A spark seems to be inside a gem and disappears when the stone is rotated. A line appears on a facet, but when cleaned, it disappears. Something stays visible from a few positions and looks like it’s inside the gemstone. At first glance, these might look alike during an initial glance. However, they could be dust, a scratch, a reflection, or an actual inclusion. The best way to learn to differentiate between these things is by manipulating the gemstone, light, and focus, not by looking at all the features in the stone at once.
Before looking through the 10x loupe, wipe down your loose specimens with a lint-free cloth. You can use gem tweezers or a stone holder to hold a loose specimen and try to avoid touching the facets with your hands. You can pick up oils and lint that will reflect off the light and confuse you. Look through the gem once, wipe it down, and go back to the same spot. Things that have been stuck on will move around, change shape, or disappear. A true scratch or internal inclusion is attached to the specimen.
One way to practice differentiating between these features is to take one low-quality specimen and inspect one facet with diffused white light. Pick out one feature you can clearly see. Rotate the specimen slowly while maintaining a steady loupe close to your eye. Move the light source without moving the facet. Take note of whether the feature moves across the facet, is on the surface, is inside the surface, or has disappeared. This process of examining the same area multiple times will teach you more than labeling every feature you see.
Because scratches are surface features, they will typically run parallel to a facet and be highlighted by the reflection of light. Depending on the angle of the light, they will appear brighter or darker but always stay in the same spot on the surface. A fracture that goes into the surface can be irregular and may look like it extends into the stone. Adjusting the focus slightly can help: if you focus the loupe to the same level as the surface of the facet, the scratch will be in focus, whereas an inclusion will come into focus below the surface.
Reflections are not stable; when you move the specimen, loupe, or light source, they move, too. Reflections also tend to resemble the edges of facets or the bright light source. If you are new to gemology, you might follow the reflection through the gem and think it is a fracture or an inclusion. When you turn the specimen a little bit, you will see that it either slides along the surface, is stretched out of view, or has disappeared. You can check the same area with diffused and directional lighting to see the difference.
An inclusion stays in the same place within a gemstone, though its appearance may vary depending on the viewing angle. An inclusion can be round or angular, thread-like, dull, shiny, or clustered together with other inclusions. It’s helpful to draw a picture of where they are located relative to the table, girdle, or adjacent facet intersections, so you know where to look for them next time. On the next pass, select one of these features and verify the focus point, whether cleaning has an effect on it, and how it moves when you change the angle of the stone and the light.
