The clamshell is a traditional stitch that rapidly bulks up to make oh-so-pretty blankets, cushions, and rugs.
Its rows of scallop-shaped patterns stand out best if you change yarn colors with every clam shell. Try it in a chunky yarn and you'll have a snuggly throw before you know it.
How to crochet the clamshell stitch video tutorial:
This tutorial, from creativeazngirl, explains how you need to start with a foundation chain in multiples of eight, with two stitches over. If you prefer a written tutorial, there's a great one available from Sandra at Cherry Heart.
Clamshell stitch written instructions:
Put simply, you need to single crochet into every chain for your first row. Then chain one, turn your work and single crochet into every stitch for your second row.
For row three, turn your work but do not chain. You will now slip stitch into the first two stitches. Then do a half double crochet into stitch number three. Double crochet into the next three stitches. The next stitch is a half double crochet. Then slip stitch the next three stitches. Then the pattern will repeat as you do a half double crochet in the next stitch, double crochet in the next three stitches, then a half double crochet and three slip stitches. Continue this pattern until the end of your row.
At this point, you should change the color of your yarn to get the best pattern contrast. You'll make your own choice but a bold contrast looks very effective. So attach your new yarn, chain three and turn your work. Double crochet into the next stitch (the chain three counts as a stitch), then half double crochet into the following one. Single crochet the next three stitches along. A half double crochet comes next. Miss out the next slip stitch, then below the following slip stitch put a double crochet. Then double crochet again right below your last double crochet. This makes the spike of the clamshell. Then double crochet into the next double crochet along, making sure your yarn does not cross at the back. Skip the next slip stitch, then half double crochet into the next stitch. Keep repeating this pattern until you are at the end of the row, which finishes with one double crochet into the two remaining stitches.
You are now onto your fifth row. Chain one and then single crochet into each stitch of the row. For row six, chain three, turn the work, double crochet in the first stitch, then a half double crochet, then slip stitch three stitches. Next you will do a half double crochet, then three double crochets, then a half double crochet, three slip stitches, and repeat the pattern along the row.
What can you create with the clamshell stitch?
You now have the basis of the pattern at your finger tips - what you create with it is your call.
There are plenty of gorgeous afghan patterns out there featuring the pretty clamshell stitch, but it would also look gorgeous as a pillow cover or a scarf. You'll be spoilt for choice.