Originally Posted by MsEithne

I forgot to add how I use the scalpel to rip.

I hold the seam closed and only cut the thread on one side. I slide the tip of the scalpel under every third or fourth stitch and then just turn the scalpel upwards slightly. The edge is so sharp, that's all the effort it takes to slice through the stitch.

Then I turn the seam over, take hold of the uncut thread and pull gently. If I've done it right, the uncut thread just slides right out without pulling or wrinkling the fabric. I use masking tape sticky side out over my finger to grab the cut threads on the other side. If it doesn't slide out with a gentle pull, then I go back to the original side and cut a lot more stitches.

This causes the least amount of fabric damage possible. Even fine silks can be ripped this way leaving only the needle holes (which can often be steamed out). On cotton, once what used to be the seam allowance has been pressed flat again, there's usually no sign at all that it had ever been stitched.