In 1852, the term fluorescence was first used to describe the reaction of UV light to the mineral calcium fluoride, otherwise known as Fluorite.
In gemmological terms, fluorescence is the emission of light from gemstones (and diamonds in particular), when they are exposed to ultraviolet light. Thought to be caused by sub-microscopic defects in the crystal lattice of some gems, this optical effect is caused by the excitation of atoms after exposure to ultraviolet light. Resulting colours can be yellow, white, pink and orange, but most commonly, blue is displayed. Approximately 30–35% of diamonds fluoresce to some degree.
“… diamonds described as strongly… fluorescent were… reported as having better colour appearance…”
In recent times we have noticed many prospective customers insisting that diamonds we present should have no fluorescence. Since most independent diamond grading certificates note the presence and degree of fluorescence, consumers falsely conclude (or are led to believe), that its existence is a negative. They may assume that such stones are cloudy or milky, or that colour and transparency are altered, but in fact this is an extremely rare occurrence.
In 1997, the Gemological Institute of America (GIA) published the results of research into the effect of blue fluorescence on the appearance of diamonds. They concluded that in many cases, particularly if the stones had a slightly tinted body colour, the effect of blue fluorescence had a positive effect by making the diamond appear whiter. After thousands of diamonds were observed by many expert diamond graders, the study concluded that diamonds described as strongly or very strongly fluorescent were, on average, reported as having better colour appearance than less fluorescent stones.
It is important to be aware, (and the GIA states this in their certificates), that fluorescence is a description not a grade. Following on from advice in our last issue, we urge prospective buyers to make use of our practice of presenting a range of stones to allow comparisons, with impartial and expert advice.