TUTORIAL: Ravel Grading...A Master Tailor's Technique
There are many ways to grade seams. Among them are trimming one seam allowance narrower than the other, turning the scissors on edge to "bevel" the allowances, and using Pinking Shears. But the hands-down most elegant and effective way I was ever shown, is to "Ravel Grade". This was the favored technique taught to me by my Master Tailor mentors during my apprenticeship. You are unlikely to find this technique in any tailoring books, as it is a very esoteric "old world" technique.
Below you will see a photo of 2 pieces of wool, that have been underlined with Pro-Weft Fusible Interfacing to within 3/16-inch of the seam edges. The 2 pieces of wool have been placed right sides together, and you can see (very faintly in blue), that a 5/8" seam has been sewn down the length of the two pieces, on the right.
The first and only step in the "Ravel Grading" process is very easy. Merely ravel off a few threads from the edge of both seam allowances, leaving soft fringed edges. So what does that accomplish? In this example, by completely removing the warp (lengthwise) thread from the seam allowance edges...the fabric there is now half as thick as before!
NOTE--Both seam allowances will be trimmed to 3/8" in some areas like lapel edges and jacket fronts before being Ravel Graded, and will remain "married" (not pressed open). But instead of being the thickness of 2 layers of fabric, one layer has been raveled away resulting in the edge-bulk being totally eliminated...the finished lapel and jacket front edges (collar edges, etc) will be sharp and completely flat after pressing.
In the photo below, you will see the seam allowance pressed open. Notice how elegantly the bulk from the allowance edge has disappeared, because the fabric there is now half of it's original thickness! And to think that all that needed to be done was ravel away a few threads :)
So I ask you...which seam allowance shown below will be far less likely to leave a "pressing ridge" on the right side of a finished garment? The "pinked" side...or the side that was Ravel Graded ? Especially if your fashion fabric is very thick, highly slubbed, or other wise textured? Why the "Ravel Graded" side, of course :)
SEWING NOTES: Medium weight wool flannel fabric is underlined with Pro-Weft Fusible Interfacing, a very lightweight highly flexible interfacing available exclusively at Fashion Sewing Supply.
In case you are wondering...about half the beautifully tailored, very expensive garments that were created in the shop during my apprenticeship were made with fusible interfacings that my mentors imported from Italy. When I created my own line of custom-milled fusible interfacings, I managed to reproduce the same uncompromising "premium" professional quality. If they were still on this earth, I dearly hope that my mentors would be proud of my efforts :)