Why jean legs skew

twill_denim_markerMy friend and esteemed colleague -but not my competitor- Valerie Cooper called me to ask if I knew that Cone Mills and other denim producers deliberately introduced skew into the denim they weave during the finishing process. As many of us know, skew (sometimes called torquing) is something to be avoided. This was news to me! Oh say it isn’t so! Just goes to show how much we knew. They do and it’s a good thing.

Here’s the back story which some of you know already (and more). Denim is a twill weave. The nature of twill weaving shifts grain under required pressure dictated by the weave itself. If you look at vintage denim, the legs skew badly. Today, not so much because -and this is what we didn’t know- Cone Mills and other producers started to introduce skew deliberately in the finishing process to compensate for the shift that is inherent to twill weaves which reduces the overall skew. You know, a course correction (talk about defying the laws of physics and not thinking through things to their logical conclusion). I knew they did something to get it back into shape, but hadn’t really thought about it much.

The other thing I’ve always known but didn’t know why (in order to control it) was how laying out pattern pieces on the goods can introduce skew in twill weaves. That’s useful information with any kind of twill weave (to include gaberdine etc). It turns out that to make the most of the twill engineering, manufacturers need to design markers to place pieces that sew together directionally and in different zones across the width of goods (see sample marker at right). I slapped my forehead because this is but another expression of the same problem I thought Claudine’s blouse had at the center back seam; that it seemed she’d cut it from opposite sides of the goods along the selvedge (I don’t include all of the Refine My Line analysis on the blog but it’s in the forum). Of course, old schoolers who specialize in denim production know how to plan these kinds of markers, yet another reason I suggest using a specialist. Anyway, I thought this all so very fascinating.

In today’s journey across the web doing research, I came across other sites that talk about denim weaving more specifically but designed for laymen so I think you’d find it interesting but not have your eyes glaze over with engineering details. This glossary was interesting and well done. I’d seen all the pages on this site previously but lacked an excuse to link to them. There is also a tour of Cone Mills and an interview with a spokesperson who confirms and denies given rumors. Probably the most popular one being that the Japanese bought all the Cone Mills selvedge denim looms. The source said they didn’t. It is amazing how many sites out there are dedicated to jeans production. Some sites are downright loopy. They find what is rightfully a defect but not knowing such, elevate it into a desirable feature. And I’m not even talking about things like ropey hems. I’ve given up on that one and concede that beauty is in the eye of the beholder.

Related entries:
Pop Quiz: Denim Quality
Trip report: Denim processing contractor pt.1
Denim laundry contractor pt.2
Pop Quiz: Denim Quality pt. 2

OT: Yes I saw the New York Times article on designing your own clothes via the web from Stephanie Rosenbloom who has recently become a veritable expert on all things apparel. First she became a sizing expert (I was not amused) and now she’s become a jeans designer -which hasn’t restored my jovial good humor either. Suffice to say, if you measure as she instructs in the accompanying video, you’re likewise doomed to be less than amused with the results. Now everybody’s unhappy. Except for Stephanie and the NYT who got a story out of it. If you want to know what went awry, I created some screen shots. The post I wrote about garment measuring is probably a better choice for designers.

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  1. Theresa in Tucson says:

    Kathleen, if I’m reading the marker correctly, all the size 36 x 32 are going in one direction and all the 38s are going in the other? Would I be correct in assuming if I had the 36 x 32 right side going in the opposite direction as the left I would be introducing skew? I make my own jeans and like to lay out everything in a with/nap layout but I have worn jeans that were badly skewed. Thanks for an informative post.

  2. Paul says:

    The video from the NYTimes was a hoot. Actually, I am surprised the jeans fit based upon the way the measurements were taken. The video reminded me of the adage; the blind leading the blind.

  3. Anna says:

    I really want to see how the torque into is introduced to the finishing process. I want to see the math. What a good idea.

    The marker strategy is new to me as I rarely pattern for twill, but makes sense. I always enjoy this type of mental floss.

    “First she became a sizing expert (I was not amused) and now she’s become a jeans designer -which hasn’t restored my jovial good humor either. ”

    Soon as I read that I knew it meant endless entertainment for me and I can’t wait to follow the link trail.

  4. Kathleen says:

    Theresa: As I mentioned, I hadn’t put together the advice I’d given Claudine with this one but it’s the same concept (why I slapped my forehead). Going by the documentation in the forum, note page 33 (page 5 of the pdf) which explains quadrants. Cuttable width is divisible by four, left to right quadrants numbered 1-4. Paraphrasing, front and back panels for the same leg should not be cut from the same quadrant.

    What isn’t stated (an experienced marker maker would know), is that twill is a one-way -of a sort. Namely that all pieces from one garment should be cut in the same direction to prevent shading.

    What this means for your purposes in cutting a one-off (to include anyone wanting to make a single sample) is you can’t put all pieces of a single pair running across cuttable width if you reverse direction of any given pattern piece. This is only possible for the tiniest of sizes because the pieces of larger sizes are too wide for the cuttable width (due to crotch fork). Meaning, if you don’t want a lot of waste, you should cut two separate pairs at once. Obviously you would reverse piece direction of each given pair for better yield, carefully sorting them to make sure each are joined to the respective unit.

    …which brings me to a recent dinner convo twixt DH and I about bundle controls, affixing a label to each cut piece to indicate pairing of individual units (pg 117 of the book, also). HTH

  5. sally says:

    I was taught to pivot the grainlines on the jeans patterns depending on whether it was a left hand or right hand twill.

    We would make 4 distinct pattern pcs for the legs: 1 left ft face up, 1 rt ft f.u, 1 left bk f.u, 1 rt bk f.u. and depending on whether it’s a left hand or rt hand twill, you pivot the grain line on the pattern pcs. about 3/4″ at the leg opening so the grain lines “swirl” around the legs similar to how bias dresses are cut.

  6. Theresa in Tucson says:

    Ah, that makes sense, Kathleen. I did find and read the pdf when I was on the forum. Thanks for the explanation. For my purposes, cutting out two pair and marking them would be easy since I prefer to make up multiples when I’m sewing something like jeans. I’m fiddling with a trouser pattern right now and not enough fabric. I’m going to piece the fork to get it all to fit. That appears to be a common fabric conservation method in my tailoring books. Since the pants are for me, I figure, why not, although I doubt if anyone would do that in RTW.

  7. Kathleen says:

    Alison: I wrote a comment earlier but the system ate it -disappeared who knows where.
    Fit is subjective, these pants are probably mono-butt jeans, that being the paradigm these days so even if Sally measured me, I wouldn’t think the jeans fit well. Fwiw, I don’t think Stephanie’s jeans came out badly at all considering. I might try it just for the heck of it. I think $77 for a custom made jean is a bargain.

    Theresa: In the olden days, piecing a fork was something to be ashamed of. Iow, in the era of there being less differentiation between budget, moderate categories etc. Piecing a fork was considered “cheap”; that if you were going to do that you should use a gusset. I don’t personally think it is cheap, sounds more like a great idea to me altho I’d probably go for the gusset for fit and also probably to show off.

  8. Dana says:

    Kathleen, blog topic idea. The production processes behind these made-to-measure/design-it-yourself business models. Can’t for the life of me figure out how someone is making money selling custom $77 jeans even if they are made in India. Would be really interesting to understand how these companies are set up to manage the pattern making, cutting, parts inventory, etc in this business model.

  9. Paul says:

    If my memory is correct, I think Kathleen had an entry about a denim business that actually makes the custom fit jeans in India. Part of the entry was by the person that operates the business.
    In the link above to denim quality Kathleen mentioned something about bifurcated butts.
    I am living and working in Dalian China and I saw a pair of jeans on a young lady today that had multiple seaming over the butt to give it a more rounded shape and it definitely worked. Also, high waisted (at the normal waistline) jeans seem to be making a come back here – it is about time. For those that truly like the low waisted styles, then you need to see what the Japanese are doing inspired by the Brazilians at http://www.sanna.jp (bikini jeans).

  10. Matthew Pius says:

    The NYT article on custom-made jeans reminds me of an earlier blog post where Kathleen posted some comments from a home sewer about her learning trajectory in learning to draft patterns. It sounds like the reporter, in ordering her jeans, was choosing measurements and proportions to try to create a specific “look”. It sounds to me like the end result was the sort of lesson that home sewers learn when they first try to make their own designs from scratch.

    There are certain proportions which are used in RTW based on either a lot of sizing research or on trial and error. But, if you haven’t made a lot of patterns, then you don’t know this. Specifically, she mentions that the fit of the jeans below the knees was way too tight, but it sounds like the author had specified a smaller circumference at the knees in conjunction with adding lycra to the fabric. Since she doesn’t know about the necessary proportions for calf/knee/thigh circumference in relation to leg length and waist/hip circumference, she didn’t realize what the result of her choices would be.

    Unfortunately, the author didn’t even know enough to make this next step in logic as to why her choices didn’t work (putting aside the issues of accuracy in measurement). This sort of site would be ideal for people with “nonstandard” body types who are educated enough to know how their needs differ from the industry’s “standard” measurements – assuming the quality of the resulting product is decent, which there seems to be some debate about.

  11. Nousher Ahmed says:

    Recently I have read a file titled RECOMMENDATIONS FOR THE PREVENTION OF LEG TWIST, prepared by fashion incubator.

    I faced some difficulties to understand some points of this file. I like to quote some sentences from page 4. Under the title BEST PRACTICES TO AVOID TWISTED LEGS it has been said, “Because of skew variation, we recommend that front leg panels and back leg panels be positioned on the marker so that they are not cut from the same quadrant for the same leg of a garment”. (Figure 2 shows four quadrants of a fabric). Can we conclude the following point from this sentence?

    Front leg panel and back leg panel of a same leg must be cut from different quadrants. As the fabric is divided into four equal quadrants along width wise, if front leg panel of a leg is cut from quadrant one, back leg panel of same leg must not be cut from the quadrant one but from any quadrant among quadrant two, three and four. That means, as front leg panel is from the quadrant one, if back leg panel is cut from the quadrant two, it is OK. If back leg panel is from the quadrant three, it is also OK. If back leg panel is from quadrant four, again it is OK. Please correct me if I am wrong.

    But the following sentence of above quoted sentence is: “Panels cut from quadrant one and quadrant four should never be sewn together”.
    That means if front/back leg panel for a leg is from quadrant one, back/front leg panel of same leg should never be from quadrant four. Either it will be cut from quadrant two or from quadrant three. Please correct me if I am wrong.

    So doesn’t the second line (Panels cut from quadrant one and quadrant four should never be sewn together) oppose its previous line (Because of skew variation, ……………. for the same leg of a garment)?

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