Astanga Hrudaya
धीरः स्वरोऽनुनादी च, वर्णः स्निग्धः स्थिरप्रभः। स्वभाजं स्थिरं सत्त्वमविकारि विपत्स्वपि॥११४॥
the voice should be courageous (loud, commanding attention) and vibrating. The colour (of the skin) should be unctuous / greasy and with good lustre the mind (mental activities) should be natural, firm and not undergoing change even at times of danger (remaining steadfast even in trying situations)
english translation
dhIraH svaro'nunAdI ca, varNaH snigdhaH sthiraprabhaH। svabhAjaM sthiraM sattvamavikAri vipatsvapi॥114॥
hk transliteration by Sanscript