By just using black and white with some subtle shading  you can make cards out of doodles.  I have been flicking through a great little book that I bought for my dad a short while while ago and got some pattern ideas for doodling and with a little practice I am starting to get the hang of it now.  My hands can be a bit shaky at times so some lines get a bit of a wobble in them but it is great fun to do.  I will get your book back to you soon dad!

Pens:   Black Pitt pen, pencil, paper stub
Card:  Black and white card
Book: Yoga for the brain  A zentangle workout by Sandy Steen Bartholemew