I drew this long time ago and I don't remember the details. I used mechanical pencil HB, probably 0,7mm, with a stylus of a cheap firm and kneadable eraser. Technique? I don't know, I can't descibe, how I do this. My eyes looks and my hand drawing. Sometimes my second hand have to touch and fell (for example on my own dog ). Look at my scrapbook - maybe it will help you somehow.