Interpreting a design and making patterns for that design is not always a straightforward process. Many people assume that to make 18th century style breeches we would just try to reproduce an historical garment by looking at the few pattern references available such as this one from The Cut of Men's Clothes by Norah Waugh.
The reality is in fact quite different. In the case of our design requirements, we didn't want that kind of period look. We wanted a more modern take on them-a bit more of the seducer rather than the equestrian. That requires a differently shaped pattern. In addition, while looking at the diagram gives you an idea of the period pattern shapes, a cutter needs to have a drafting system or formula to make a pattern.
So what is that period look? What would the breeches in the book look like on the body? If you wanted to make a scaled up pattern directly from it and make a toile you could, but if you look closely at the pattern shapes in the book and look at someone or a photo of someone you can begin to imagine what it will look like on the body.
A little visualization technique.......
First, the side seam is quite straight, and hollowed out. The legs are narrow and you can see that the inseam is quite long - look at the CF line and the front fork. Think about how that will sit on a body. In your mind's eye anchor the pattern at the outseam at the hip, down to the knee. Above that line the fabric will follow the body which has a convex curve not a concave one. Align the front waist line of the pattern along the body's waist and get that CF line sitting vertically in your mind. Remember you would join the two fronts together so that may help your thinking. Look at the leg below the hip and imagine the outseam following the outer leg of the body. Remember, these breeches fit the leg closely. What happens along the inseam at the fork? Align the back waist line on the body- look at the shape of the CB seam. What look will result over the seat of the person now?
I was looking for a good photo to illustrate this but if you've seen some of the BBC's historical movies or TV series, or the truer to period Jane Austen movies you'll see what I mean.
In a nutshell, the excess length in the inseam is great for riding horses, the length and breadth provided by the shape of the back and the CB seam allow for the expansion of the buttocks and thighs while on horseback. When standing though, that excess length sits in the front fork and the excess breadth in back drapes over the seat area.
That is what we wanted to avoid but still have a "period" interpretation. Fall fronts, buttoned leg closures, narrow fitting legs, clean fitting fork and some - but not a lot of - extra fabric over the seat. Tight, but with enough ease that the actor could sit, kneel, lunge, squat, and fence in without problems.
Back to the drafting board!