Stone-In-Place Casting for High-End Jewelry
You will find below a helpful article about the in stone casting process as well as which stones are suitable for stone casting or not and why?
Introduction
Not all types of stones are suited for an in stone place casting method- Diamonds excepted , stone minerals are not good conductors of heat, they can suffer shock during rapid heat or cooling.
Up to 2mm diameter cooling and quenching of the flask after casting,it is the most critical stage for thermal shock to stones, the larger the stone the more care is needed. In order for the stone to remain set in the casting and not be placed under excess stress ,its dimensions should match as closely as possible those of the jewelry piece that has been designed. There will always be slight variations in the size of the stone but by using calibrated stones this variation should be minimized.
As said before not all stones can be used for example Amethysts and citrine change colour when they are exposed to temperatures over 350 degree Celsius ( 662F), even certain widely available stones ( topaz) may lose their color. Peridot does not change colours but it is very sensitive to acids or pickling solutions and these operations will dull its polish.
Setting styles used for standard stone in place casting
Suitable stones : almost all types of transparent, non treated, natural or synthetic gemstones can be used : diamond, ruby, sapphire, emerald,aquamarine,peridot,divine,garnet,zircon,green tourmaline, tanzanite. The exceptions : amethyst and citrine as heat affects their color. Amorphous gemstones such as Lapis Lazuli, malachite and turquoise are also unsuitable. The gemstone has to be good quality as inclusions, cracks or flowed cuts can cause it to break.
Settings style :
Pavé : It is a setting method in which the surface of a jewelry item appears to be covered with tiny diamonds. These same sized tiny diamonds are placed in small holes, generally stones are positioned together in a honeycomb pattern. Like the prong setting, pave setting also has small claws, triangular in shape, which hold the stones low and very close so that they produce a carpet of brilliance across the entire surface of a jewelry item.
Bezel : it is a thin metal strip which is soldered with a head that wraps around a gem to hold it in place. Bezel setting requires a proper balance in all the angles. It provides a very secure grip as well as protects gemstone’s edges, the girolle and the pavilion from scratches and chips.
Channel with round or square stone : Gemstones are settled side by side as their girolles are held in between two parallel tracks on each metal wall. This setting gives the impression of floating toning stones in the jewelry item and produces a maximum amount of light as no metal appears in between the gemstones.Channel setting protects the gemstones exceptionally well as none of the stone’s edges are exposed. And so they are safe from hard knocks or general wear and tear.
Prong or claw : This setting often has 3, 4 or 6 small evenly spaced metal claws or prongs that are bent over the girdle to securely hold the gemstone in a piece of jewelry. These claws and prongs are similar in shape and size and attached to the central base part, known as the head or basket, of a piece of jewelry. These heads or baskets are available in various shapes and sizes depending on the stone's shape and size. Common shapes of heads or baskets used in stone settings include round, emerald cut, princess cut, oval, marquise cut, pear shaped and trilliant cut. Each claw or prong extends upward and outward from the head and arching over the gemstone to form a secure and enduring grip. Prongs with platinum metal are considered very strong as platinum is a very dense and solid metal and its thin wires are sufficient to hold the gemstone securely in its place whereas gold prongs with sufficient alloys also give a strong grip.
Invisible setting : Invisible setting is a new and improved setting method that is considered as one of the most difficult setting methods. In this setting, the stones are positioned in such a manner so that metal is not visible from in-between stones that ultimately show the appearance of an uninterrupted and continuous surface. In this setting, stones are grooved just below the girdle and then those grooved stones are slid onto metal tracks to hold them in place.
This setting is appropriate only for multi-stone arrangements that are usually attached in multiple rows.
Wax Tree Assembling
Before welding the wax with the stones on the tree, carefully check that the stones
are set securely by tapping on the wax. If possible, the wax should be welded to
the tree with stones facing downwards or sideways, not facing upwards. This
prevents the formation of air bubbles beneath the stones. The height of the tree
should not exceed 15cm for quality purposes.
Calculating the Weight of Metal Required for Casting
Formula: (wax tree weight minus stones weight) x gr/cm³ of the metal to cast
To calculate the weight of the metal needed for the cast, it is important to remove
the weight of the stones from the wax.
De-waxing and Flask Burnout Cycle
Before beginning the burnout process, the flask should be steam de-waxed for
about one hour. It is essential to use a furnace that can be set accurately and that
is well oxygenated. It may have a rotating rack and preferably has forced air.
The cylinder burnout cycle should be adapted to the type of stone and alloys used.
The maximum temperature must not exceed:
- 630°C (1166°F) for diamonds and emeralds
- 680°C (1256°F) for other sensitive stones
- 730°C (1346°F) for cubic zirconia or synthetic stones
Cooling the Flask
After casting, the flask must be cooled slowly to prevent the stones from breaking
due to thermal shock. Diamonds are much less susceptible to the effects of rapid
cooling than other stones. Cylinders containing only diamonds can be quenched
in water 20 minutes after casting; flasks containing other stones should be allowed
to cool for one or two hours. A special procedure is required for casting delicate
stones in red gold. Red gold needs to be cooled fairly quickly, or the metal will
become brittle.
Sources https://www.ashidiamonds.com/Education/SettingsAndFinishing/Setting_Methods.aspx#Bezel
The Santa Fe symposium 2004-2008