सुवर्णं पूर्वं निकष्य पश्चाद्वर्णिकां निकषयेत् ॥ कZ_०२.१३.१७ ॥
suvarṇaṃ pūrvaṃ nikaṣya paścād varṇikāṃ nikaṣayet
First rub the gold on the touchstone; afterwards rub the reference colour-standard (varṇikā) on it (for comparison).
It fixes the unknown sample’s streak first, then immediately compares it to a known standard under the same surface conditions—reducing dispute and manipulation.