When rubies are polished, the polisher does not always remove all traces of the stone’s original form. Rubies are frequently cut with a little part from their unpolished form showing someplace on the girdle (middle) or pavilion (bottom). Basically, nowhere that can be seen from the crown, and somewhere that will most likely be obscured in a setting. They are not an inclusion either, since inclusions by definition form inside the stone instead of being a surface feature of the uncut crystal.
While leaving a remnant of the ruby’s original form is not always possible, this done to serve as an indication that it formed naturally. It is also a way for the cutter to show they used the maximum amount of the crystal rough they could.
Sometimes the remnants are more or less flat along the gem’s surface, and sometimes they are slightly indented into the gemstone and concave. These concavities can be polished out at the buyer’s request, with varying losses of carat weight. Furthermore, vendors will only do so on the condition that the specifically requested gem has a final sale.
Usually there is no reason for these natural indentations to be removed if the features are not causing visual or structural problems. For example, in R5771 below the top of the gem looks fine, though there is one of these natural indentations on a small spot in the back. This feature will really not be visible once set.
R5771 | medium | play | left