Body Tone of Opal

Yesterday on a social network site I was reading a post where a group of people were arguing about the body tone of an opal. How does one know if the opal can be labelled as a Black Opal, Dark Opal or Light Opal? I hope the information below helps.

Body Tone of Opal

Body tone, body of tone, background colour, colour background, body colour or body background all refer to the relative darkness or lightness of the opal, while ignoring its play of colour. This is assessed on a Scale of Body Tone (from N1 to N9).

• Black Opal - is the family of opal which shows a play of colour within or on a black body tone when viewed face-up, and may be designated N1, N2, N3 or N4 on the Scale of Body Tone.

• Dark Opal - is the family of opal which shows a play of colour within or on a dark body tone, when viewed face-up, and may be designated N5 or N6 using the Scale of Body Tone.

• Light Opal - is the family of opal which shows a play of colour within or on a light body tone, when viewed face-up, and may be designated N7, N8, or N9 on the Scale of Body Tone. The N9 category is referred to as white opal.