Typically, black and gray tattoo work consist in using different shades of black. By diluting the black ink with distilled water in various proportions, creating a "wash", lighter shades can be produced. Although this is the popular method, some artists mix white ink with black, but it is not the traditional method.
Other things that need to be kept in mind are needle depth and speed. For a lighter shade, hand speed can be increased. After a tattoo has been completed with varying degrees of black, highlights are often added using white. White ink can also be used to smooth out sharp transitions between the different shades.