Certification from Reputable laboratory 

Mostly all the points raised each affect the price of the diamond and will be labelled on a reputable certificate such as the GIA certificate shown here. Once you have a copy of the certificate it is easier for you to compare stones like for like from different shops and also from me on the Antwerp market if you wish. It is normal to ask to see the certificate and even take a picture of it as you need to know what your buying. If the Jeweller does not allow this or seems uncomfortable then go elsewhere. 

The certificate will have a report reference number that is registered to that specific diamond. It shows all the categories explained above which you’ll need to know about the stone to compare other with. This gives transparency and comfort of what your buying.

 It is not recommended to buy diamonds of value without such certificates as unfortunately there are some sellers will say that a diamond is better than it actually is. Unless it is stated on a certified reputable laboratory certificate nominated below then only a diamond specialist will be able to truly know without a certificate. Also, some jewellers make their own in-house certificate which means it has not been independent certified by a reputable laboratory and is subject to scrutiny.

Well known laboratories with a good standard of certification are:

1)GIA : Gemmology institute of America being the standard in the market. https://www.gia.edu/gem-lab-service/diamond-grading

2)HRD : https://my.hrdantwerp.com/

3)AGS : https://www.americangemsociety.org/page/verifyadiamond

4)GCAL :http://www.gemfacts.com/

5)IGI : https://igi.org/

Usually smaller diamonds under 0.30 carats weight rarely come with a certificate unless requested as there is a cost to having the stone certified by the laboratory which sellers rarely consider worth unless the value of the stone is deemed high value such as fancy colours.