Inclusion

An inclusion is anything inside a gemstone that is not the host crystal: a trapped mineral, a needle of rutile silk, a healed fissure with its fingerprint of tiny cavities, a band of growth zoning. Diamond graders treat inclusions as marks against clarity. In coloured stones they are evidence before they are flaws. They separate natural from synthetic, they carry the traces of heating and filling, and they anchor a laboratory's origin opinion, since a three-phase inclusion in an emerald or a particular silk pattern in a sapphire points to one deposit rather than another. A dealer who says eye-clean is describing what you see at arm's length. A gemmologist with a microscope is reading a biography.

On a lab report

Reports rarely list inclusions in the plain-language section, yet the inclusions drive most of what is printed there. Intact silk supports "no indications of heating"; dissolved or partly resorbed silk supports "indications of heating". Fissures holding oil or resin produce the "minor", "moderate" or "significant" line on an emerald report. Origin is called on the inclusion suite together with trace-element chemistry. GIA, Gübelin, SSEF and AIGS photograph the key inclusions and file the images against the report number, which is one reason a swapped stone gets caught.

Judge inclusions by visibility, position and structural risk, not by count. A crystal buried under the crown facets is invisible face-up; a fissure reaching the girdle can chip in the setting. A truly clean coloured stone is the exception, and in some varieties, ruby above all, a reason for more testing rather than less, because flawless is what a synthetic looks like.

Ask where the inclusions sit and whether any reach the surface. Then look for yourself with a 10x lens, tilting the stone, and expect to find something. If you find nothing, ask why.