#rectangular construction

I highly suggest to do the collar work by hand. I have not tested this method by machine, and therefore do not know how this will behave under the static arm of a sewing machine. If someone is interested in trying this by machine, let me know how it pans out.

Start with your body fabric and lining lined up but flat. The collar work will be extremely hard to do once you add the sleeves/gores. The lining method I used is not historical, and I believe it falls under bag lining. Both the lining and the 'shell' were constructed separately, creating two whole garments, then the lining was slid in to the shell. The unfinished seams facing each other. I chose this, as it will also hide all the stitching from creating this neckline, but also was more convenient for a commissioning process as I struggle to finish gore/gusset seams on my sewing machine.

With your body and lining fabric pieces lined up, snip in the neck hole at centre of the body and the shoulder line/seam. The neck hole should be set 1/3rd above the shoulder line as the body fabric with 1/3rd of the neck hole overhanging will be the 'back' of this garment, and the part with the other 2/3rds will be the 'front'.

On the front side, from the centre of the neck hole circle (not the shoulder line), mark a line 30+ cm down. 30cm is the minimum. But whatever this measurement is for you, be sure to maintain this number through the project. Cut along the marked line to create the keyhole/ 'P' shaped slit.

Next, remove the lining fabric from the body entirely. The majority of this collar application will be done on the shell/fashion fabric.

Starting with the 'under' lapel first, this specific set of instructions is only relevant if you plan on having both lapels be silk and want to reduce the bulk from the layers contrasting fabric, outer fabric, and lining fabric. If you would like an easier version of this step, or if you do not care about having bulk, you can applique the contrasting fabric over the top of the body fabric with similar dimensions to the layover flap.

The dimension calculation for the body fabric to be cut away is: [Neck slit length] - seam allowance = length [Neck diameter] - seam allowance = width

For example, the neck diameter I used is 13cm, and the neck slit is 30cm. I use 1cm seam allowances when hand sewing. So the rectangle I cut out is 12cm by 29cm.

Cut out your rectangle under the neck hole but from the side with the most fabric opposite from the neck slit. Next, you will do the opposite calculation to create the replacement part of the fabric.

[Neck slit length] + seam allowance = length [Neck diameter] + seam allowance = width

With the same information from above, the insert rectangle I made is 14cm by 31cm.

Press in 1cm, 'wrong side to wrong side', on the base of the narrow edge of your rectangle. Then line your contrasting fabric rectangle 'right side to right' side along the long edge of the body fabric that isn't the main keyhole slit. Stitch the inserted rectangle down. Fold the rectangle over to fill the space you just removed. Press the seam.

Next, where the narrow width lines up on the base of the rectangle and the body of the fabric, stitch into place, but do not stitch the whole way. Leave a 0.5cm gap on the side next to the neckline slit. This will help when you attach the contrasting fabric to the lining. (Depending on your choice of lining method, sewing this rectangle panel to the lining can happen at this stage (historical flat lining), or after you attach the separate sets of sleeves to their respective shell and lining bodies (bag lining)). The insert should look like this before you trim away to re-shape the neck hole:

Next, cut a rectangle using the following equation, from both the contrasting fabric, and the lining fabric.

[Neck diameter] + (Seam allowance x 2) = width [Neck keyhole slit] + (Seam allowance x 2) = length

The specific calculations I used were: 13cm + 2cm = 15cm, 30cm + 2cm = 32cm. The two rectangles should be width of 15cm and a length of 32cm.

Sew these two rectangles together, 'right side to right side', around 2 out of the 4 edges in a backwards 'L' shape, and leave the other 2 sides un-sewn. Leave these 2 edges un-sewn because the narrow top edge is going to be trimmed down anyway, and the long side edge will be sewn to the body. Trim the seam allowance in the backwards 'L' shape, and turn the panel inside out and press the edges.

Align this new lined rectangular panel up, 'right side to right side', with the long raw edge to the side of the neck slit on the opposite side to the replaced panel. While on the photo it directs to line this panel up [1cm] past where the neck slit line ends, do not do this. Instead, it should be about 0.25cm-0.5cm. Stitch this panel down entirely, ignore the instruction to leave a gap.

Once again, the panel gets turned over, the seam pressed flat, and the panel gets stitched down on the front in an 'L' shape to secure it down.

You should end up with something that looks like this before trimming to bring back the circular neck hole:

Once you're ready to add the lining to the shell permanently, make sure you flip the entire garment inside out and finish any raw seams.

This step is when I was also able to sew the lower lapel to the body lining in my project, with how I was doing the lining. But again, if you're flat lining, you do this step much earlier.

One of the final steps to create this collar, is binding it using 3-5cm width strips of the contrasting fabric. Bind in a similar technique to bias binding.

Using a straight stitch, sew the binding strip, 'right side to right side', on the front side of the body, starting on one side of a lapel panel, leaving ~1cm fabric over hanging the edge, and following the neck hole all the way around to the other lapel panel in a sort of loop-de-loop, again leaving ~1cm fabric hanging over the edge. Trim seam allowance if you please, but you must snip notches into the curved parts of the seam. Then turn the garment inside out, adjust the contrasting fabric so it is pulled out of the neck hole and accessible to you. Wrap the over hang from one lapel inwards, making sure the narrow edge is sitting above the attaching stitch line. Next fold the top unattached side of the strip down to meet the base fabric, then bring the fold that was created down to touch the stitching line. Stitch the fold of the binding down using a whip stitch. Before you reach the end on the other lapel, tuck it's overhang back in, similar to how you started the first lapel. Once everything is whipped down, you may knot off and bury the thread.

And the final finishing touch would be to add a button and loop* closure for at least the top lapel. This button can be a bead/other period appropriate button material, or a button made from matching fabric.