A leftover transparency made my black lines. Take an ordinary transparency. Notice this is a dirty, junky one. Use an Exacto knife to slice lines in it. 
Take paint and rub it around on top of the lines. 
Your paint will seep and be wonderfully splotchy in a random way.
Here are 3 that I did with just one application of paint. 
I then turned the stencil and did 3 more to create grids.
Great tip! I want to try this.
Great idea and looks good on your pages too!
what a cool technique! I came over here because of your link to the GPP crusade #55 and couldn’t find a way to comment on that particular post, but then started looking around at all your posts. I’m knocked out. Love your work. Can’t seem to find a way to subscribe to your feed, but I’ve bookmarked you and will be back for more! (jealous that you went Valley Ridge and took Michelle’s class! love the things you created there) -Karen