What colour is Whitby Jet? The English language has many terms to describe the colour black; as black as pitch, black as coal, even as black as Newgate’s Knocker if you are from London, but there is one term reserved to describe the epitome of blackness, and that is the term “Jet Black”. The true blackness of Whitby jet is not fully appreciated until the jet is polished, but when it is, an intense blackness is revealed giving the appearance of looking into a bottomless pool of liquid oil. Many of the jets from other sources worldwide do not exhibit the depth of colour seen in Whitby Jet. The origin of colour in gemstones varies. Sometimes the presence of a certain element within a gemstone can determine the wavelengths of light which are transmitted through it and hence the colour we see with the human eye. In the case of jet, however, almost all the wavelengths of visible light are absorbed by the material itself and as a result, we see black – or the total lack of colour! When jet is highly polished however the lustre achieved is very high and therefore much of the light which hits the surface of the jet is reflected back to our eye. In this case, we see a full-colour mirror reflection, and customers commonly mistake this reflection for a blue or red body colour of the polished jet.