Where to Put the Needle
Duplicate stitch is a knitting technique that allows you to cover stockinette stitch while making it look like the new stitches are part of the knitting. Most of the time people use this for adding details and colorwork patterns to a project, but you can also use it when weaving in ends.
As its name suggests, duplicate stitch creates a matching stitch over a knit stitch. When you use a contrasting color, it can look like fair isle knitting. The benefits of this method are that you don't have to plan ahead for your design and you don't have to carry yarn throughout a whole row. That's especially good for small designs!
Starting the Yarn for Duplicate Stitch
Use duplicate stitch on stockinette knitting. Grab a finished piece of work up a quick swatch to practice.
Thread a length of yarn through a tapestry needle, like you would when weaving in ends. On the back of your work, near where you want to add your stitches, weave through the back of several stitches to secure the end of the yarn.
Begin a Duplicate Stitch
Notice that stockinette is a series of little Vs. Depending on how you look at it, it may look like upside-down Vs, but it's best to look for the upright ones for this.
Come up through the knitting at the bottom of the first V stitch you want to work your duplicate stitch over.
Slide your needle behind the V that's right above the stitch you're covering.
Finish a Duplicate Stitch
Go back down at the bottom, in the same space where the needle came up.
Completed Duplicate Stitch
Try to keep the tension on the yarn snug so the stitch isn't too loose, but not so tight that it pulls at the existing knitting.
The stitch should cover the stitch underneath and if you need to adjust the placement, now's the time to do that. This can happen if the needle goes through just a little above or below where it should or if the new yarn overlaps itself in an odd way.
Working Rows of Duplicate Stitch
You can work rows of duplicate stitch in any direction. When working from right to left, insert the needle from right to left. When starting the next work going left to right, insert the needle left to right. For some designs, it may work out better to work from top to bottom or even diagonally.
Whatever path you follow, be sure to keep the yarn tension even. If you need to skip over an area that's larger than two stitches, weave the yarn through the back of a stitch or two so it doesn't snag or pull on the back.
When you finish your stitching, secure the end of the yarn on the back just like weaving in the ends as usual.
Tips for Duplicate Stitch
Because duplicate stitch adds another layer over your knitting, it makes the material bulkier and stiffer. Be sure to take that into account on your project.
Using the same weight yarn ensures that the stitches look more like they were part of the original project, but you can use different weights for more contrast.
For ideas to use with duplicate stitch, try simple fair isle charts, search for duplicate stitch charts (like this adorable apple pattern), or even work with basic cross stitch designs!