How can I make this pattern? (swirl with black lines in it)

[Rebekah]

A mommy wants me to tie-dye a diaper to match this shirt.  I'm fairly new to the game!  So, how might I get this pattern?  Also, I've never used black before, so how do I make sure it comes out BLACK and not gray?

[mustdye]

Here's a nice bit on the wiki...
http://tie-dyewiki.com/wikinew/index.php?title=Spiral

Another effect is to apply a series of colors on the top side of the spiral, and a single color such as black or dark blue to the entire other side. It creates a contrasting backdrop to the spiral. This effect has been termed contrast, stained glass, or cathedral.

[ktaltre]

Tie and dye the swirl and then brush thickened black dye just on the outside of the fabric, then batch.
Also, tie and dye the swirl and then dip it in a black dyebath very briefly, then batch.
I think I've also seen dripping black dye over the dyed swirl.
Also just dye one side of the swirl in the rainbow colors and dye the other side in black.
When mixing black dye, it's suggested to use twice or more the amount of dye powder than usual.
k. taltre

[Rebekah]

Here's a nice bit on the wiki...
http://tie-dyewiki.com/wikinew/index.php?title=Spiral

Another effect is to apply a series of colors on the top side of the spiral, and a single color such as black or dark blue to the entire other side. It creates a contrasting backdrop to the spiral. This effect has been termed contrast, stained glass, or cathedral.

Thank you so much!!!