From the Original Text
“Flat seam—Lay your two edges, whether straight or slanting, exactly even, tack them together with stitches 2 c/m. long, distant 1 to 2 c/m. from the edge, and then back-stitch them by machine or by hand, following the tacking-thread. Cut off half the inner edge, turn the outer one in, as for a hem and sew it down with hemming-stitches. Smooth the seam underneath with the forefinger as you go, to make it lie quite flat.”
— Thérèse de Dillmont, Encyclopedia of Needlework, 1886
Modern Step-by-Step Instructions
The flat seam creates a strong, finished seam with no raw edges exposed. This technique produces a professional-looking seam that lies completely flat, making it ideal for fine garments and household linens where both strength and appearance matter.
What You’ll Need
- Fabric pieces — Cut edges that need joining
- Strong thread — For both basting and permanent stitching
- Sharp needles — For precise basting and back-stitching
- Small scissors — For trimming seam allowances
- Ruler — For measuring seam allowances accurately
- Iron — For pressing the finished seam
How to Work the Flat Seam
- Align fabric edges perfectly, whether straight or angled cuts.
- Baste together with stitches about 3/4 inch long, 1/2 to 3/4 inch from edge.
- Back-stitch permanently following your basting line for accuracy.
- Trim inner seam allowance to half its original width.
- Fold outer allowance over like a hem, enclosing the trimmed edge.
- Hem down the fold with small, even stitches.
- Smooth constantly with your forefinger to keep seam flat.
Expert Tips for the Perfect Flat Seam
- Baste carefully—your permanent seam will follow this line exactly
- Press with thimble or scissors handle before hemming to prevent bulging
- Smooth seam constantly while working to maintain flatness
- Trim seam allowances gradually for less bulk
- Use matching thread for nearly invisible hemming stitches
- Keep hemming stitches small and evenly spaced
- Work slowly—rushing will create puckered, uneven seams
Traditional Uses
Flat seams were used where strength and finished appearance were essential:
- Fine garment construction — Blouses, dresses, and formal wear
- Undergarments — Chemises, drawers, and corset covers
- Household linens — Quality bed sheets and pillowcases
- Table linens — Tablecloths and formal napkins
- Baby clothing — Delicate garments requiring soft seams
- Ecclesiastical work — Vestments and altar linens
- Heirloom sewing — Wedding dresses and christening gowns
Historical Note
The flat seam represented the height of hand-sewing craftsmanship in the Victorian era. It required skill, patience, and considerable time—making it expensive and thus a mark of quality. Professional seamstresses charged premium prices for garments with flat seams, and wealthy households expected them on fine linens and clothing. The technique remained standard for high-end dressmaking well into the 20th century, only being displaced by serged seams and modern finishing methods.
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