I have been working on some designs using double-knitting technique, to create a reversible colourwork fabric resulting in two layers of stockinette stitch back to back, but with the colours reversed. This technique produces a wonderfully smooth and even fabric compared with stranded colourwork, as there is no need to ‘float’ one yarn at the back of the work. I have found, however, that the gauge tends to be looser than in single-colour stockinette, or stranded colourwork, therefore it is often necessary to drop to a smaller needle size in order to keep the fabric sufficiently dense and even.
There are several ways of casting on to start a double-knitting project. Usually the cast-on alternates between two colours of yarn. There are a few examples below, taken from other blogs and from Youtube, showing some popular cast-on methods.
Two-colour cable cast-on: this method uses the basic cable cast-on method, but alternating between two colours of yarn. There are a few online videos which describe this method – here is one example. This is the method described in the instructions for my Burano Cowl pattern. It produces a nice firm edge, although stretchy enough for purposes of the cowl. In the cowl pattern I alternate the yarns back and forth, largely to prevent them getting twisted (see an alternative video here which describes the edging effect you get if you deliberately twist the yarns). In the ‘un-twisted’ method, it makes a difference, on one side of the knitting, which yarn is carried above and which one below, as shown in the photos below.
When knitting in the round, the edging above will actually appear on the right side of the work (assuming that is the side facing you for your first round, being the side formed by the knit stitches rather than the purl stitches) – see example below.
On the other side of the knitting there will be a ‘rope’ effect in alternating colours as shown in this photo:
Two-colour alternating long-tail cast-on
This cast-on method produces a neat but stretchy edge. There is a video by Sockmatician demonstrating this technique here.
Two-colour Italian Cast-on (as used for brioche knitting): see link here.
There is a video by Sockmatician showing his version of this method in action (called ‘Two-colour alternating invisible cast-on’): see link here. This video also shows how to perform the cast-on if you’re planning to use the ‘magic loop’ method of knitting in the round, with a circular needle much longer than the circumference of the knitted piece. This involves changing halfway through and casting on the remaining stitches on the opposite end of the circular needle. One of my forthcoming cowl patterns uses this method of cast-on, but when it is knitted in the round on a 40cm circular needle which is short enough not to require the magic-loop method, it is not necessary to change halfway through and all the stitches can be cast on in the same direction.
The methods above produce a cast-on edge where both sides of the fabric are joined together. It is possible also to cast-on in a method which keeps the two sides separated (see, for example, this link from Arne & Carlos). In that case, the two sides of the fabric will only become interlocked once the colours are reversed as the colourwork pattern develops.
Finally, its worth noting that the number of stitches to be cast on is double the number of stitches which you want to see on each side of the fabric, this is because each pair of stitches represents one stitch on the front of the work and one on the back.
So how is double-knitting actually done?
The technique involves working pairs of stitches in two colours. Holding both strands of yarn behind the work, the first stitch in each pair is worked as a knit stitch using one colour. Both strands are brought to the front of the work and the second stitch is worked as purl stitch using the second colour. The purl stitch effectively acts as a ‘knit’ stitch on the reverse side of the fabric so that the reverse side looks like stockinette stitch. It is important to remember to bring both yarns back and forth when changing between knit and purl in order to prevent any strands of yarn from being carried across the outside of the work.
A charted pattern typically only shows the front side of the work – for each stitch shown it is therefore necessary to knit that stitch in the given colour then immediately work a purl stitch in the other colour used for that round. The other side of the work will therefore produce the same pattern in mirror image with the colours reversed.
Holding both yarns in one hand, or one in each hand, is a matter of personal preference. If holding in one hand, it is useful to alternate the direction in which yarns are swapped to avoid the yarns becoming twisted. There is a link to a Youtube video here which shows double-knitting performed holding both yarns in one hand, and another one here showing the two-handed technique.
In the first of these two videos, the technique is used to produce a flat piece of work. The differences to note, as compared with knitting in the round, is that the initial slip knot is dropped from the needle (and subsequently undone) when knitting in the round, whereas this does not necessarily happen when knitting flat. The technique used for flat knitting in the video above shows the last two stitches of every row being purled together with both strands of yarn, and then slipped at the start of the next row. This keeps the edges joined together and neat. Other methods exist (eg twisting the yarns together) for keeping the edges of the work joined.
In my Burano Cowl, I use a standard bind-off method (see example here) alternating between knitting the first stitch of each pair in one colour and purling the second stitch in the second colour. This gives a firm edge, although I found it can be quite tight therefore a conscious effort may have to be made to keep the bind-off loose. Alternative bind-off methods do exist. I experimented with some of the more flexible bind-off methods used in conventional knitting but found they caused the edge of the cowl to ripple rather than maintaining a neat straight edge therefore not all bind-off methods are necessarily appropriate for double-knitting.
When using the two-colour Italian cast-on noted above, a very nice matching invisible bind-off can be produced by grafting using Kitchener stitch. This it not as difficult as it sounds and there is a very helpful video here which shows how to do this using a single knitting needle and a yarn needle. The method involves working a set-up round, where the first in each pair of stitches is slipped (with yarn at the back) then the second in each pair is purled. Following this, a long tail of yarn is cut and, with the yarn needle, both sides are grafted together.
There are more complex techniques which can be applied to double-knitting (eg increases and decreases) which are beyond the scope of this blog post. In the meantime, here are a few other links to double-knitting online resources:
Wikepedia – for a few historical references to the technique
Twist Collective – including comments about knitting different patterns on each side of the fabric
East London Knit – including an alternative method for casting on or binding off
double-knitting.com – with links to some video tutorials