Things you should know

Rennie & Co is a British brand with a tradition of making fine pieces of jewellery.  You can trust in our integrity and judgment, however you might find the following topics helpful, just click on any of the headings below for further clarification.

  • 4C's


    Rennie & Co believe that the choice of your diamond should be a personal one.

    Whilst the rise in popularity of the use of the 4Cs has indeed given the customer greater knowledge, it has long been known by Rennie & Co that a diamond should not be judged purely by these criteria.

    Just as one would not presume that two people sharing the same physical characteristics are indistinguishable, it would be unwise to think that the 4Cs negates the obvious fact that every diamond is unique.

    Time and time again our customers testify to the fact that our diamonds sparkle quite unlike any others that they have seen.  Whether you choose to buy online or in-store you can do so with complete confidence.

  • CUT


    The choice here is whether to cut to maximise weight or to maximise beauty.  Commercial pressures often dictate that a higher yield is preferable, particularly when retaining the weight can increase the price exponentially.

    On the other hand to cut a diamond to the exacting precision required by Rennie & Co demands the attention of some of the world’s eminent Diamantaires whose skills are tested to release the brilliance, fire and scintillation hidden within the natural rough.

    To some extent this can be expressed by the cut grade, but this in isolation does not take into account the skill and painstaking attention to detail that sets a fine diamond apart from its contemporaries. 



    The human eye is adept at noticing subtle differences in colour, most of our customers consider “colourless” or “near colourless” diamonds between the grade of D and G to be preferable.  The differences between one colour grade and the next  are barely perceptible especially outside of laboratory conditions.  The slight yellowness that accompanies diamonds lower in colour than G tends to be particularly noticeable outside in natural daylight.  

    For those of a playful nature the allure of fancy coloured diamonds can be irresistible.   Very few such stones are formed in nature, but when they are, they can provide spectacular intense colours such as yellow, chocolate, and pink.



    Every diamond selected by Rennie & Co is natural.   They have not been enhanced or grown in a laboratory.

    Extreme heat and pressure found deep within the earth where diamonds are formed, often lead to tiny internal irregularities or inclusions, whilst these are often visible with the naked eye, Rennie & Co meticulously pick only the very finest stones free of such inclusions.

    As with a person, distinguishing marks can be used to identify one stone from another, however similar they may initially look.



    As an example, a  half carat diamond might have a diameter 5.1mm, where as the diameter of a one carat diamond  (weighing 100% more) will only increase by a further 25%.

    A metric carat is equivalent to 0.20 of a gram.  This in turn is divided into 100 points, so a half carat stone might also be referred to as 50 points or 0.50 carats.  With such an expensive commodity, the scales used to weigh the stones need to be extremely precise and shielded from draughts which can easily upset accuracy.

    The expression of a stone’s weight in carats dates back to ancient times when gems were measured using the weight of a carob seed.



    Naturally occurring, a third of diamonds will be found to be fluorescent to some extent.  One in ten of these stones will have sufficient fluorescence for it to impact on its beauty when being worn in natural daylight, often exhibiting a hazy appearance. 

    The presence of fluorescence is confirmed by examining the diamond under ultra violet light where the stone will emit a bluish glow.

    Rennie & Co do not select diamonds in which fluorescence impacts upon the appearance of the stone in natural daylight.



    Certification or the independent certifying of diamonds by specialist grading laboratories has become common practice within the diamond trade.  The two most highly regarded laboratories are the GIA and the HRD.  Whilst there are many laboratories to choose from, only these two organisations satisfy the standards required by Rennie & Co.  Both are impartial non- profit organisations.

    Certificates will either display a plot of internal characteristics to identify the stone by, or the certificate number will be laser inscribed onto the girdle of the stone. In some cases both will be present.  As assessment can only take place on loose, unset stones certification will normally be carried out long before the diamond is incorporated into a piece of jewellery.

    The cost of certifying a diamond often leads to pieces of jewellery comprising multiple smaller stones being uncertified.  Because Rennie & Co carefully selects each stone in-house we are able to confidently advise customers of the high quality used.



    There are two intended results - To improve the appearance of the clarity, or to effect a colour change.  This can take the form of making the stone less coloured, or whiter, or to change the colour entirely.

    Clarity enhancing techniques usually utilise a laser to drill into a diamond and remove or disguise natural inclusions.  The resulting boreholes can easily be seen under magnification and are often filled to stop the ingress of dirt, over time and often when the ring needs to be cleaned or worked upon the filler can become damaged.  Additionally, fracture filling can be used to dress naturally occurring inclusions.  This treatment is not deemed to be permanent.

    Colour change can be effected by the use of Irradiation, High pressure high temperature (HPHT) treatment or indeed coating of the stone.  

    Irradiation can be used to change colour or to intensify colour.  Its use does not make a diamond more colourless. 

    HPHT treatment can be used to make a stone more colourless, intensify the existing colour or to change the colour of a stone all together.   

    Coating is normally carried out on the back of the stone , so for instance if the stone is a low colour (slightly yellow) by coating the pavilion or girdle blue the colour of the stone would appear to improve, as the blueness is reflected throughout.  Equally if the coating were pink the stone would take on a pink hue. All of the treatments are detectable, their aim being to increase the perceived value and desirability of a diamond.

    This treatment is not deemed to be permanent.

    Rennie & Co use only natural untreated diamonds, by doing so you can be sure that your beautiful diamond will always sparkle and will not degrade over the years ahead. It is endemic in today’s culture to emulate things of great beauty and a fine quality diamond formed within the earth over millions of years is no exception.  This though is missing the point, the reason that natural diamond prices have increased so substantially over the years is because they are indeed a wonder of nature and not of a laboratory. 



    A naturally occurring white precious metal, much rarer than gold and substantially heavier.  The metal is then alloyed to a fineness of 95%, 90%, or 80% in order to affect hardness and durability.  The alloys used will vary dependant on the method of manufacture that follows, but will normally be cobalt, tungsten or copper.

    Our goldsmiths only work with 950 platinum, to achieve a lustrous and durable piece of jewellery


    A naturally occurring yellow precious metal.  The metal is then alloyed to a fineness of normally 75% or 37.5%, again to affect hardness and durability.

    The alloys used will generally be silver and copper.  Fine diamond set jewellery will be made utilising the .higher quality alloy, imparting the piece with a rich yellow colour, less inclined to discolouration.

    Rennie and Co work with only the 18 carat gold, a fineness of 75%.


    Created by mixing gold with white alloys, often silver, palladium and manganese instead of the copper used to achieve yellow gold. The metal will inevitably display a slight yellowness requiring the finished piece of jewellery to be rhodium plated to achieve a white appearance.  This plating will be subject to wear necessitating regular re-polishing and re-plating to be carried out, affecting the longevity of the piece.

    Rennie and Co work with only the 18 carat gold, a fineness of 75%.


    A naturally occurring white metal, normally alloyed to a fineness of 95% or 50%, using mainly ruthenium to do so.  Introduced as a low cost alternative to platinum, it sadly does not possess the same density and therefore lacks the same feeling of presence and desirability when worn.


    Hallmarks are the symbols normally viewed on the inside of precious metal rings and are a legal requirement in Great Britain. These are an assurance as to the purity of metal used and represent one of the oldest forms of consumer protection dating back to 1300.

    Testing and marking are carried out by regional assay offices.  Rennie & Co submit their jewellery to both the London and Birmingham offices.



    Rennie & Co is firmly committed to operating with the upmost integrity, throughout its business. 

    As such they source their polished diamonds only from legitimate sources that subscribe to an international system of certification and warranties known as the Kimberly Process Certification Scheme (KPCS) and The System of Warranties.  The KPCS is a joint government, diamond industry and NGO initiative that imposes significant requirements on its member countries to enable them to certify the origin of their rough diamonds and prevent illicit or “conflict “diamonds from entering legitimate trade.  The System of Warranties is an extension of the Kimberly Process in which members of the diamond trade provide a written guarantee on all invoices that the diamonds are conflict free.  All warranties whether given or received must be audited and reconciled on an annual basis.  The System of Warranties provides assurance that diamonds are from conflict free sources all the way down the supply line to the customer.

    Bullion Supplies

    The bullion used at Rennie & Co is supplied through recognised suppliers of high quality bullion products.

    These companies only procure raw materials through resources that can demonstrate well managed procedures for minimal environmental impact. However, the jewellery sector is the only industry that has for over 4000 years recycled 100% of its products.


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