Cubic Zirconia (CZ) that is now widely spread was first produced in the middle of 60-s in the USSR where this material is called  “Fianite” by the name of Physical Institute of Academy of Science (FIAN – in Russian abbreviated form). In this institute the method of CZ crystals growth and its industrial technology was developed, which is now used by all CZ manufacturers.
          In Russia of those years CZ had been developed for technical application, but in quite a short period of time it gained popularity as a rough material for jewelry.  First lots of white CZ were sold at a price of USD 4 000 per kilogram. At that time colour crystals were obtained as well.
In the late 70-s interest to this production arose in the USA. “Ceres Co.” produced the similar crystals and patented them as Cubic Zirconia.
          CZ is a synthetic material with zirconium dioxide (ZrO2), hafnium dioxide (HfO2) and yttrium oxide (Y2O3) as the main chemical substances. Various luminophore admixtures – lanthanoids and other rare earth elements – are used for colour CZ manufacture. Yttrium oxide stabilizes the crystal lattice in cubic form, hence the name of the material – cubic zirconium.

Main physical properties of CZ are:

-  Hardness – 8-8,5 Moh’s scale

-  Microhardness – 1250-1570 kgf/mm2

-  Density – 5,5-5,9 g/cm3

-  Refractive index – 2,15-2,18

-  Dispersion – 0,059 – 0,062.

          Thus, splendid optical properties, high hardness, very wide colour range of CZ in combination with its relatively low cost – make these crystals the unique synthetic material having no rivals. Till recently all CZ material known in the market have been subdivided into two groups according to complexity of its manufacture (all of it were first produced in Russian Federation):

          White, pink, lavender, golden yellow, purple, champagne, orange, Peridot, red, black. Almost all CZ manufacturers produce these colours.
          From the outset CZ has been used as a brilliant imitator and this makes it the most requested material among jewelry stones including natural ones. In the total volume of CZ rough manufacture the white CZ production amounts to 80-90%. Demand for colour CZ arose later than for white one and with the time flow it has been extruding other synthetic colour materials.

          Hues of blue, emerald green – are produced in Russia and in the USA.
Within last 6 years owing to the Russian researchers’ activity (mostly – employees of “Formica Ltd.”) production technology of the known CZ colours was considerably improved as well as new CZ varieties were created.

          The range of CZ hues has been considerably broadened in the mentioned two groups. For example, instead of simple pink CZ, pink-brown “morganite” or pink-lilac “kunzite” can be offered to a customer. Green CZ is presented by the following hues: “the Ural” emerald green, “Colombian” emerald green, tourmaline color, chromium diopside colour, demantoid colour, tsavorite colour (Fig.1); blue hues are sapphire – tanzanite – blue topaz – aquamarine. Moreover, customers can specify saturation and hue of crystals beforehand.

          Besides the known, above mentioned two groups of colours, our two factories produce absolutely new CZ variants, which can be singled out into separate groups.

 

          It characterized by two differently coloured parts with the clear enough colour verge (see Fig.2). At present the following variants of colour combinations are obtained: blue-beige, white-pink-smoky, blue-green and beige-lavender. It is early to speak of complete imitation of polychrome tourmalines, though apparently it is a matter of time.

          Cabochons produced from such crystals (see Fig.3) imitate corals, nacres, chrysoprase, agate, etc., but they differ in brighter glitter and higher hardness. “Formica Ltd.” also produces Opaque CZ of the following colour: lavender, yellow, tanzanite, violet, pink, olive – green, blue, brown, white and black. This material is good for polishing and is inconvertible for external influence. Semi-transparent opalescent CZ is also offered together with Opaque crystals.

          Majority of jewelers considers Black CZ the most requested, because it imitates black brilliant. However, while set in wax models in the process of jewelry casting black CZ stones become lighter. The reason is in simultaneous influence of temperature and oxidizing medium. Such conditions are destructive for black colour. Recently specialists of “Formica Ltd.” have managed to obtain “special” CZ retaining its black colour under any impact a gemstone could undergo.

          Group includes CZ with the effect of alexandrite, i.e. visible crystal colour changes depending on the illumination. Altogether “Formica Ltd.” produces 12 variants of colour change CZ numbered in accordance with the time of their creation (see Table 1, Fig.4). For example, colour change CZ No.1, illuminated with an incandescent lamp is of Imperial Topaz colour and it is bright green in fluorescent lighting; with the same change of illumination colour change CZ No. 2 changes its colours from violet to light blue; colour change CZ No.5 – from kunzite-pink to almost colorless topaz with bluish hue.
In contrast to natural alexandrite there is no need to take into consideration disposition of optic axis while cutting this material.

          Consumers have been long aware of beige CZ, trade name of this colour is champagne. Disadvantage of such crystals is in their insufficient saturation. Small gems cut even from the darkest crystals are characterized by yellow hue.
          Our company developed new dark brown CZ, imitating brown brilliant. Even the smallest cut gems are characterized by the pronounced brown-chocolate hue. For the convenience of consumers three variants of crystals different in saturation are produced that allows all the size range of cut stones.
          Thus, the above data demonstrates new abilities of CZ as colour jewelry rough material: imitation of natural stones with possibility to select the required colour shade by customers’ request and new variants of CZ refresh the current colour range of gems and undoubtedly broadens designers’ potentiality.
          Jewellery manufacturers are fascinated not only by magnificent glitter, high hardness and endurance of CZ, but also by possibility of original jewel creation in combination with moderate price. We can judge of the jewelers’ growing interest to the new CZ by the orders “Formica Ltd.” receives from its customers. Within the past year the volume of orders is twice as much. We are ready to perform almost every exclusive request for the required imitation.  
          New and unexhausted abilities of CZ allow keeping sure that in the new millennium interest to this material will continue to grow not only from jewelry manufactures but also from consumers.  

Written by Avakyan K. (Ph.D.)

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