It depends on what paints you tend to use as the mix will vary with different paint brands. Here is a picture of the Tamiya 1/16th machine gunner beautifully painted by Modelsinfinescale (Patrick) some time back and should be a good guide. The face is done with artist oils and the overcoat if I remember correctly maybe either oils or acrylics. Most likely oils. Its been a while. The overcoat is not pure black but rather a mix of grey and black to allow for the painting of highlights and shadows. You can either mix brown or buff to black to make it slightly grey so your shadows can be pure black.
1/16th MG