So I'm going to henna for color.  I mixed henna w/ lemon juice, coffee, and water.  It's been sitting for about 12 hours now.  My hair is black and I want it blacker if possible w/ the added shine.  I don't have indigo to add at this time.  My question is this: Do you think it will make any difference color wise if I let it sit longer or have I let it sit long enough to get as dark as it can w/o indigo?  Thanks, Ladies!