So, what's the big deal with intarsia in the round? Let's take a simple example and look at what happens. For our example, let's suppose we're knitting a blue hat, and we'd like to put a nice bright yellow smiley-face on the front of it; we'll use intarsia to make the big yellow circle, and then duplicate stitch the eyes and mouth in black later. So, on the first round where the smiley-face starts, we're knitting along with our blue yarn, and then we introduce a strand of yellow yarn and work those stitches, and then we'll use a second strand of blue on the other side of the smiley-face and complete the round -- and here's where we start to see a problem, because we've left our first blue strand over next to the yellow. We could continue knitting with the second blue strand, but that just compounds the issue, because then we'll have two blue strands next to the right edge of the smiley face -- but the yellow yarn is over on the left edge, and even if we dealt with that, what on Earth are we going to do when we get to the next blue segment?
The problem, as this makes pretty clear, is that when you're working in the round, you're always working from the right to the left vis-a-vis the face of the fabric, never left to right, but the normal method for intarsia requires you to leave your yarn at the left edge of each block. The challenge, then, is to get that yarn back over to the right edge somehow. There are several methods of doing this, and we'll go through a few and look at how they work.
Before we get started on that, though, let me note that one thing each of these methods has in common is that at some point you're going to be working counterclockwise (as viewed from the top) around your tube of knitting. This can be done by turning the work around, so you're knitting on the far side of the curve and looking at the inside of it, but this is also a good place to employ knitting back backwards, in which you work from left to right across the face of the fabric. In fact, knitting back backwards is a pretty good technique for intarsia even when you're working flat, because it lets you keep all the strands on the side away from you throughout the entire process, and that can simplify your yarn management considerably. If you're not familiar with this technique,let me direct you to this article on the topic, which I wrote for Knitty magazine. If you use this technique for intarsia, on the left-to-right rows you'll be bringing the new strands up from the left, not from the right, but if you just keep in mind that the object is to wrap the new strand around the old strand, I don't think you'll have any trouble keeping straight which way to go. Throughout this post, I'm going to refer to "working clockwise" when you're working in the normal direction in which you usually work a piece in the round, and "working counterclockwise" when you're working back the other way, whether you do it by turning, purling, and turning again, or by knitting back backwards.
The first technique we'll look at for knitting intarsia in the round is the "festive knitting" method, which is a semi-stranded method; as that implies, it's also useful for motifs that would lend themselves to stranding if they were used all the way around the item, when those motifs are used in an isolated location instead, and for that reason we'll be revisiting this technique again. This method was described by Mary Thomas in Mary Thomas's Knitting Book, and it's also used by Meg Swansen and Priscilla Gibson-Roberts in some of their books. In this method, the motif color is used only where the motif is and if you have two or more motifs they each get a separate strand, but the background color is stranded behind the motif and goes all the way around in a single strand.
We'll use our smiley-face hat to illustrate this method; we'll need one strand of yellow, and only one strand of blue since it will be stranded around behind the yellow motif. We'll begin on Round 1 by knitting with the blue yarn up to the right edge of the smiley face. Introduce the yellow yarn so it comes in from the right, and knit the smiley-face stitches, but strand the blue yarn along behind. At the left edge of the smiley, drop the yellow yarn, and continue with the blue yarn around. On round 2, knit with the blue yarn to the right edge of the smiley, then slip all the yellow stitches, stranding the blue yarn behind them. Twist the yarns together, and work counterclockwise across the yellow stitches; this gets the yarn back to the right edge of the smiley. Returning to working clockwise, slip the yellow stitches again, and continue with the round in the blue yarn. Repeat these two rounds until the motif is complete. It's very important with this method to keep the stranding of the background color loose; if it's too tight, it will make the design pucker. Also, if the strands are very long and seem likely to catch on things, you may wish to tack them down with the tail of the motif yarn before you weave it in; just use your tapestry needle to lightly catch the back of the motif stitches, allowing the yarn to go over the background-color strands and hold them in place, and then weave in as normal. I'll just note briefly here that I am assuming a solid motif in giving this explanation; we'll revisit this technique when we talk about stranded methods, to discuss what happens when you've got a mix of motif-color and background-color stitches within the motif.
The other two methods I'm going to discuss are essentially a disguised version of knitting flat, with joins made row by row. With each of these, you'll be working counterclockwise all the way around the piece on alternate rows. If you typically experience a change between your gauge flat and your gauge in the round, expect to experience it here; you may wish to swatch in both methods and possibly compensate by changing needle size for the intarsia section.
The first method uses a join within the background-color section, and is accomplished in much the same way as closing the gap in short rows. In fact, while I'm going to explain it using yarnovers, you could easily substitute any of the other short-row gap-closing methods if you prefer. Continuing with the example of the smiley-face hat, we'll want two strands of blue and one of yellow. The first round which includes the smiley will be worked just as if we were working intarsia flat -- knit up to the right edge of the smiley with the first blue strand, then work the smiley with the yellow strand, then work the remainder of the round with the second blue strand. At the end of the round, however, instead of continuing on clockwise on the next round, you'll do a yarnover, and work back counterclockwise with the second blue strand, then the yellow, then the first blue strand again. On the last stitch with the first blue strand, work that stitch together with the YO that was made with the second blue strand. For the next round, make a YO, and work around clockwise, and again work the last stitch with the second blue strand together with the YO made from the first blue strand. Continue in this manner, working clockwise and then counterclockwise on alternate rows, making a YO as the first stitch of each row and working the last stitch together with the YO. When you work these stitches together, you will want the YO to be the inside stitch of the two being decreased, so it's hidden and the join is unobtrusive; for the clockwise direction, you'll wish to do an SSK or other left-leaning decrease, and for the counterclockwise direction, you'll wish to do a p2tog (if purling on the inside) or KBB2tog (if knitting back backwards). At the top of the motif, if you are moving counterclockwise, finish your counterclockwise row, and then on the next clockwise row, do the YO and work the entire row in the background color to the last stitch; SSK that stitch with the YO, and then simply continue working clockwise in rounds; if you are working clockwise on the last row of the motif, you can simply keep going clockwise.
The other method makes the joins where two of the color blocks meet, and is done by linking one yarn around the other as with flat intarsia, but with some changes because the yarn to wrap around isn't on the correct side yet. It has the disadvantage of having a slightly higher potential for getting tangled up in your work, and the advantage of being quite seamless; I definitely prefer this method. We'll continue using our smiley-face hat example; we'll need one strand each of yellow and blue, because in a seamless hat, there is one section of each color. On the first row which contains the motif, you will work with the blue strand to the right edge of the motif, then twist the yarns as usual and work the motif with the yellow strand. Now, having reached the left edge of the motif, you need to wrap the yellow yarn and blue yarn together, but the blue yarn is still back over on the right edge. What you're going to do is bring the blue yarn all the way around counterclockwise in a very long strand, and lay it over the yellow yarn; don't worry about the length of this very long strand, because we're going to take care of it in a minute. Once you've laid the blue yarn over the yellow, work counterclockwise with the yellow until you're back on the right edge of the motif. Drop the yellow strand inside the loop of blue yarn that you created in the previous step, and then use that blue strand to continue working counterclockwise through the entire blue section; pull out slack from where the end of the strand is caught by the yellow as needed. When you've completed the blue section and are at the left edge of the yellow motif, pull the blue strand taut, so there's no more slack in it and it's snug up against the yellow section. At this point, the blue strand is at the left edge of the motif, and the yellow strand is at the right edge. Draw the yellow strand loosely across the back of the yellow section, and lay it over the blue strand, and then work clockwise with the blue strand until you're back to the right edge of the motif. Drop the blue strand through the loop of yellow, work the yellow stitches clockwise, and then pull the yellow strand taut. As you can see, you're essentially working flat, with the turning point at the left edge of the motif (a brief note: if you have more than one motif, as when you put a design on the front and another design on the back of an item, the join point will end up at the left edge of the last-worked motif), but the left edge of the motif and the right edge of the background section are being linked together in exactly the same way that the other edges are; this gives you an effectively seamless tube. At the top of the motif, if the last row of the motif was counterclockwise, the yellow yarn will be at the right edge; do not draw it across the back, but simply do a YO with the blue yarn and resume working clockwise in rounds, using SSK to work that YO together with the stitch before it on the next round. If the last row of the motif was clockwise, slip the motif stitches in the counterclockwise direction to get back to the right edge of the motif, and then simply pick up the blue strand and resume working clockwise in rounds.
These are by no means the only methods of working intarsia in the round. For instance, Lucia Liljegren has come up with a method of working seamless argyles (which are traditionally worked flat) by working each diamond individually with short-rowing (and she's currently working through a test-knit, if you'd like to follow along). This is very clever, and really exploits the way that intarsia consists of separate knitted blocks linked together only at their edges. I'm sure there are other methods out there; if you know of one, please share it!