I don’t remember what or when I was sewing. All I remember was staring at the unfinished garment on the form and seeing that something looked funky and not right.
“What’s wrong… what’s wrong?” I thought, stepping back to get a “monet” of the garment (monet is Cher Horowitz’s word for glancing at something from afar).
The garment was pulling in all sorts of directions at the seam and the seam allowance was not lying flat.
“You dweeb! It’s a concave curve!” I said to myself.
Defined in non sewing terms, a concave curve is a curve that is hollowed or rounded inward like the inside of a bowl and a convex curve is a curve that is rounded like the exterior of a sphere or a circle. An easier way to think of a concave and a convex curve is a concave curve is a valley and a convex curve is a mountain. Also, things that “vex” you tend to stick out and caves tend to be things that other things are stuck into (like belly buttons!).
When it comes to sewing, concave and convex curves present the biggest challenge when it comes time to press seam allowances.
Depending on whether the seam is a concave or a convex curve will determine whether to clip or to notch the seam allowance so that it lies flat. For both concave and convex seams, first trim seam allowances to 1/4″ after sewing. After, if the seam is concave, cut v notches at regular intervals so that when the seam allowance is pressed back towards the stitching line, it will lie flat. The reason why the seam allowance doesn’t lie flat if V notches are not made is because the length of the edge of the seam allowance is LONGER/GREATER than the length of the stitching line / when the seam allowance is pressed back towards the stitching line, the edge is too long in comparison to the stitching line.
If the seam is convex, clip into seam allowances notches, being very careful not to cut through seam. The reason why the seam allowance doesn’t lie flat if clips are not made is because the length of the seam allowance is SHORTER/LESS THAN the length of the stitching line / when the seam allowance is pressed back towards the stitching line, the edge is too short in comparison to the stitching line. CUTTING into the seam allowances and allowing it to FAN OUT increases the length.
Does this make sense? Most importantly, do you understand why clipping and v notches are made (because the length of the stitching line and seam allowance edge are different)?