स्थिरः परुषो विषमवर्णश्चाप्रतिरागी क्रयहितः ॥ कZ_०२.१३.२४ ॥
sthiraḥ paruṣo viṣamavarṇaś cāpratirāgī krayahitaḥ
A streak that is stable, rough, uneven in colour, and lacking counter-tint is suitable for buying (i.e., warrants purchase-side caution/discount).
It legitimizes lower offer prices or stricter acceptance when the state/merchant is the buyer, reducing losses from substandard metal.