Elastic Cast On

The elastic cast on (aka German twisted cast on) is a variation on the long tail cast on, which I explain here. The elastic cast on is achieved by a simple variation, but the results are stretchier than the traditional long tail cast on, making it great for top down socks, hats, mittens, or anything requiring elasticity without comprising appearance or sturdiness. This the cast on I generally use for all my sock and hat patterns, unless I want a more decorate edge such as Channel Island or picot. 

Part 1

To start, you must determine approximately how long of a tail you will need to start your project. There are multiple ways to calculate tail length for this cast on; however, the most common (and usually most accurate) is to create a yarn tail roughly 3.25 times the size of your finished project, plus an extra 6 inches (15.2cm) for the remaining tail. As an example, if you are staring a scarf measuring 10" (25cm) long, you would make a tail that is 10"x3.25+6"=38.5" (or 25cmx3.25+15.2cm=97.8cm). Another common variation is to add together 0.5"-1" (1cm-2.5cm) for each of the cast on stitches (i.e. approximately 20" or 50cm for a cast on of 20 stitches) along with 6" or 15.2cm of extra for the remaining tail. You would calculate more stitches per inch or per centimeter for heavier weights and less for lighter weights.
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The most difficult part of the elastic (and long tail) cast on is determining how much yarn to start with. It is better to overestimate, as extra tail can be reduced later with scissors. If there is not enough tail to finish the cast on, and obtain the required number of stitches, you will have to start over. This is about the only complaint I have about the long tail cast on; apart from this, it is a good technique to learn.

Once you determine a measurement, create a slip knot at the end of this length. Place the slip knot onto the needle. Hold the needle in your right hand. Arrange the working yarn (the part attached to the ball) over your index finger and the tail length over your thumb, as shown below. You will now begin the rest of the elastic cast on, as explained in Part 2. ​

Part 2

Guide the tip of the needle over the back tail yarn (the part in back of your thumb, furthest away from from you). 

Wrap the needle tip counterclockwise around the working yarn.

Bring the needle tip through the loop on your thumb, between both the front and back strands, then carefully drop the tail yarn off your finger. ​

Pull the tail and the working yarn gently to adjust the tension of the stitches. They should be consistent and taut, but not overly tight. As a rule, you should be able to slide the stitches up and down the needle without any trouble but without the process being too easy. A cast on that is too tight or too loose is not only unsightly but will likely cause problems when finishing your project later.

Repeat the steps of Part 2 until you have the required number of stitches. Note that you will only be adding one stitch each time, as you will not be adding more slip stitches, only stitches created from the looping process shown in Part 2. Also to note, the starting slip stitch does count as the first stitch. It is worth pointing out that unlike with many other cast on methods, the tail hangs from the last stitch created, and not the first, as you can see below. This does not make a significant difference when knitting.

Once the cast on is complete, proceed with your pattern; there are no additional steps required to secure the elastic cast on before knitting your fabric.

Further Comparison of the Elastic and Long Tail Cast Ons

The physical difference between the two cast on methods is subtle, but if you look closely, you will notice the elastic cast on (orange yarn) has an extra layer of bumps along the cast on edge compared to the long tail cast on (pink yarn). This is because the elastic cast on uses both loops of the thumb wrap instead of only the front loop, as is the cast with the long tail cast on, resulting in a single ridge for its cast on edge. Keep this in mind when working both cast on methods, that way you are aware of which you are supposed to be working, as it is surprisingly easy to confuse them.
Of course, the elastic cast on is stretchier than the long tail cast on, as I mentioned previously. Besides this, there are no other differences, as they are essentially the same cast on done in different variations.

I hope you enjoyed this tutorial. If you have any questions about the topic shown here, feel free to post in the comment section section of this tutorial. Until next time, happy knitting!