What's the best ink/needle combo for solid black fill?

I'm working on a pattern design on an arm. I got the outlines down pat but I'm having trouble with the fill.
I was using a 7 weaved mag with Kokkai Sumi tribal ink. I could only get a small section to be fully black, the rest
was more shading/washed looking. I tried tight circular movements, slow brush-like strokes and still was "shading".
Any words of wisdom?

[canvasyou]

If you are just starting out -
14round is best for small solid black pieces.
Work small area - then move up to 7mags for similar jobs.
Also check out Zuper Black