This technique involves sewing pieces of fabric to a paper foundation following a numerical sequence. Seam lines are traced on the foundation. The pieces of fabric are sewn onto the back side of this foundation (unmarked side - actually the right side of the block). This sewing technique on a foundation allows one to work with very small and uneven pieces with great accuracy, as all sewing takes place along straight lines.
Choose thin, lightweight paper. This is a temporary foundation that will be removed after sewing. You will be setting your machine to very small stitches to make it easier to tear away the paper when you're finished -- using the thinnest paper possible will help avoid tearing stitches out when removing the paper. In addition to paper, you will need a pencil/pen and a ruler.
Preparing the Foundation
To reproduce a design on paper, you can use a lightbox or simply adhere the design you've selected to a window, with the paper on top. Trace the block design carefully onto your paper. Use a ruler and fine-point pencil or permanent ink pen. Trace 1/4" seam allowances around all edges. Cut your foundation just outside these lines.
Many of the designs used with this technique are not always symmetrical. Since you will be sewing on the back side of the design, this means that it will face the opposite direction when finished. This is something you should take into account - if the direction of the block is important, you will have to reverse your design before tracing it onto your foundation.
Cutting the Fabrics
In as much as possible, use 100% cotton fabrics. What's great about this technique in comparison to traditional piecing where templates are used, in this case you don't need to work with precise measurements. Just make sure the piece you are going to sew is at least 1/4" larger around all sides than the space you are going to cover. Triangular shapes are sometimes difficult to gauge, so make sure to cut bigger to begin to make sure you cover the whole area.
Something else I love about this technique is that I can use all those little pieces left over from other projects, that otherwise would be thrown out. You will find you will rarely need to purchase new fabrics for your paper-pieced projects, unless you are considering doing a large project where you want to follow a given color combination. Otherwise, just use whatever fabric scraps you have on hand.