Split stone, referred to as split stone, refers to jewels and jade that are composed of two or more materials and give people an overall impression.

The combination of gems is not a new technology, it has already appeared in the Roman Empire. Roman jewelers used Venetian pine oil to bond three different colored gems together to make a combined gem. Internationally, the split stone composed of two precious stones is called double stone, and the three stones are called triple stone. Two layers of stones are bonded together by colorless adhesive or welding. Three-layer stones are made by gluing two other gem materials together with colored glue, or gluing three gems together with colorless glue (Figure 4- 1-42).

The purpose of splicing is to make smaller natural gems into larger gems, or to make the color and appearance of gems more beautiful and the surface of gems more wear-resistant and shiny. Another purpose of stitching can also provide a hard base for thin and fragile natural gems, such as stitching opals.

Foil also belongs to a special type of mosaic. It adds an opaque backing material to the back of the gem. Reflective materials such as mirrors (such as silver lining or tin foil) can be used to increase brightness and transparency. Colored materials can also be used to make the gemstone produce color or make the faint starlight effect more obvious. Scribed substrates can also be used to simulate cat's eye effect or starlight effect.

Figure 4- 1-42 Two-layer Stone and Three-layer Stone

Before people invented and made synthetic gemstone materials, split stones used to be popular, and now some kinds of split stones are still common.

(2) Main varieties of cleavage stones

1. Garnet and glass double layer

A double-layered stone made of glass and a garnet. Garnet used in the crown is usually a cheaper red almandine, which only occupies a part of the crown. Its purpose is not to add color, but only to improve durability, or to pass the glass off as garnet. In fact, you can't see the color of thin garnet from above. Garnet and glass can make various colors.

2. Imitation diamond inlay stone

There was once a colorless backing glass that was the most popular imitation of diamonds. It was called "Rhinestone", and its name originally came from the crystal of the Rhine. Although we can't see this kind of thing in the high-end jewelry industry today, we can still see it in fashion jewelry.

Another once popular imitation of diamond is the so-called "beautiful gem". The crown of this gem is colorless synthetic sapphire or colorless synthetic spinel, and the waist or below is artificial strontium titanate. "Beautiful gem" makes full use of the advantages of strong luster and high dispersion of artificial strontium titanate, while artificial sapphire or artificial spinel enhances the hardness of the surface, that is, increases the durability. However, the dispersion of artificial strontium titanate is too strong and the effect is not good; Meanwhile, the artificial strontium titanate has low hardness and poor durability. Now this kind of cleavage stone has been completely replaced by other diamond imitations (such as synthetic cubic zirconia, synthetic moissanite, etc.). ).

3. corundum double-layered stone

Corundum diabase is mainly composed of natural corundum crown and synthetic jadeite pavilion. Generally, the most common type is that the crown is composed of natural dark green or dark blue sapphires, while the pavilion is made of synthetic sapphires or synthetic rubies by flame melting, which is mainly used to imitate darker sapphires or rubies. The second stone crown of corundum can also use light natural sapphire or natural ruby to imitate high-quality sapphire and ruby.

Corundum two-layer stones are mainly mixed-cut, with brilliant cuts in the crown and stepped cuts in the pavilion, which are common in the Asian gem market and pretend to be natural rubies and sapphires.

4. Imitation emerald mosaic

Emerald is difficult to be synthesized by flame melting method, and the cost of flux method and hydrothermal method is high, so emerald mosaic stone has been studied and produced.

One splicing method is a three-layer stone with natural beryl as crown and pavilion and green glue. Be very careful when identifying this three-layered stone, because its refractive index is basically the same as that of emerald.

Another kind of emerald imitation is called "Soude Emerald". In the early days, colorless flowers were used as crowns and pavilions, with green glue in the middle. Now the new "Sude Emerald" uses a layer of green glass instead of green glue, and is bonded with colorless glue. The refractive index of this split stone is still timely, but its density is more than 2.8g/cm3, which may be caused by the lead glass in the middle layer.

Occasionally, you can see a crown or pavilion made of natural beryl and a natural colorless stone used as a pavilion or crown.

Today, the most common emerald mosaic stone is made of colorless synthetic spinel with green glue in the middle, which is called Soudeesur spinelles in France. There is also a similar kind of splitting stone, which uses green glass instead of green glue. This split stone is sometimes made yellow-green, which is used to imitate olivine.

Step 5 split opal

Opal is thin and brittle, so it is of little use alone. Opal can be made into a variety of split stones, the most common of which are opal two-layer stone and opal three-layer stone.

Opal two-layer stone is made by sticking a thin layer of opal on a dark material substrate, which is usually dark chalcedony or black glass. The binder used is usually a dark asphalt substance, which retains some elasticity, thus enhancing the durability of the opal part, and at the same time making the opal colorful and easy to see on a black background (and producing the most valuable black body color). Great care must be taken not to confuse this kind of split stone with natural opal containing opal surrounding rock. This kind of natural matrix with surrounding rock, opal and surrounding rock often present irregular interface, while opal double-layered stone often presents linear joint surface.

The production of Opal three-layer stone is basically the same as Opal two-layer stone, but the difference is that the crown of Opal three-layer stone has a layer of colorless and transparent material, which is adhered to Opal with colorless glue to increase wear resistance. This material is usually crystal, but sometimes glass, synthetic spinel and synthetic sapphire are also used. Although this kind of opal three-layered stone is not difficult to identify, it should be distinguished from synthetic opal and similar three-layered stone made of a rainbow-colored ammonite shell fossil in Canada.

6. Star-like rubies and starlight sapphires inlaid stones

Before the synthesis of starlight sapphire by flame melting and star ruby's invention, people used split stones to imitate natural starlight corundum gemstones.

The most common one is the egg-shaped cut natural starlight hibiscus stone as the top and the mirror as the bottom, or the combination of blue (or red) glass and mirror. In another case, use a blue or red cover, which can not only enhance the starlight effect, but also produce the desired color.

It can also be used to cut artificial corundum into an oval shape with faceted stars at the top and a metal substrate at the bottom, or directly carve patterns on the bottom of artificial corundum and make it of reflective metal.

7. Other split stones

In recent years, the following kinds of complex inlaid gems made of natural and synthetic gems have appeared in the market:

1) Mosaic stone with diamond as crown and colorless synthetic sapphire, synthetic spinel or glass as cabinet. A rare mosaic stone, called a backpack diamond, consists of a flat diamond and a smaller diamond.

2) Mosaic stone composed of three translucent and nearly colorless jadeites: one egg-shaped jadeite is inserted into a hollow round cover jadeite, and the third flat-bottomed jadeite is glued. Green colloidal substances are filled between the dome-shaped jadeite and the egg-shaped jadeite, so that the whole mosaic stone looks like high-quality green jadeite.

3) The hollow oval roof is made of synthetic corundum with fibrous ulexite minerals added, and the base is made of hollow oval synthetic corundum.

4) The top of the oval is made of colorless glass or plastic, and the bottom of the shell is glued to make opal imitation.

5) Other assembly stones used to imitate natural gem-grade crystals. For example, many chopping stones are used to imitate emerald crystals: one is to break natural timely crystals, and then stick the fragments together again with green epoxy resin; Another is to drill a hole in one end of light beryl, and then fill it with a green substance similar to resin to make imitation.

(3) Identification of split stones

The key to identifying split stones is to always keep them in mind and study gems in all directions when identifying them. For faceted gemstones, if possible, it is best to measure the refractive index of crown and pavilion at the same time, which is helpful to distinguish garnet from glass mosaic, beryl and timely mosaic.

1. Identification of garnet and glass bilayer

There are several methods to identify garnet and glass monzonite:

1) Put the garnet and glass stone platforms face down on a piece of white paper, and the red circle effect at the top of garnet can be seen on the paper.

2) Observing the crown or waist with reflected light, we can find the bonding line, and garnet and glass on both sides of the line show different luster, color and hardness differences; The color difference is more obvious in the immersion liquid.

3) By magnifying observation, we can see the needle-like rutile inclusions in the top garnet, the bubbles in the lower glass and the joint surface of the two parts.

4) It is found that the refractive index of garnet is often above 1.76, while that of glass is often between 1.50 ~ 1.55.

5) The "red flag effect" can also be seen on the refractometer, that is, when white light is used to measure the refractive index of the crown, the bottom of the gem image will reflect red light on the faceted ruler.

2. Identification of "Beautiful Gem" diamond imitation

1) Measure the refractive index of synthetic corundum (n = 1.762 ~ 1.770) or synthetic spinel (n= 1.728) at the crown. However, the refractive index of artificial strontium titanate measured in the exhibition hall exceeds the upper limit of refractometer.

2) The crown itself has no obvious dispersion, but it is generally well polished, while the pavilion has strong dispersion and signs of wear, such as poor polishing, scratches and a lot of ribs.

3) Observing the mosaic stone immersed in diiodomethane oil, the crown is low and the pavilion is high.

3. Identification of corundum mosaic

The most common variety is natural ruby as crown and synthetic ruby as pavilion.

1) When observed parallel to the waistline, the color difference between the crown and the pavilion is usually obvious, especially when observed in oil immersion. However, it should be noted that some oil immersion with diiodomethane may cause damage to the cemented layer, so it is necessary to detect and take out the gem as soon as possible.

2) Magnification inspection shows that natural corundum inclusions or flat bands can be seen in the crown, bubbles and arc growth lines can be seen in the pavilion, and flat bubbles can be seen at the junction between the crown and the pavilion. From some angles, you may find the reflected light of the joint surface.

3) Under ultraviolet irradiation, the crown usually has no fluorescence reaction, while the pavilion has red fluorescence.

4. Three-layer stone identification of emeralds and other transparent gems

1) adopts oil immersion technology, and it is easy to identify when observed in the direction parallel to the waist surface. Because you will find that the crown and pavilion of the three-layer stone are basically colorless, separated by a flat and thin color layer.

2) The middle ribbon layer can be easily seen by naked eyes when viewed from the direction parallel to the waist, or illuminated from the back with a flashlight. It is also possible that the middle layer is colorless and the crown and pavilion are colored.

3) It can also be found that the contents in the crown are inconsistent with those in the pavilion, and bubbles can be seen in the colored adhesive layer. If the adhesive layer is dry, turtle cracks may be seen.

5. Identification of split opal

If there is no mosaic, the opal two-story stone is easy to identify, and the obvious straight line dividing line can be seen from the side. The opal part presents a color-changing effect, and the base is black. If it is inlaid, especially inlaid, it is difficult to identify the opal two-layer stone. Under the amplification condition, the bubbles contained in the glue between opal and substrate can be found by irradiation with strong light fiber lamp.

The colorless cover can be seen from the side of the opal three-layer stone, and the bubbles and turtle cracks in the glue between the opal and the top cover can be seen by zooming in.

6. Identification of star ruby and starlight sapphire mosaic stones.

At the right time, a starlight substrate imitating starlight ruby and starlight sapphire is easy to identify. From the side parallel to the waistline, you can see the colorless time, sometimes with a little pink, and its color is not affected by the color of the substrate.