Double knitting is literally knitting two back-to-back pieces of work simultaneously that you weave together as you knit. The result is a seamlessly reversible garment or fabric. Double knit mittens take advantage of the insulation value of trapped air, while allowing the knitter to back water resistant fibres with soft yarns that are kind to the hands. It also provides added opportunity to create two-color patterns by varying the sequencing of stitches when using the same type of fibre on both sides.
Place the hand of the future mitten wearer on a piece of paper with the thumb spread wide and the fingers together. Draw around hands. Be sure to make a pattern of each hand; our right and left hands are not perfectly symmetrical. Label the drawing right and left. Cut out the pattern pieces and save to check size and shape of the mittens. Make the mittens a little large for growing hands, allow for seams and movement in hands that are no longer growing.
Knit a sample square of knitting using two of the double point needles and the yarn you plan use to make the mittens. Measure the sample, and count the number of stitches per inch in both directions. Read the beginning part of the mitten pattern, and compare the recommended stitch count per inch. If there are too many stitches per inch, use a larger needle set; if there are too few, try a smaller needle. Matching the stitch count is important to making the correct size mitten.
Compare the size chart that comes with the knitting pattern to determine the correct number of stitches to cast onto the needles to create the size of mittens needed for the planned wearer if you were going to make the pattern using standard knitting. To make double-knit mittens you will double the number of stitches, casting on in first colour A and the colour B of your selected yarn, using first one to cast on a stitch, then the other. Alternatively, you can cast on by holding both strands of yarn together using them simultaneously, and counting the number recommended by the pattern. The second method gives less control of the placement of different colours.
Cap one end of one of the correctly sized double pointed needles using a plastic knitting cap. Cast on 1/3 of the stitches. Cap the other end of the needle, then cast another 1/3 of the stitches onto a second double-pointed needle, being sure to cap the ends so that the stitches don't slide off. Cast the rest of the stitches on a third needle. Cap the end. You will remove the caps from each needle point when you need to use it for knitting.
Remove the cap on the loose end of the first needle. Insert the point of the fourth double-pointed needle into the first stitch of colour A. Using the loose strand of colour A from the third needle, knit one stitch. Yarn over -- which means to move the yarn from one side of the needle holding the stitches by going over the top of the work to the other side -- to the front of the work with both strands of yarn. Purl one stitch using the strand of colour B in colour B. Alternatively, if you are making a jacquard pattern, use opposite colours instead of matching colours.
Follow pattern directions for increases and decreases to form the shape of the mitten, including shaping the thumb. However, when the pattern calls for increasing a row by one stitch, you will need to add two -- one in each colour, and decrease by two -- one in each colour, when decreasing. If the pattern includes creating a pattern, making the mittens double-knit will create a pair of reversible mittens, with the inverse pattern on the opposite side.
Knit an ordinary pair of mittens before trying to make a pair of double-knit mittens.