To identify synthetic diamonds is no easy task. FTIR microscopy can be used not only to identify diamond imitations as shown in our previous article, but also to estimate whether a diamond has been synthetically produced or thermally improved.
This is exactly what we want to focus on today! And to add another level of difficulty, let’s look at melee-sized diamonds and stones already embedded in jewelry (Figure 1).
With such small and closely spaced stones, identification by standard FTIR spectrometers is difficult. Therefore, FTIR microscopy is a good choice. It works at a higher spatial resolution and measuring points are easier to identify.
And what would be better suited for this than Bruker’s LUMOS II? Thanks to the large working distance of the LUMOS II, it is also possible to identify synthetic diamonds mounted in jewellery that cannot be analyzed with macroscopic methods.
Application example: Jewellery
Figure 1 shows a diamond ring with small stones lying close together. Because of this we performed an FTIR measurement of the individual stones with the LUMOS II FTIR microscope. For this the whole ring was fixed in the sample holder and on the sample stage (Figure 2). Next, the measurement was started and an FT-IR spectrum recorded. From this, we can estimate whether the stone in question is a synthetic, color enhanced or in fact a natural diamond.
Unfortunately, this is not as easy as identifying an imitation. But why is that?
Challenges regarding synthetic diamonds
Until the 1950s, the probability of acquiring a piece of jewelry with synthetic or color enhanced diamonds was relatively low. Nowadays the case is a different one as the techniques used in diamond fraud have become cost efficient and have improved drastically, creating very realistic counterfeits.
As a result, several methods must be used to identify synthetic diamonds and to distinguish them from the real deal. One of these methods is FTIR. It allows to identify different diamond types and that allows some conclusions about the genesis and history of the diamonds. Here is how it works:
Diamonds are not all chemically equal. Apart from carbon which is the main component, nitrogen and boron can occur in the crystal lattice. These impurities can then be detected with FTIR spectroscopy and microscopy and are the backbone of the Diamond type classification.
Nitrogen is the most important impurity, and its presence or absence is therefore the basis of the type classification system. The different types are summed up in Table 1 and the corresponding spectra are shown in Figure 3.
But how does this classification help to identify a synthetic or quality enhanced natural diamond?
Fake or real or color-enhanced?
All above diamond types can be synthesized and color enhanced, however some of them are more prone to fraud than others. In case a diamond is identified as belonging to the rarer types Ib and IIa (account for ~1% and >0.1% of diamonds respectively) chances are high that the stone is not what it pretends to be.
The reason for this is easy to guess. The fact that these diamonds do not occur as frequently in nature means that they are also less often offered on the market and also very expensive. Thus, the probability that the jewelry inherited from grandma contains such rare stones is unfortunately very low. Unless your granny is a royal, of course.
And then, as mentioned before, there are also the color-enhanced stones.
Type IIa and type IaB are of special interest in this case. This is because these diamonds are often grey or brown and thus less valuable. With a so-called HPHT (for high pressure and high temperature) treatment these “ugly ducklings” are turned into popular colorless or pink stones.
Too much info? Here’s the summary.
If an FTIR measurement reveals diamonds of the types IaB, Ib and IIa it is very likely that the stones were either synthetically generated or color enhanced. In the future, the boundaries between synthetic and natural stones will become more and more blurred. While people understandably crave natural diamonds, the synthetic ones are better than their reputation. They have a much better environmental performance than natural stones and are produced under humane conditions.
And in the end, they sparkle just the same.