The boundaries of inhomogenities which result from changing conditions during the crystallization process of the diamond are called growth lines or grain lines. Typical manifestations are very fine jagged lines which may be short or may extend over several facets. They only affect the cut grading if they reduce the brilliance (Fig 329-331). Occasionally they are perceptible as planes within the stone's interior; they are then included in the clarity grading (Fig 332).
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| Fig 329 A fine tagged growth line on pavilion facets | Fig 330 A distinct growth line on pavilion facets |
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| Fig 331 Distinct growth marks on pavilion facets | Fig 332 Distinct growth marks in the stone interior diminishing brilliance |
| Twinning lines | Damage |