Iridescent patina - The recipe

Iridescent Patina
Copyright May 2003
Katherine Palochak <@kpalchk>

This is the basic recipe for the iridescent patina. This patina is
most effective on highly textured pieces, such as torch texture,
rollerprinted and reticulation. It has a slight color interference
pattern, similar to oil on water. It has a high natural luster,
similar to the nacre on pearls, if done correctly with many repeated
dips in a weak solution. It is durable, the colors remain stable to a
high degree, and very slow (years) to darken or further oxidize.
Further oxidation can be prevented entirely by applying Renaissance
Wax when the patina is dry. It is effective on silver, brass and
copper, to a lesser degree with gold. This makes it an excellent
patina for keum-boo applications, since the 24 kt. gold content
remains bright.

Your metal should be thoroughly clean. Wash, or use an ultrasonic,
to cleanse off surface dirt and oil, then rinse with clean water.
Brass brushing the surface is perfectly acceptable, and provides more
surface tooth. The big secret is the addition of two mordants to
enhance and stabilize the colors. I usually use salt and ammonia. The
recipe I use most frequently is:

1 small piece of liver of sulfur, about 1/4 inch in diameter
2 C. hot water
1 Tbsp. clear household ammonia
1 tsp. salt

Your solution should be a very pale straw yellow color. If the
solution is too strong, the colors will work too fast. Add additional
water if you need it. Iodized salt gives a different effect than
kosher salt, each intensifying certain colors the other doesn’t.

Now you need to set up your dipping station, lined up in a row, so
you can progress from one step to the next, quickly and efficiently.
You need a pot of very hot water and bowl of very, very cold water.
Your dipping station will be lined up in a row, from left to right:
pot of very hot water, hot liver-of-sulfur solution, bowl of very
ice-cold water. First dip your metal into the hot plain water to warm
up the metal. The warmer the metal is, the more intense the effect
and the more quickly the liver-of-sulfur solution works. Then quickly
swish it through the liver-of-sulfur solution, then quickly put it in
the cold water to stop the action. Do not leave the piece in the
liver-of-sulfur solution for any time waiting for the colors to
develop. The color will finish developing in the cold water. Repeat
until you get the colors you want. The color range is predictable.
First yellow, then green, red, blue, purple, and black. You can have
several different colors in one piece by selectively dipping just one
part of the piece.

Caution must be used with pieces that have heat sensitive stones, or
stones which cannot take thermal shock well, such as opals. However,
I’ve been successful, even with delicate stones, by not getting the
metal quite as hot when dipping and working more slowly. I have used
this process with pearls, turquoise, fire agates, malachite,
rhodonite, corundums and beryls, with no ill effect to the stones.
However, I would be reluctant to use the process with say, a heavily
included emerald, simply because the thermal shock could cause the
emerald to fracture.

After you have achieved the colors you want, wipe the metal dry with
a soft cloth. Allow to continue drying for several hours. If you wish
at this point, you can “knock-back” the patina on the high points
with a little rouge on a felt buff, so you have the contrast of the
bright silver against the color. Clean the metal again, and apply a
high quality wax, such as Renaissance Wax, or cabinet-grade lacquer.
Wax will dull down the colors a bit, and lacquer will brighten the
colors a bit. For things that will be subjected to a high degree of
wear, such as bracelets or rings, you may want to incorporate guard
wires during the fabrication of the piece to protect the patina from
abrasion. However, on something like reticulation, where there are
natural hills and valleys, the valleys naturally retain the patina,
while the high points become bright and shiny with abrasion,
providing a very lovely contrast.

Hope you have fun playing!

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Those interested in irridescent and other colourings on metals -
including silver - should try to get hold of A.H. Hiorns,
‘Metal-Colouring and Bronzing’, MacMillan, London, 1892.

This book gives numerous recipes including one for silver where
ammonum sulphide and ammonium chloride are the active ingredients (ie
ammonia + salt + sulpur).

Best wishes
Jack Ogden

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Folks, someone pointed out to me that although I had included salt
and ammonia on the ingredients list, I had not put in what you are to
do with them: Mix the salt and ammonia with the liver-of-sulfur. Boy,
do I feel stupid!!!