SID is short for Stitch-in-the-Ditch. The “ditch”, in quilting terminology, is the seam line between two patches on the right side of your quilt top. When quilting the top, stitching in the ditch will make your patches stand out and give crisp and clean lines to the finished quilt.
When SIDing, the object is to have your quilting be as invisible as possible. Since seam allowances are generally pressed to one side, you sew on the ‘low’ side (the one the seam allowance is NOT lying under), as close to the seam line as you can. When the fabric relaxes after the quilting process, those stitches will lie somewhat underneath the ‘high’ fabric and hardly been seen.
The general thinking is to use a thread color that matches that low side fabric. Let’s say my ‘low’ side is black and my ‘high’ side is cream. Most people would use black thread to do the SID.
What I’ve found, however, is if I accidentally stitch up onto the ‘high’ side of the ditch, the contrasting thread is really obvious.
I now prefer using a thread color that matches the ‘high’ side. Since I’m sewing right next to the ‘high’ side, the lighter thread is not obvious on the dark ‘low side’ fabric. And if it does jump up on the ‘high’ side fabric for a few stitches, the mistake can hardly be seen.
Since you often have multiple fabric colors, or the low side of the ditch shifts from dark patches to light patches depending on how the seams were pressed, you won’t always be able to choose the ‘perfect’ thread color. And many people like to use invisible or monofilament thread to SID. But perhaps this will give you something to think about next time you choose thread for SIDing. Let me know if it works for you!