Currently I am drafting a 5-gore underskirt or petticoat, with dust ruffle and flounce, according to instructions in the 1911 textbook, Textbook on Domestic Art. It has been an interesting process. The instructions rely on sizing up or sizing down a draft based on proportions taken from a model skirt. Since my body no longer follows the suggested proportions of a waist 15" smaller than the hips, whoops, well, something interesting happened to the results, and I am still mulling over my solution and whether it was the right one.
Instructions for drafting and then making up the skirt appear on pages 74-85. You can find the orginal source materials, in full, on the Cornell University Home Economics Archive (Hearth), at http://hearth.library.cornell.edu/.
By the way, the text bases a street skirt on the same draft...you learn how to do variations to make a pattern endlessly useful.
Drafting the Petticoat
Here is the skirt draft illustration.
I found the instructions to be clear and simple. First, the textbook discusses the proportions necessary. From these, if you like, you can calculate the waist measure for each gore, the hip measure, and the length to the skirt bottom (minus the dust ruffle). However, you don't have to do this: the step-by-step drafting instructions have you make these measurements as you draft up your pattern on paper. I laid long lengths of freezer paper on my big Hancock's measuring and pinning board and drew the drafting dots and lines with pencil and ruler.
The Proportions Problem Appears
When I finished the back gore, it looked too narrow compared to the model drawing, which had quite a flare on it. What was going on?
Remember that the draft is based on proportions, right? Well, oh dear, I have a thicker waist of 30" compared to the model's 24". So when I drew the oblique line from waist to skirt bottom that forms the back of the gore, I got less of an angle than a woman with a smaller waist would have. What to do?
The text states on p. 76 that "(t)he average width of an underskirt on lower edge, before dust ruffle is attached, is between 2 1/2 and 3 yards, for the average person, unless very wide skirts are in vogue". For the model that's 90" inches of "sweep", as the term has it.
Well, I bet mine wasn't any 90". It didn't have the right flare at all, and I had checked my math, I hoped.
What Textbook on Domestic Arts Suggests Doing
The textbook writer knew that some girls would have thicker or thinner waists. So on pp. 83-84 it says,
"If more fullness is desired at bottom of skirt, increase width of each gore by starting 1/3 of its length below the waist line, on each bias side. [If you read Harriet Pepin's Modern Pattern Design on http://www.VintageSewing.info, you'll see this mode of splitting the angle of the gore into two parts in action.] For less fulness, decrease....(T)he width around bottom should be in good proportion to the height and size of hips of each individual, even when extreme fashions are in vogue."
Aha! So I was supposed to add inches to the sweep by adding width at the bottom of each gore. Okay, how to do it?
Solving the Proportions Problem...With Algebra?
So I rummaged in the brain and remembered the simple algebra formula for coming up with a proportion. The model waist of 24 is to model sweep of 90", as my waist of 30" is to X. I solved for X and it said I needed 112" of sweep, distributed around each side gore and the back gore. By the way, that comes to the 3 yards circumference maximum suggested by the book.
I measured the bottom width of the side gores and the back gores with a ruler...but didn't know how to distribute the inches needed to make up 112". That's when I had a, perhaps, bright idea.
Using the proportion formula again, I calculated the waist/sweep proportion of the model back gore, and compared it to my waist/sweep propertion. Aha: I was 4 inches short on my back sweep measurement.
Surely the side gore would have the same problem, but it didn't. The results were the same, no matter how many times I redid my math.
Further, the four inches I needed in back, when added to the sweep of the other gores, added up to the ideal 90"!
So, suspecting I had drawn my lines wrong on the gores, I redrafted them. (Oh, how boring that was.) But no! I had done it right.
When That Doesn't Work Perfectly, a Middling Solution
Frankly, I don't know what error I made or what principle of geometry is in effect that causes the bottom width of a gore to come out differently when you do it by math versus drawing it out.
But I did decide what to do. I kept that 90" sweep, as being befittingly narrow for 1911. Then I distributed 2 inches of extra to the back gore and 1" each to the side gore. If when I build it in muslin it makes me look dumpy, well then I'll redo it with a 112" sweep, and I will have learned how proportions affect the line of a dress in a visceral way.
A Final Notice to Teachers: Make Algebra Actually Apply to Something and Perhaps We'd Take to It More
I'll see how it turns out! Oh, by the way, had someone back in high school applied algebra and geometry to something interesting like sewing instead of to endless drills, I might actually have liked math class. All you teachers and homeschoolers out there, take note!