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.
It is 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. The first stitch in each pair will ultimately appear on the side of the work which faces you as you cast on, whilst the second stitch in each pair will appear on the opposite side of the work.
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. I found a video demonstrating this technique here. Note that the first cast-on stitch is created by whichever colour yarn is held over the forefinger and the second stitch is in the colour of the yarn held over the thumb. (As noted above, the first stitch in each pair determines which colour will appear on the side of the work facing you as you cast on, whilst the second stitch in each pair determines the colour which will appear on the other side.)
Two-colour Italian Cast-on (as used for brioche knitting): see link here.
There is a video by Knit Purl Hunter showing their version of this method in action: see link here. My Glass Island cowl on Knitty.com uses this method of cast-on. The stitch colours appearing on each side of the work are as described above for the long-tail method.
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.
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 or row. 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.
In this video, 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 need to 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 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. There are various videos available online showing how this is done by transferring alternate stitches onto separate needles before grafting. My preferred version is this one from Lucy Neatby 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 with yarn in front (using the appropriate yarn colour for the stitches appearing on the back of the work). Following this, a long tail of the other colour yarn is cut and, with the yarn needle, both sides are grafted together. This method ensures the number of rows/rounds on each side of the work remains equal. Lucy’s version involves working several set up rows using a single colour of yarn before performing the graft, however only the one set up row/round is required if the bind-off is being worked with two colours of yarn.
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
East London Knit – including an alternative method for casting on or binding off
double-knitting.com – with links to some video tutorials