Plaid is awesome and a plaid knit item is even awesomer. But the idea of carrying yarn across the back for miles and miles is not very appealing, and the tension on a single-stitch-wide vertical stripe would be very difficult to maintain. So how do we knit plaid? In my research, I found many different methods. I’ve put them in order of my favorites to my least favorite.
- Crochet Slip Stitch or Duplicate Stitch Vertical Lines. Knit horizontal rows of different colors for plaid stripes, simultaneously purling vertical rows where you want the vertical color lines to be. Then go back over it with the crochet hook, crocheting slip stitches of preferred color into the purl stitches. The knitted version that does not require a crochet hook is to duplicate stitch. This is my favorite method for single-stitch vertical lines. Example: http://blog.yarn.com/tuesdays-tip-easy-knitted-plaid/
- Slip Stitch Intarsia. Basically, for vertical lines, [k1 CC, k1 MC] and repeat until the vertical line is the desired width. If using more than one color, you may alternate with the three-plus colors as needed. This is ideal for multiple-stitch mixed-color vertical lines and/or vertical lines with a faded appearance. A variation of this is, if knitting a scarf, to knit it from side to side (that is, sideways along the long sides) rather than from end to end so as to reduce the number of color changes and intarsia yarn carry-overs. *CC = Contrast Color (the color of your stripes). MC = Main Color (the background color of your garment). Example: http://web.archive.org/web/20080830080545/http://www.diynetwork.com/diy/na_knitting/article/0,2025,DIY_14141_5311852,00.html
- Weave Vertical Lines. Knit horizontal rows of different colors for plaid stripes. When complete, weave long strands of yarn to create vertical stripes. A variation of this is to knit horizontal stripes and use YO’s (Row 1: k1, k2tog, yo, etc… Row 2: purl). When complete, weave a single strand of yarn through the YOs. This method results in tiny stripes and may make the fabric not appear knitted, which may or may not be desired. Example: http://www.knitty.com/ISSUEw13/FEATw13SIT.php
- Double-Knitting. In double-knitting, you basically knit a two-sided fabric simultaneously. When you knit a stitch, it becomes a stitch on the side you’re working; and when you purl a stitch, it becomes a stitch on the opposite side (where it appears as a knit stitch). It’s extremely easy to knit with two colors, wherein the pattern on one side is exactly reversed on the opposite side. It is not ideal for more than two colors, which is possible but difficult with double-knitting. Double-knit fabrics, by virtue of the fact that they are double-layered, are stiffer than single-layered fabrics, which may or may not be desired.
- Slip Stitch or Mosaic Knitting. In slip stitch knitting, a stitch may be slipped with yarn in front, wherein the yarn carried over the front of the stitch is visible on the finished product; these yarn-in-front lines create tiny horizontal stripes. Alternatively, you can use mosaic knitting, which is a type of slip stitch knitting. If you want a vertical stripe of a color from the horizontal row below, slip a stitch from the line below. This won’t create long vertical lines; usually, the stitch is only carried up one row, maybe two. The end product will be stiffer than without mosaic knitting and the vertical lines will be very short.
- Modular Knitting. Modular knitting, in which smaller pieces are knitted individually and either seamed or knitted onto the edges of other smaller pieces, may be adapted to create plaids. You can do it in such a way that it requires little or no seaming and very few ends to weave in, as in domino knitting. However, I still think this method creates far more work than it is worth. It might be fun to try it out for a single blanket square or a dishcloth, but not worth it in my opinion to use it in any other capacity.
- Argyles. Argyles are those diamonds you sometimes see on (mostly men’s) socks and sweaters, made famous way back in the 1800s. When knit with thin, intersecting lines across an entire fabric, they could essentially form diagonal plaid. However, the typical method of creating the thin lines found in argyles—which is the part you want to copy—is to duplicate stitch, as already suggested above. Furthermore, in the meantime, you’re knitting a ton of these tiny diamonds with lots of yarn ends to weave in, so you’re creating far more work for yourself than you need to. Furthermore, it would be far more difficult to adapt this method to, say, a shirt or sweater than almost any other method listed above. Finally, as stated above, argyles would form a diagonal plaid, which may not be desirable and would be much more easily done with any of the other methods listed above.