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October 12, 2012 5:52 PM   Subscribe

How can I tell in advance if a knitted fabric will run when I cut it?

I want to make alterations to some clothes that are made of knitted fabrics like jersey or double-knit -- something like, say, shortening the sleeves. (I'm not talking about hand-knitted sweaters.)

Some knitted fabrics are just fine when cut, but others develop runs (a/k/a "ladders") from the raw edge. Is there a way I can determine ahead of time how a particular knit fabric will behave when I cut it? I'm imagining that, if I were to look at the stitches very closely under a magnifying glass, I might be able to tell, if I knew what to look for. Any clues what that might be?
posted by Corvid to Clothing, Beauty, & Fashion (4 answers total) 4 users marked this as a favorite
Jersey-knit fabric is just stockinette stitch, made on a machine with thread instead of yarn. The fabric is created row by row, with each stitch in the current row looping through the corresponding stitch in the previous row. Laddering happens when a stitch no longer has the next stitch above it to keep it in place, so it pulls into just a length of thread. Then the stitch below it no longer has anything to support it, etc. If you cut parallel to the rows, every stitch along the cut edge has this problem, so you'll get laddering; to avoid laddering, cut perpendicular to the rows.

In the first picture in the Wikipedia article, the rows go horizontally and each stitch is a little "v" shape. So, look closely at your fabric and orient it like the picture, then cut vertically. Bad news, though: the fabric in sleeves is usually oriented the wrong way to take advantage of this advice. You'll probably just have to make sure not to pull on it before you hem it.

p.s. Cutting hand-knit fabric when shaping a garment is a valid technique -- it's called steeking. It is terrifying, though.
posted by zeptoweasel at 6:16 PM on October 12, 2012 [4 favorites]

The cheater's way to do this - Superglue. Put a thin line of it marking your cut, then make sure NOT to cut past the line.
posted by pla at 6:19 PM on October 12, 2012 [3 favorites]

You can always sew your new seams/hems, then cut- then even if the edges begin to fray, they'll be stopped by your new hem-line.

This works even if you're not hemming- so long as your stitches are narrow enough to "entrap," as it were, most of the knitted stitches, once you've got a stitched line above where you're going to cut, you can cut without (too much) worry.

This second method- stitching, then cutting, knitted fabrics- is how I was taught to approach knits for machine-knitting. It's more work, but you don't lose fabric to fraying/laddering.
posted by Cracky at 6:56 PM on October 12, 2012 [2 favorites]

The sort of stockings that get runs will often get runs when cut. I've never had this issue with jersey. Don't stretch the fabric when cutting it, and be sure your scissors are sharp. Some people have better luck with rotary cutters.
posted by yohko at 8:50 PM on October 12, 2012

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