Knit and purl stitches
In securing the previous stitch in a wale, the next stitch can pass through the previous loop either from above or below. If the former, the stitch is denoted as a knit stitch or a plain stitch; if the latter, as a purl stitch. The two stitches are related in that a knit stitch seen from one side of the fabric appears as a purl stitch on the opposite side side.
The two kinds of stitches have a different visual effect; the knit stitches look like "V"'s stacked vertically, where as the purl stitches look like a wavy horizontal line across the fabric. Patterns and pictures can be developed in knitted fabrics by using knit and purl stitches as "pixels"; however, such pixels are most commonly rectangular, rather than square, depending on the gauge of the knitting. Individual stitches, or rows of stitches, can be made taller by drawing more yarn into the new loop (an elongated stitch), which is the basis for uneven knitting: a row of tall stitches may go back and forth with one or more rows of short stitches for an intriguing visual effect.
Short and tall stitches may also go back and forth within a row, forming a fish-like oval pattern. In the simplest knitted fabrics, all of the stitches are knit or purl; these fabrics are denoted as stockinette and reverse stockinette, respectively. Vertical stripes (ribbing) are possible by having alternating wales of knit and purl stitches; as an example, a usual value and selection is 2x2 ribbing, in which two wales of knit stitches are and then two wales of purl stitches, etc. Horizontal striping (welting) is also possible, by alternating rows of knit and purl stitches; the simplest of these is garter stitch, so called because its great elasticity made it well suited for garters. Checkerboard patterns (basketweave) are also possible, the smallest of which is known as seed stitch: the stitches go back and forth between knit and purl in every wale and along every row.
Fabrics in which the number of knit and purl stitches are not the same, such as stockinette, have a tendency to curl; by contrast, those in which knit and purl stitches are arranged symmetrically (such as ribbing, garter stitch or seed stitch) often lie flat and drape well. Wales of purl stitches have a tendency to recede, where as those of knit stitches often come forward. Therefore, the purl wales in ribbing often be invisible, ever since the near by knit wales come forward. On the other hand, rows of purl stitches often form an embossed ridge relative to a row of knit stitches. This is the basis of shadow knitting, in which the appearance of a knitted fabric changes when viewed from different directions.
Generally, a new stitch is passed through a single unsecured ("active") loop, thus lengthening that wale by one stitch. , this need not be so; the new loop can be passed through an already secured stitch lower down on the fabric, or even between secured stitches (a dip stitch). Depending on the distance between where the loop is drawn through the fabric and where it is knitted, dip stitches can produce a subtle stippling or long lines across the surface of the fabric, for example, the lower leaves of a flower. The new loop may also be passed between two stitches in the present row, thus clustering the intervening stitches; this approach is usually used to create a smocking effect in the fabric. The new loop may also be passed through two or more previous stitches, producing a decrease and merging wales together. The merged stitches need not be from the same row; as an example, a tuck can be formed by knitting stitches together from two different rows, producing a raised horizontal welt on the fabric.
Not every stitch in a row need be knitted; some can be left as is and knitted on a subsequent row. This is known as slip-stitch knitting.[6] The slipped stitches are naturally longer than the knitted ones. As an example, a stitch slipped for one row before knitting would be harshly two times as tall as its knitted counterparts. This can produce intriguing visual effects, even though the resulting fabric is more rigid, because the slipped stitch "pulls" on its neighbours and is less deformable. Slip-stitch knitting plays an crucial role in mosaic knitting, an crucial technique in hand-knitting patterned fabrics; mosaic-knit fabrics often be stiffer than patterned fabrics produced by other techniques such as Fair-Isle knitting.
In some cases, a stitch can be deliberately left unsecured by a new stitch and its wale allowed to disassemble. This is known as drop-stitch knitting, and produces a vertical ladder of see-through holes in the fabric, corresponding to where the wale had been.