I had a ton of trouble with this "easy" background. I didn't copy the materials like I should have, so this was a real trial and error process. As always, click on the photos for a larger view.
Substrate (copier paper, paper bags, card stock, etc)
Brush (foam or bristle, not shown)
Plastic bag or something to protect your work surface
*I show bottled acrylics in the photos, but I ended up using some cheap craft paint in a jar to get the results I wanted. I'm not sure what kind of acrylic paint Claudine used, but I'm sure it was PROBABLY Golden tube acrylic, something I don't have.
1. Place a large amount of acrylic paint on your substrate.
2. Spread the paint using a brush. Cover your paper completely.
3. Immediately sprinkle baking soda into the WET paint. As you can see from the photo below, I accidently dumped the baking soda when I was taking the photo. After I put the camera down, I placed the baking soda in my hand and sprinkled it evenly all over the page.
Sprinkle baking soda over entire surface. Allow to dry flat.
4. When completely dry, brush baking soda from the page using a dry towel or cloth. A brush will not remove the baking soda, so you'll need something more substantial.
Here's how I used this particular piece:
I really didn't like how the background turned out, so I got some cheap craft paint and slathered it on a sheet of copier paper. I put a LOT of paint on the page, then added the baking soda. I used red paint, but the baking soda changed the color dramatically. I made two sheets, one with brush strokes and one that I pounced the brush strokes out. I really like it the best.
Top image: with brush strokes showing. Bottom image: with brush strokes pounced out.