I’m sorry for the late reply but I’ve been extremely busy all day :(
Answering to your question: I used a black fineliner pen like this one http://www.finelinerpens.co.uk/images/stabilo_black_small.jpg
Ahah tudo bem :)
Actually, I’m currently and totally in love. It’s the first time I feel this way and it feels gooooooooooood.