You said your own hair is black , so that`s what you have to get..... the timing is crucial ...do NOT leave the product on the hair for more than a few minutes.....try 3 minutes, then rinse it out, allow it to dry and see how it looks....you can re-treat it if needs be......leaving it on too long will result in it going far too dark [unnaturally so] and the only thing you could do then is add colour to your own hair to darken that too ! Just keep it off the lace....you can always just do a ` set` length of perimeter/ area first ,so as to avoid feeling ` pressured` for time..... rinse that bit out/off , and move on to do the next bit and so on...just take your time..that way you won`t make a mess of it. You should use rubber gloves to protect your skin. Let us know how you got on.