A thick and thin techmique

Hi!
Another of my hobbies is wood carving and I like to do incised carving on signs Recently I came across a horse pattern that was drawn with thick and thin lines showing just the suggestion of the horse which is perfect for my style of incised carving. I don't know what this technique is called but I want to learn it. I will try and post an image of this horse which I bought off the internet so you can see what I mean. In any case I want to learn how to do it and any suggestions on where I can find tutorials, both video and text would be greatly appreciated!



Thanks,
Paul