Slip basting is a hand applied temporary stitch that connect a folded edge to another folded edge or a fabric surface from the fabric's face side (or garment's right side). Slip basting is almost invisible from the right side of the application, cleverly hidden by fabric fold. It provides a convenient way to align a seam form the garment's right side during fitings or when matching intentional prints.
Slip basting is one of those hand stitches you'll need to use in dressmaking when you least expect it. For example, when aligning striped fabric seams where the strips need to match, slip basting will provide a way to keep the stripes perfectly aligned during the machine stitching process - much better then using pins alone.
Slip basting is also used to keep slash pocket openings closed until ready for use. Ot is likely that you have come across pocket openings that are slip basted closed- doing this maintains the pockets stricture, preventing it from stretching out of place until it arrives at the end user.
Another instance you may find yourself using slip basting is when sewing a closed-end exposed zipper into a fabric "slot". Slipstitching provides a way to keep the zipper teeth aligned evenly in the middle of the slot with the same amount of zipper tape showing on both sides of the zipper chain.
To apply a slip basting stitch (fabric fold to fabric surface):
1. Fold and iron one of the seam edges and align the fold to the corresponding seamline on the other seam edge,
2. Insert pins perpendicularly to keep the fold aligned to the fabric surface underneath.
3. Keeping the fabric layers aligned, insert alternating stitches from the fold to the fabric surface underneath. Insert the stitches such that they are sandwiched in between the fold, catching the same-length stitch from the fabric surface as shown.
When unfolded, the seam should look like a regular hand basted seam.
4. At this point the seam can be machine stitched next to the hand basting, following the designated seam allowance,
Using slip basting to sew a striped fabric seam will result in perfectly transitioning stripes across the finished seamline. You can use slip basting any time to need to sew a seam intentionally positioned/intersecting prints.