How can we differentiate between internal inclusions and cavities , to external imperfections and dirt?
Here are several methods of evaluating the diamonds that will help you see the differences between the clarity characteristics and by that evaluating the clarity and the value of the diamond more accurately.
- The movement system:
When there is an inclusion in the stone, by tilting the stone to one direction, if the inclusion moves in the opposite direction to that which the stone is tilted, then it is an internal inclusion.
If the inclusion moves in the same direction that the stone is tilted, then it is an external imperfection or dirt.
*This system does not apply when the inclusion is in the center of the table.
- The reflection system:
When there is an inclusion in one of the facets, by tilting the stone so that the facet reflects the light, if the inclusion is internal, it will disappear beneath the facet that reflects the light. If the inclusion is external, or dirt, it will be visible in the reflection on the facet (almost appears to float above the facet).
If the inclusion looks like a dark area in the reflected facet it is a cavity.
*This system is useful, especially for the center of the table.
*This system is also useful for finding burnt areas, polish lines and graining lines.
- The “double” system:
Each internal inclusion has a “reflected double” when you look at it from the opposite side of the stone to where it is. If the inclusion is in the crown, by looking through the pavilion it is possible to see the “double” and if the inclusion is in the pavilion, by looking through the crown it is possible to see the “double”.
A double of an internal inclusion always appears above the actual inclusion.
An external imperfection or dirt will normally not have a “double”. If they are doubled, the “double” will appear on the side of the inclusion and not above it. As the internal inclusion is closer or further from the surface of the stone, so the “double” will do the same thing.
A double of an inclusion that touches the surface of the stone will appear to stick or be joined to the inclusion.
The real inclusion is the one that appears closer to you.
***When there is an internal inclusion that shows many doubles through the crown when the stone is balanced, it will downgrade the clarity grade.
Would you like to learn more about diamonds? You can approach the Center of Gemological Studies and register to the most prestige, affluent and respected gemology course in the Israeli Diamond Center.
Hadas Dori Bar Moshe also lectures about diamonds in her lecture: The Secrets of the Diamonds.