The Hong Kong finish is a classic seam allowance finish used on garments which have underlining instead of lining. The seam allowance edges are encased in bias tape strips made from the underlining or any lining fabric. You could add a designer touch by using strips in a contrasting color to the garment or using your favorite color for a little surprise and a moment of joy when you see it.
Recently I made a dress out of a beautiful cotton jacquard which needed underlining for stability and modesty. I choose to underline the dress in black cotton lawn and made my bias strips for the Hong Kong finish out of the same cotton lawn. I did make a change to the pattern in leaving the sleeves unlined. So the sleeve ruffle you see in this photographic explanation is not underlined. I added the Hong Kong finish to the ruffle anyway to encase the unraveling seam allowance.
The finish is easy enough to do. Match the edges of your 1″ bias strip to the raw seam allowance edge and sew together using small stitches and 1/4″ seam allowance.
Because my ruffle is already hemmed I folded up the bias strip onto itself. Better yet, next time I folded the bottom edge of the strip around the bottom edge of the seam allowance. (You learn by doing, right?)
Press the bias strip away from the seam allowance. (I put in the white paper so you can see the edge of the strip)
Turn the bias strip to the inside over the raw fabric edge and press. The bias strip now encases the raw edge of the fabric.
Stitch in the ditch or close to where the bias strip and the garment meet on the right side of the seam allowance, again using small stitches (not tiny, just small) and catch the bottom edge of the bias strip binding (the edge laying under the seam allowance). The bias strip edge behind the seam allowance will be raw but should not unravel since it is cut on the bias. Press.
Remember, You are just sewing the seam allowance of the garment; not the garment and not sewing the seam allowance to the garment.
Repeat on the other side.
The Hong Kong finish takes a little more time to apply than zig zagging your seam allowance edges or not finishing them at all but you will be pleased with the couture touch your garment now has.
Next time I think I will use a fun color to finish my seam allowances or maybe I will just zig zag them.