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A lot of people struggle with developing patterns for pants. There always seems to be problems: The crotch sags, the butt sags, the waist rides up, the crotch rides up; no matter what they do they just can not get that pattern to fit properly. What is the cause and how can we fix it? This article aims to answer just that by taking a logical and theoretical approach and examining just what those curves do and where to put them.
The Crotch Seam
First of all, I think it is important to establish that the negative space theory concerning the shape of the crotch seam is more myth than truth (for those of you not familiar with the theory, the idea is that a perfectly fitting crotch seam will follow the curves of the body-i.e. negative space of the body). Consider if this idea were applied to a straight princess seam- the two are similar: the crotch seam curves out from under the derriere and curves back over, and a princess seam curves out over the breast and over.
Here is what the negative space of the bust would look like:
And here is the resulting pattern using the negative space theory:
Notice how instead of a dart removing fabric, there is the equivalent of a gusset adding fabric. Experience tells us that a gusset rather than a dart over or under the bust leading to the bust point will not shape the fabric closer to the body, but will flare out. In fact, over the widest point (the bust point for the bodice), the shape must be inverse (inverse considering the three dimensional shape, not simply the side-view- sorry if this is confusing).
If this is true for the bust, it out to also be true for the derriere, and will hold true also for the front crotch seam if the person has a tummy that curves in under the waist seam. Over the widest point of the curve, the seam will inversely follow the curve if under the curve, the seam follows the curve (and vice versa).
Front Crotch
Because the front is generally not affected by the inverse curve rule, it is simpler to understand, so I will begin here.
In understanding how the front crotch seam works, one must start with two concepts. Firstly that extra width in the pattern cannot be added just anywhere- it will add width in that particular area, and in pants, this will drastically effect the fit. Secondly, grain is key for pants.
These two concepts lead to an opposite effect in the front crotch seam. If more fabric is needed to go around the waist in front, extra fabric should not be added in the front. The center front will be pushed out in the tummy and the grainline (and front crease) will swing backwards towards the body which in turn would cause the side seam to be crooked and cause ugly wrinkles in the front along the thighs. The fabric will also curve inwards at the front crotch, causing wrinkles there as well.
Counter-intuitively, if a person wants to adjust for a tummy or wants to correct such wrinkles, she ought to remove fabric from the front crotch so that the pants will hang straight down from the waist (and because this removes from the overall waist measurement, more fabric should be added at the sides).
The reverse is true for the curve that is much more than the curve of the tummy. The seam will be pulled back to lie close to the body. This also pulls on the grain and the creaseline. These as well as the sideseam will be pulled forward, causing wrinkles at the back crotch and thighs, especially just over the back of the knees.
This the shape of the curve is a continuum: one end leads to wrinkles on the front; the other wrinkles in the back. Somewhere in between is the perfect fit.
Back Crotch
Now for the bigger problem- the back curve. This is a bit different because the buttocks will prevent the looseness (extra fabric on the inside of the original curve) from hanging forward as much, although tightness (not enough fabric on the inside) can still pull the grain to the inside thigh and the sideseam to the back. Compared with the front, however, these are not as obvious.
There is another issue at hand-the darts in back which are necessary because the measurement from the waist to the hips over the highest point of the buttocks is longer than the measurement from the waist to the hips along the crotch seam. Thus a dart over this highest point is necessary so that the fabric does not strain around them. To create the darts, one must remove some of the angle (this angle will slant towards the sideseam from the crotch due to the inverse nature of curves) of the upper back crotch curve (which is essentially a dart, cut in half) and add that width to where it is necessary.
However, it is possible to remove too much of the angle. The amount changed should reflect the difference of the aforementioned measurements (plus ease). So if the angle exceeds this difference, there might be fitting issues particularly due to the fact that the back crotch seam runs lower than the darts. This causes bagginess in the back because the darts account for a larger curve of the derriere than it ought to. I also suspect that is in part the cause of “mono-butt” as described by Kathleen Fasanella in her post, Jeans Fit Lousy These Days.
This is because jeans these days do not have darts (only a little shaping in the yoke if there is one), so in order to fit over the curve of the “buns” and not have all the extra ease sucked into the equivalent of a center back dart, this center back angle is straightened (and because the extra fabric is not sewn into sideback darts, the waist ends up loose and may stand away from the body. To counter some of this effect, the waistlines are lower and many jeans are made of a spandex or lycra blend). As a result, the crotch curve is cut too wide, especially at the midpoint of the most curve. Thus, no bifurcation!
Crotch Undercurve
Which brings us to the most important area for fitting pants- the crotch undercurve. This curve is another counter-intuitive area. The other rules from the upper crotch seams still hold true for the lower sides- removing fabric will make the seam looser and adding fabric will make the seam tighter (the sides must be adjusted to maintain the overall balance, however). These pertain to the width. In this area is another factor- depth. More fabric under the curve leads to a shallower crotch seam which is short and tight. Less fabric means a deeper curve which can be much too loose and low. Thus this area of the crotch seam must reflect a person's personal width and depth (plus ease and sitting room).
However, not only must the overall width and depth be correct, but the width and depth for the front and back curves individually. For example, the curve could be too shallow and narrow in front, but too deep and wide in back (or any combination of the aforementioned).
An infamous problem with this front curve is known as camel toe (see Kathleen Fasanella's post on the topic here) It is caused by a too narrow front crotch, the reasons for which Kathleen Fasanella explains in in her second post.
The Inseam
The inseam, particularly in the thigh area, is also tricky. While the outer side seams for the front and back might be similar, the curves of the inseam differ from front to back. This is because the thigh tends to be straight in front (from a side view) or even curving out for those with muscular legs, but in back, the thighs curve inwards from the derriere to the knee, particularly just under the derriere. This is reflect in the pattern pieces.
The front pattern piece will generally have a fairly straight inseam that is a little curved at the crotch (this is because the thighs don't meet together at the crotch, even if it appears so when the person is standing straight with her legs together; once she starts moving, it's obvious that the thighs are not joined together).
The back pattern piece will have much more of an angle, particularly if the pants are fitted in the back (like jeans). However, if this back angle has more of a slope than that of the thighs, “smile” wrinkles will form along the insides of the pant thighs. This angle can also have too small a slope, meaning that there is too much fabric in the inside thighs, and “frown” wrinkles will form in the same area. Between these two is a range of fitting- none is necessarily wrong. Jeans tend to follow the curve of the back thigh closely, slacks follow much more loosely, and trousers generally fall straight from the derriere.
Similar problems also occur for the front inseam, also indicated by “smiles” and “frowns.” For a practical example, look at Kathleen Fasanella's post on a jeans fitting problem. Notice how the wrinkles run across the front in a v-shape towards the knees indicating not enough fabric at the front inseam around the knee around, which is partly due to extra looseness right under the crotch seam. Notice how the pattern resembles a back inseam by how exaggerated the curve is. Such problems are not only indicated by wrinkles, but also by a distorted grainline.
A Practical Example
While theoretically, pants may seem almost straight-forward, in practice getting the perfect fit is not, especially when working from a commercial pants pattern. Wrinkles are a good indicator of problems, yet often it is difficult to tell exactly what is causing the wrinkles- it may be several factors or something so elemental to the pattern that they cannot be pinned out.
Unfortunately, I have not documented my attempts at pants, so here is a post of what fitting problems a seamstress came across with a commercial pattern and how she solved them. I think that in this case, at least three problems are evident, all though it's hard to tell with just one angle- the undercurve is too shallow, the back inseam does not have enough ease or is too sloped, and perhaps even the front crotch seam could be straighter. Notice how some of the wrinkles, particularly the exaggerated ones right under the back crotch, vanish when Sigrid deepened the crotch seam. Notice how when she widens the overall pattern (and thus increasing the fabric width in the inseam), most of the wrinkles vanish. To solve such problems, a good measure of persistence is necessary. Starting out with a good pattern or drafting one's own is certainly helpful as well!
A big thank you to Kathleen Fasanella and Sigrid for allowing me to incorporate their posts in this article!
If you liked this article, you might like these patternmaking books:
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Wednesday, 03 February 2010
A lot of people struggle with developing patterns for pants. There always seems to be problems: The crotch sags, the butt sags, the waist rides up, the crotch rides up; no matter what they do they just can not get that pattern to fit properly. What is the cause and how can we fix it? This article...
© 2010 - Fashion Students Online
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