Pressing

There are different ways to press your seam allowance. Following is a list of them, and the reasons why you might choose one over others at any given moment.

 Pressing toward the darker fabric

In as much as possible, this is the best choice when sewing your pieces. If you press the seam toward the darker fabric, it is less likely that the seam allowance will show through on the other side. There are occasions, however, when pressing toward the darker fabric doesn't seem practical. In that case, use your best judgement.

 
Pressing seam allowances open

This is a better choice when there are several seams (more than 4) that come together at one point. For example, in a Windmill block there are 8 seams that meet in the center of the block. If you iron the seams open this will reduce the bulk in the center. There will still be a small "bump," but it will be easier to control if the seam allowances are open.

 
Pressing to ease construction

Occasionally neither of the previous two rules apply. When matching up seams, it is sometimes preferable to follow the way in which the seams seem to want to fold naturally. This often occurs when the thread of the fabrics in both pieces are following different directions. On other occasions the construction of the block itself will seem to point the way in which the seams should be pressed. For example, when sewing curves, you will notice immediately that the seam allowances will automatically tend to fold in the direction that will allow the block to lie flat.