Saturday, 19 December 2015

The creation of charms

Horse Charm (chr-2770)-335When you browse our range of solid gold and silver charms you see the finished product of many hours of work and many steps in the creation process.

A new charm begins as an idea in the mind of one of our artisans. It may come from within, or at the request of a customer who is looking for a special item that isn’t otherwise available. He or she will visualise the final design from every angle before putting it to paper to ensure it meets the customer’s expectations.

Making the master

It is rare for a charm to be created in a single step from the final material (silver or gold). Most often the original or ‘master’ charm is created from working with softer and more easily worked compounds. Jeweller’s wax is a common choice to use as it is easily carved and can be heated to make it more malleable. Wax is also quite dense and allows a very smooth surface to be obtained. Fine detail is also easily obtained as can be seen in the texturing found on many of the charms we have for sale.

The wax model is finished to the highest standard possible as it becomes the master from which the copies will be made.

Photo credit: MAURO CATEB via / CC BY

Creating the first charm

A sprue (a wax stem) is added to the wax master so that it can be invested in plaster of Paris. This process involves placing the charm and sprue (stuck to the bottom) inside a small container and filling it with liquid plaster to completely cover the wax. Usually this is placed in an outer container that can have a vacuum applied to remove any air bubbles from the investment (plaster).

When the plaster has dried and hardened, the wax must be removed leaving the shape of the charm and sprue set into the plaster mould. A high temperature oven takes care of this process by evaporating the wax from the plaster. This is called ‘lost wax casting’ and is the most common way of producing multiple charms.

The sprue forms the opening in the plaster where molten silver or gold can be poured to filled the space left by the ‘lost’ wax.

A spring loaded device holds the plaster cast ready for pouring the molten metal and when the catch is released the device spins in a circle. The centrigul force ensures the liquid silver or gold is pushed all the way into the mould and completely fills the space left by the wax. When the metal has cooled the plaster is broken away leaving a perfect copy of the wax carving in metal.

Stage Two

The newly formed silver or gold charm is examined and any final small touch ups are applied. After a final polish to remove any small imperfections the charm is ready to be used to create a rubber or silicon mould for mass production.

A small frame has a layer of rubber laid at the bottom and the charm is placed with the sprue touching one of the walls. Pieces of rubber tightly surround the charm and another layer is applied over the top of the charm. A lid is tightened onto the frame applying pressure to the rubber inside. The frame containing the rubber and the charm is placed into a heater that melts the rubber tightly around the charm creating a re-usable rubber mould. This mould is a block shape with a small hole at the edge where the sprue was positioned.

The mould is cooled and carefully cut around 3 sides to release the charm. The fourth side acts like a hinge helping to realign the mould when it is closed.  Straight cuts are not used, but rather curved cuts. This allows the two faces of the mould to more accurately realign.

Doing it all again

Now that we have a re-usable rubber mould, we can create any number of wax copies. The mould is opened and a small amount of mould release agent is applied. The mould is gently clamped and molten wax is poured in to create a new wax charm. This process is repeated until 10 or 20 wax replicas have been created.

A wax base with a stem provides space for attaching each of the wax copies by the sprues. This looks like a small tree with a charm at the end of each branch.

When the tree is complete with as many charms as needed it is placed in a container and filled with liquid investment as before. This time however we can produce many charms with a single pouring. Again when the plaster has hardened, the investment is placed in an oven that evaporates the wax.

The empty mould is then loaded into the centrifuge and a carefully calculated amount of gold or silver is heated to melting point ready to fill the mould. The metal is poured and the spring is released forcing the molten metal all the way into the spaces left by the lost wax.

As before the plaster is broken away from the tree leaving the charms connected to the tree by their sprues.

Final Steps

The sprue is cut near the charm and the small remaining tag is filed or ground away, leaving the charm. The tree with the majority of the sprues attached can be melted down again for re-use.

Each charm is inspected and any casting marks are removed by hand. The charms have jump rings fitted (and soldered if required) and are placed in a mild acid called a pickle for a few minutes. The charms are then thoroughly rinsed in water and placed in a tumbler. The tumbler is a barrel containing stainless steel shot – pins, balls and saucers. Water and a mild detergent are added to just cover the contents of the tumbler. This is then placed on a set of rotating rollers and left to run for 30 minutes to several hours.

The action of the stainless steel shot constantly hitting the charms is called burnishing. This fully removes any marks caused by casting, hardens the outer surface of the charms and creates a beautiful shine to the metal. The charm is then ready to ship to the customer.



The creation of charms

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