(n.) Act of darkening or obscuring.

blackening blocking the light burial burying clouding concealedness concealment covering covering up covertness deception denigration dimming eclipsing extinguishment hiddenness hiding interment invisibility masking melanization mystification nigrification obfuscation obnubilation obscuration obscurement obumbration occultation occulting overcast overclouding overshading overshadowing overshadowment putting away screening secrecy secretion shading shadowing smirch smirching smudge smudging smut smutch smutching subterfuge uncommunicativeness