Fair Isle knitting, also known as stranded knitting, refers to color work that is a repeating pattern worked over a group of stitches and rows.
Fair Isle differs from intarsia in that the nonworking yarn is carried across the wrong side of the work in strands called floats. It is important not to pull the floats too tightly or the knitted fabric will pucker, and this cannot be fixed.
The best way to control the tension of the floats is to designate one color as the over color, the other as the under color. As the knitting changes from one color to the other, the over strand will be held to the top on the wrong side of the work, the under strand will be held to the bottom.
Floats should never travel for more than three or four stitches, so you must compensate for them in one of the following ways. One method is to twist the strands of yarn together every three or four stitches by crossing them. This causes a twist in the yarns, which can be untwisted by crossing the strands in the opposite direction later. A second method is the Melville lift. Allow a long float to hang in the working row, but in the following row, lift the float over the right needle and work the stitch 'under' the float. Make sure the float is to the back of the yarn as the row continues. This catches the float and makes a decorative pattern on the wrong side of the work.
It is important to bring both strands of yarn over to the last stitch to prevent distortion of edge stitches, which occurs when the edge stitches are worked with no yarn stranded behind them. A useful way to do this is to add a selvedge stitch to each edge of the color work section, then work these selvedge stitches as follows: at the beginning of every stranded section, slip the first stitch.