The best is when you can design an image that results in both a stencil and mask. For instance, see HERE.
Often, you actually have to alter an image, and cut it twice to yield both a stencil and a mask. Like the text above....it needed small portions to be removed in order to be a stencil. The black parts get cut out. If the are any "islands", portions that aren't connected to the main background, they will fall out with the cuts. In order to preserve the image, in this case the letter forms, you will need to alter the image. I've indicated in red where the cutting should stop to preserve the "islands". Imagine those red markings as white and you can see how the stencil is formed. For a mask you need to reverse your thinking. This time the black is going to be the end product. All parts need to connect so you will have to modify the original text by extending connectors. Imagine the green markings as black and you can see the mask.
Here is the completed stencil and mask. I cut them from acetate with an exacto blade. The image was printed directly onto acetate. (I also like to use a heated tip stencil burner.)
Kari has initiated an online blog party. It's a great idea as I believe networking and building communities is one of the perks of blogging. If you are new here and just hopped over from Kari's party then I welcome you. You'll find my current obsession is utilizing stencils and masks with spray paint in my art, and you will find many blog posts here about that subject. I recently compiled most of the images into my "Sprayed!" album in the left sidebar. I run another blog called the GPP Street Team which was featured in Artful Blogging. You are invited to come over and see the fun we are having there. It is an example of an online community that is building itself. This months crusade is about adding music to your blog, and last month we were all about Mail Art. Thanks for coming by! (Oh, and if you haven't been to Kari's site yet - she has been adding dozens of links to artful bloggers who have joined in the party!)
P.S. DUH! Since this is a party i should be giving something away, right? I have extra copies of Artful Blogging...so leave a comment if you want to be in the drawing for a copy of the magazine and some other goodies from my studio. (Collecting names through Thursday @ midnight EST)