I believe everyone agrees that imitation constitutes, in a certain sense, a certificate of esteem.
As we well know, the rarer, more precious and expensive an object is, the more it is imitated.
The world of precious stones is one of those fields where, throughout history, more capital and energy have been poured into obtaining imitations as similar as possible to the original. 
Diamond naturally occupies the very top places in this special ranking.
Benvenuto Cellini (1500-1571) already taught how to modify glass to give it the appearance of a diamond but it was only in the 18th century that a real race began to look for ever better imitations of this fantastic mineral with unique characteristics.
It was then that the Venetian glassmakers realized that by adding lead oxide to the glass they increased its shine and obtained from this simple and not very bright material a greater optical dispersion of light, effectively creating the first imitations of Diamond.
Then came the metal coverings of the lower part of the diamond-shaped glass, the pavilion, to better trap the light and even today, by replacing the metal with a thin layer of plastic material called foilback, they are produced (to be honest, not very credible) imitations of the Diamond in plastic or glass.

They are the Rhinestones which take their name from the Rhine valley from which the colorless quartz once came which, when suitably coated, also constituted for a long time an unlikely imitation of Diamond.
Artificial glass, however, reached its most successful period as an imitation of diamond in the mid-18th century when the Austrian Joseph Strasser patented a lead-based glass, coated in its lower part with mirror, which had the peculiarity of possess a relatively high refractive index. Even today this glass is widely marketed under the name of strass. 
In the twentieth century, a series of stones were synthesized and then used as imitations of diamond.
In the 1920s, thanks to the Verneuil or flame fusion method, colorless synthetic spinel and colorless synthetic corundum were synthesized. 
Both of these two easily distinguishable from Diamond.
Synthetic spinel because it has a low light dispersion (less than half that of Diamond), a typical anomalous birefringence, low brightness and characteristic gas bubbles which, observed under the microscope, denote its synthetic origin.
Colorless synthetic corundum has greater hardness but an even lower dispersion than spinel. Therefore the first indication is obtained with the naked eye and in this case any doubts can be removed with the use of the refractometer as these two stones have an index that is quite close to each other but very different from that of the Diamond.

Despite everything, due to the lack of valid alternatives, they have been used for hundreds of years as imitations of Diamond, having, as we were saying, a refractive index very distant from that of Diamond (with the consequence of much less brilliance and fire) but They have a fair hardness and therefore a longer life compared to previous imitations and, what is always important, a very low cost.
In the fifties, again with the flame fusion method and always with the aim of creating more credible imitations of diamond, Synthetic Rutile was produced and a few years later Strontium Titanate, the latter marketed under the name of "Fabulite". Today these two imitations are rather out of use but from time to time we still find them.
Unlike in the other two previous cases, the high dispersion of Diamond, in the case of rutile and Fabulite constitutes a distinctive defect element. 
In fact, the dispersion of light in diamond is very high but in Strontium Titanate and especially in Synthetic Rutile it is very high so much so as to create, especially in the latter, an evident iridescence effect visible even to the naked eye. 
Even at first glance, compared to the Diamond, you will notice something wrong. A certain, so to speak, excess that will give you a consequent feeling of "false".
Furthermore, both of these imitations have a very low hardness, so much so that they almost always appear with damaged corners and edges and that, even if they are not, because they are never used or set, they will always appear, so to speak, "softer" than how much they are not in the Diamond.

Their specific weight (as in almost all imitations, excluding Moissanite) is much higher than that of Diamond. The difference, if they are loose and not assembled, can be detected with a hydrostatic scale but also in a much simpler way.
Especially in the case of "round brilliant" cut diamonds, given the constancy of shapes and proportions (always taking into account a minimum tolerance possibly due to the so-called "hidden weight" desired by the cutter to conserve as much mass as possible) to a certain size of the The average diameter of the belt always corresponds to a certain weight. 
A round cut diamond of which the average diameter of the girdle is 6.5 mm, for example, will always have (apart from cases, as we were saying, of "hidden weight" where however the differences have minimal percentages) the weight of 1 carat. It is therefore sufficient to simply use a caliper and then a scale calibrated in carats to carry out a further separation. 
A few years later, at the end of the 1960s, two artificial products appeared on the market as imitations of Diamond: YAG (Yittrium Aliminum Garnet) and GGG (Gadolinium Gallium Garnet).

YAG immediately became famous because it was used by Cartier for the replica of the almost 70-carat diamond that Richard Burton had given to Liz Taylor. When it comes to gossip.
Both YAG and GGG are easily distinguishable from Diamond. The first, despite having a high hardness (8.5 on the Mohs scale) has low light dispersion, a high specific weight and characteristic gas bubbles inside.
Compared to YAG, GGG is a more credible imitation to the eye because it has a dispersion coefficient very close to that of Diamond and a very similar "focus" but what makes it easily identifiable is its very high specific weight (just under double that of Diamond) and the low hardness which in a short time produces a general damage to the polish and therefore almost always presents itself with a damaged belt, corners and apex and even if it had just left a laboratory the edges of the facets would always present an appearance, like we also said about Fabulite, very "tender".

Both, despite being created in the laboratory and having a crystalline structure similar to that of Garnet (Garnet in English) must be considered artificial and non-synthetic materials as their natural counterpart does not exist (or at least has not yet been discovered).
Until now, as you have undoubtedly noticed, we have always talked about imitations that are distinguishable and separable from Diamond without too many difficulties.
From now on with Cubic Zirconia but above all with the "terrible" Moissanite we are starting to get really serious
End of first part.

Continues…

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