip’s or other fire coat.How to
Place a sterling silver (or other silver alloy) object on a soldering
surface. Use a soft, bushy flame to heat the silver evenly to close
to the annealing temperature (dim the lights so you don’t over-
heat the silver). Pay attention to the dark gray copper oxides that
form on the surface [1].NOTE: You can heat the silver only until the surface oxidizes, but
you may need to repeat the process more times. Don’t overheat
the silver, or it may become brittle and less ductile.Allow the silver to cool slightly, quench it in water, and place
it in pickle to remove the oxidization. Rinse the silver in water,
brush it with a soapy brass brush (if desired), and dry it. Repeat
this process many times until the silver no longer oxidizes when
it’s heated (usually 5–15 times). The more times you repeat the
process, the thicker the fine silver will be at the surface. Photo [2]
shows the silver being heated for the third or fourth time. Oxides
still form, but they’re not as prevalent as after the first heating.
The final photo shows what you’re looking for in a properly
depleted surface: pure matte white with no oxidation [3].Here are a few techniques in which depletion silvering
is necessary, if you’re working with sterling silver:- Keum boo
- Reticulation
- Granulation
- Enameling
- Applying gold metal-clay slip or paste
Left to right: Unaltered sterling silver; sterling silver that’s been heated
and oxidized (the gray firescale will be removed with pickle); properly
depletion-silvered sterling silver — it remains matte-white when
heated, and no oxides develop.when to use
Gain a deeper understanding of the technique of
leaching copper from the surface of silver alloys.
by Annie Pennington
Keum boo beads by
Patricia Tschetter;
reticulated cuff by
Karen J. Lauseng.