Having successfully finished the fronts of the trousers, it’s time to turn attention to the backs.
Back fitting
First thing I need to do is put some reinforcing interface around the areas that will be sewn. These are around the back pockets and a small fitting dart that goes between the pockets and the waistband.
Looking closely at the GAP trousers I find they did this in one piece, so I copy the shape and cut my interface in a similar way (see right). Because the interface does not cover the entire area of the fabric I am stiffening, the edges are cut with pinking shears to avoid a line being visible from the right-side of the finished trousers.
I then iron the interfacing in place and sew the darts (see above left). I don’t bother to trim the seam allowance of the darts because they are so small and it may only weaken the trousers. I press the darts flat from the right-side (see above right).
Back Pockets
I am now ready to do the back welted pockets. Setting welted pockets like these has become a regular thing for me, but this time I need pay a little more attention to detail; the welts are a little finer; the pinstripes means cutting needs to be more precise; and because the trousers are not fully lined, the pocket bags will be exposed and will need to be much neater and have no exposed raw edges.
The pieces I prepare are two interfaced welts, folded and pressed in half; one interfaced pocket facing; and a button loop made from pinstripe fabric (see left). I have carefully cut and pressed these so pinstripes will be visible on each.
I then mark the position of the pocket (see below left) and sew the welts on the right-side, flipped upside-down (see below right).
I then cut between the two welts (see above left) and snip to the ends of the stitching in a Y shape at each end (see above right).