Mini Tutorial: ​How To Finish An Armhole Edge With Decorative Trim

A decorative trim finish works best of used with low fraying or no-fray fabrics that maintain enough strength and stability along their cut edges. Given that the trim hides the armhole's raw edge as opposed to enclose it, the fabric itself has to maintain enough structure and durability on its own.

1. Once the garment's shoulder and side seams have been stitched and clean finished, apply a straight stitch along the armhole edge at about 1/4" away form the fabric's raw edge. Apply the stitch form the garment's wrong side as this will provide more comfort. during the application process. This is stabilizing stitch is called staystitching and will play an important functional role in preventing the armhole edge from loosing its durability and stretching out of shape during the construction process and garment's life cycle. 

2. Fold one of the trim ends inward at about 1/2" or 1/4" and align the fold edge with the garment's underarm seam, form the garment's right side as shown above. The body of the trim should fully cover the armhole's raw edge. Insert a pin perpendicularly to secure all layers together.

3. Continue aligning and pining the trim to the armhole's raw edge, ensuring that the trim fully covers the edge throughout. 

4. When arriving at the underarm seam, leave some trim excess taht is about 1/2" past the seam and fold this excess inward aligning the resulting fold with the garment's seam, abutting the other folded end of the trim. Insert a pin perpendicularly to secure the layers. 
It is highly recommended that you hand baste the decorative trim accurately in this position, to prevent it form shifting out alignment during the stitching process. 

5. If your trim can be machine stitched, topstitch the trim form the a garment's right side following one of the trim's edges or linear structures as a guide. 

6. Once fully stitched, remove the hand basting using a seam ripper. To seal the trim's folded ends at the underarm, slipstitch them together by hand using a matching color thread for an invisible application, 

If the trim cannot be machine stitched, attach it by hand using either a prick stitch on a blind stitch (slipstitching or hemming stitch). Your technique should be chosen based on your trim and what will provide the strongest leasts visible connection. In the example pictured above, a prick stitch is used to attach the decorative trim form its face side.