Jewelry Manufacturing
by Ms Nandita Ray
Today jewelry is crafted using the traditional method of simple tools and skilled fingers to modern tools and hi tech means. The flow of ideas and the wide range of designs offer this choice. Mass production or made to order is the other factor in choosing a particular method of production. Here is an attempt to bring to the reader a comprehensive idea about jewelry manufacturing.
I am sure many marvel at the beauty
and workmanship of their favorite
piece of jewellery. Many questions
might spring to mind, wondering how
the delicate design was created or
the gem set? What makes the
jewellery strong? Who are these
artisans who wield their art with
such aplomb creating intricate piece
de resistance' with impudence?
Making jewellery is definitely not a
cake walk. Time, technology and
experience have contributed to
strengthening the art of jewellery
manufacturing. When early man began
wearing jewellery fashioned out of
stones, bones or any attractive
material that caught the eye he
hammered, pounded, chiseled and
rubbed to get the required shape and
size. As man matured and ideas grew,
new techniques developed to capture
his imagination in a world of gold,
gems and glitter. From simple discs
to 3D designs were woven with the
help of tools and technology. Skill
still remains the most important
tool and no goldsmith worth his salt
and valued for his craftsmanship
lacks in this department!
Today jewellery is crafted using
the traditional method of simple
tools and skilled fingers to modern
tools and hi tech means. The flow of
ideas and the wide range of designs
offer this choice. Mass production
or made to order is the other factor
in choosing a particular method of
production. Here is an attempt to
bring to the reader a comprehensive
idea about jewellery manufacturing.
Methods used in Jewelry
manufacturing
Methods that are
typically used to make jewellery
from gold and silver and its alloys
are Investment Casting, Die casting,
cuttle fish casting and hand
fabrication. Many jewelers use
CAD/CAM to make jewellery. CAD
computer aided designs and CAM i.e.
computer aided manufacturing to
reproduce a model piece of jewellery
that can be mass produced. Making
jewellery requires knowledge and
expertise in gold smithing,
stonecutting, engraving, mold
making, fabrication, wax carving,
lost wax casting, electroplating,
forging, and polishing. These are
the various steps needed to make
jewellery. The first step in making
a detailed piece is making of a
mold.
Mold
Jewellery making
begins with a mold. A mold is the
exact and perfect replica of the
piece to be made, copied either from
a design or a piece/object. A mold
is shaped around the shape/figure
with the help of casting process.
The casting process involves a
number of steps. There are two
methods of casting, investment
casting or die casting each with its
own advantages.
Investment Casting
Investment Casting is
also called 'lost wax casting' since
the wax is removed by heating in a
kiln or in an autoclave. It is the
earliest metal technique evolved by
mankind and has a history of 4,000
years. Believed to have been
developed by the Mesopotamians, it
remains the most popular process of
making gold (metal) jewellery and
forms the basis of modern investment
casting process. This process
involves dipping a mold into a
ceramic mix. Sometimes new materials
like plastic or polystyrene foam is
used instead of wax. This process
has a number of steps involved.
- A primary model is made in
hard alloy like nickel silver or
just silver.
-
A rubber model is made by
surrounding this primary model,
using sheet rubber in a mold frame.
It is then vulcanized by placing it
in a heated press. On cooling, it is
cut with a scalpel into halves or
more and removing the primary model.
-
This rubber mold is used to make
many copies of the primary model on
wax.
-
Molten wax is then introduced
into the mold cavity by using a wax
injector. On cooling the wax is
removed to get an exact copy of the
primary model in wax.
-
After the desired number of
models has been made the waxes are
arranged in a tree all around a
central feeder in the casting
machine. The central feeder is also
called sprue. The tree placed in a
metal cylinder called flask.
-
A special mixture called
investment plaster is mixed with
water to form a thick liquid and
poured over the tree covering the
wax models. Low vacuum removes air
bubbles and then this is allowed to
cool and harden to form stiff and
sturdy molds.
-
Then the flask is inverted and
placed in a kiln/furnace. The wax is
melted by steam or air to remove all
the wax. The furnace is set in
stages and the maximum temperature
reached is 750 degrees centigrade.
The melting process takes about 12
to 16 hours. This melting down of
the wax is called the 'lost wax
process'.
-
The wax is slowly melted and
drained out completely and all that
is left behind is the investment
plaster mold and this will now be
used to pour the required molten
metal (to be cased) into.
-
The casting process begins by
putting the flask in a casting
machine. The gold metal or its alloy
is melted and then cast into the
investment mold. Then it is allowed
to cool and solidify.
-
After it has cooled down
completely it is immersed into cold
water which breaks off the
investment mold, leaving the casts
in the tree. The casting are cut off
and then made into jewellery pieces
which will then be polished into
completion.
Two types of casting machines are
used the centrifugal casting machine
which is the older technique or the
modern technique of static vacuum
assist machines.
Advantages of investment casting
It is an age old
proven method. It allows the jeweler
flexibility to create complex
designs. The details can be copied
perfectly. The control of color is
better. The finished product can be
highly polished. It results in very
fine surface finish. The
metallurgical properties are also
excellent.
Disadvantages of investment
casting
This
process can result in porosity. Also
the dimensions may not be as
accurate as the die struck method.
This process can and is used for
almost all gold jewellery and
remains a favorite with jewelers
even after 6,000 years later!
Die struck method
Die struck method is a
casting method where the metal to be
cast is forced under pressure into a
mold which is usually made out of
metal. This is a bona fide method of
producing complex shapes. The
earliest recorded history of die
casting by pressure occurred in
1800's.
Using a plunger or compressed air,
molten metal is forced into a
metallic die and the pressure is
maintained until the metal settles
and solidifies.
The pressure reaches 25 tons per
square inch. The intense pressure
causes the atoms in the metal to
move closer together and solidify to
form dies or molds. Using compressed
sheet metal and steel dies mountings
are formed with metal parts
mechanically stamped out.
Each part is matched and fitted into
the correct portion of halved die
and stamped and shaped. A hydraulic
press is used.