I love making seamless crochet stuff. It's great when I make the last stitch in my crochet item, and it's done. Joining can be such a pain. Since I can't find instructions anywhere (do you know of any?) that explain how to make something seamless, I'm going to publish the method I settled on after much trial and error. The following instructions are for single crochet.
Basic InstructionsRow 1 - Make a row of single crochet, slip stitch last single crochet to first single crochet, chain 1, turn clockwise.
Row 2 - single crochet in top of slip stitch, single crochet to end of row, slip stitch to first single crochet, chain 1, turn clockwise.
Row 3 - single crochet between the first and last stitches of the previous row, single crochet to end of row, slip stitch to first single crochet, chain 1, turn clockwise.
Repeat Row 3
Detailed instructions (text is above its corresponding photo)
1) Make a loop of single crochet stitches. In my example, I used the Happy Hooker magic ring technique on page 52 and made a circle of 19 stitches. I count the slip stitch as number 20.
2) Slip stitch the last stitch to the first stitch of the row, chain one.
3) Turn clockwise (indicated by red arrows above) and single crochet in the top of the slip stitch. Turning clockwise is important. I've tried everything I could think of, in all combinations ... clockwise, counterclockwise, turning differently every other row, doing the single crochet from the inside, wrapping the yarn in the front first ... turning the piece clockwise every row produces a consistent looking non-seam.
4) Single crochet to the end of the row for a total of 19 stitches. I know I'm at the end of my row when I see the vertical yarn from last row's turning chain.
5) The next two photos are a different crochet piece (I don't want to confuse you), but they are a good close-up example of what I mean when I say "vertical yarn from last row's turning chain." In the first picture, I'm on the second to the last stitch. In the second picture, I've made the last stitch. See the vertical yarn coming out of the next stitch? Don't' stitch in that one.
6)
Open the supplemental tutorial for images of this part of the process from the inside and outside of your item.
This step is: slip stitch, chain one, turn clockwise, deep single crochet in the space between the first and last stitch of the previous row.
I make this deep single crochet to even out the huge bump you get if you just make a normal single crochet.
7) The rest of the single crochet stitches in this row should be made as normal. Repeat step 6 and 7 until your item is done.
Here is what the non-seam looks like. The green parts show you what the slip stitch and turning chain look like as part of the fabric. If you don't always turn your piece clockwise, this part will look randomly uneven.