Probably be a good idea to see if you can wash off the BJ you already have on the surface with turps, then add some lamp black universal tint to the BJ and re apply to the whole thing again. You can seal the BJ with shellac then apply polyurethane or seal it with our U-Beaut
Hard Shellac and if the colour still isn't what you want add a little of the lamp black to the shellac for a second and third coat, sand lightly with 600-800 grit wet n dry then apply a final coat of clear
Hard Shellac and finish off with
EEE-Ultra ShineHope this helps.
Cheers - Neil :)