Seams
Senior 2 · Home Science
Seams
Lesson 3 of 5
20 min
Hold a fine cotton voile curtain or a chiffon scarf up to the light and you can see straight through it. Any raw, frayed edge inside a seam would show as an ugly shadow. The French seam solves this: it is sewn twice so that the raw edges end up shut inside a narrow tube of fabric, invisible and unable to fray.
In this lesson you will learn when to use a French seam and how to make one with a standard 1.5 cm seam allowance.
A French seam is a seam in which the raw edges are fully enclosed. It is made in two rows: the first with the wrong sides together, the second with the right sides together. The finished seam is a narrow ridge on the wrong side, and from the right side it looks like a plain seam.
Use it for: fine, light and see-through fabrics (voile, chiffon, silk, fine cotton), fabrics that fray badly, unlined garments, baby clothes (no scratchy edges against the skin) and pillowcases.
Avoid it on: thick fabrics such as denim or wool, where the four layers of the seam are too bulky, and on tight curves, which are hard to turn.
With a seam allowance of 1.5 cm = 15 mm, the two rows must add up to 15 mm. A convenient split is 6 mm for the first row and 9 mm for the second.
A pattern for a blouse in fine cotton has a seam allowance of 1.5 cm. Umutoni sews her first row 5 mm from the edge. How far from the fold must the second row be, and how much should she trim?
Step 1: the total must be the allowance. 15 mm − 5 mm = 10 mm from the fold for the second row.
Step 2: the trimmed edge must fit inside the second row. The trimmed allowance must be clearly narrower than 10 mm, so that the raw edges and whiskers lie well inside the tube. Trimming to about 3 mm leaves a safe margin.
Step 3: check. If she trimmed only to 8 mm, the frayed edge would lie against the second row of stitching and whiskers could poke through to the right side.
Tip
Memory hook: French starts Wrong. Wrong sides first, then Right sides: W before R. If you start right sides together, the finished ridge ends up on the outside of the garment, and the seam must be unpicked.
Why is a French seam a good choice for a voile curtain?
Solution. Voile is see-through and frays. A French seam encloses the raw edges completely, so they cannot be seen through the fabric and cannot fray in the wash.
Give one reason why a French seam is not used on denim.
Solution. The seam has four layers of fabric, which on thick denim would be very bulky, stiff and hard to press. A flat-fell seam is used instead.
The seam allowance is 1.5 cm and the second row is sewn 1 cm from the fold. Where was the first row sewn?
Solution. 15 mm − 10 mm = 5 mm from the raw edge.
Ishimwe finishes a French seam and finds little threads sticking out on the right side. What went wrong, and how can it be prevented?
Solution. The first allowance was not trimmed narrow enough, or the whiskers were not cut away before the second row. Trim to about 3 mm, remove loose threads, and press the fold sharply before sewing the second row.
Remember
Sources and credits
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
