As a follow up to my talk in May about Successful Yarn Substitution, I thought it would be interesting to consider in more depth the situation in which you decide to use a yarn that is completely different than the one called for in a pattern - i.e., the wrong yarn. What does this mean exactly?
I addressed part A, above, pretty extensively in Part 1 of our yarn substitution discussion, so I'll only touch on it here. This sort of substitution is what I refer to as a heterogeneous substitution. You want to swatch it very carefully, not just to get gauge and calculate your finished measurements, but also to see what the fibre change will do to the fabric and therefore drape and fit of the project. Changing fibre-type will affect the weight and elasticity of the fabric and will give a very different finished product.
Part B is what I'd like to focus on chiefly here. This situation is assuming that you’re not radically changing the fibre characteristics of your yarn, but rather just changing the thickness or weight. Which is where the math comes in.
But first, let's give a little attention to my favourite topic: swatching. As everyone knows, I really like to talk about swatching. Obviously it comes up a lot for me, and I know not everyone loves it as I do, but it's pretty essential if you're going to pull off the operation we're about to address - changing gauge.
The reason I ask "How do you swatch?" is because in my experience each person has her or his own preferred method, and you can find as many "right ways" to do it as there are knitting experts. Every swatcher has a way they have worked out that they find successful, just as individual as each knitter's tension. Here are a few examples:
- Amy Herzog's Practical Tips on Swatching
- VeryPink Knits' Stellar Swatching (video)
- Clara Parkes' The Swatcher's Manifesto
- Brooklyn Tweed's Swatching 101
I'm not going to outline how I swatch - as evidenced above it's been done many times before. Start swatching, pick a method as a jumping off point and make it your own over time. Find what works for you and your knitting. What I will suggest is what I've pointed out in the slide above: that how you swatch should be dictated by what information you're trying to get out of the swatch. I don't just swatch for gauge. I also swatch to test shaping, to test fabric, to test stitch patterns, to test the yarn. And for each of these situations the swatch will have a different approach. I guess what I'm trying to get at is that, although knitwear designers and many knitters are rather militant about the need to swatch, the rules around how you must swatch are much more fluid and forgiving. The important thing is that you actually do it!
If you're just starting out on your swatching journey, however, here are a few quick guidelines for swatching specifically for guage: Make it big enough. This means big enough that you can get a good long average measurement from it (since most guages are based on a 4x4" square, you should make your swatch bigger than this!). Imitate the conditions under which your project will be made. Use the needles you're planning to make your project with. Don't swatch while watching a horror movie unless you're going to make your whole sweater while watching nothing but horror movies (this is a joke... sort of). Finish the swatch the way you'll finish and care for your project. If it's a sweater, you're likely going to wash it, so wash the swatch. If it's a hat and you're not likely to get it dirty, block the swatch how you plan to block the hat. If you need guidelines on how to measure accurately, use the links above.
Now that I'm done browbeating everyone about swatching (for now), let's move on to the examples. I thought the best way to talk about how to change gauge or yarn weights in a pattern is to create different examples of how you would go about it for an actual project.
Assumption: I should note here that I am making the assumption that in each of these examples, the needle size would also be adjusted to create appropriate fabric for the project. So for example, going from an Aran weight yarn to a Fingering weight yarn, you would not still knit the lighter yarn with 6 mm needles, but would instead size down to 4 or 3.5 mm so that you weren't left with a fabric of net-like gaping holes.
The first example is a straightforward scarf pattern that is free from Purl Soho. Below you'll find the original pattern information pertinent to changing the pattern.
Given this information, and the simplicity of the pattern, you have three options for changing the pattern depending on your chosen yarn:
Here are two examples of how you might change the pattern, Option 1 and Option 3:
In Option 1, you would maintain the CO count of the original pattern. At the new gauge with lighter yarn, the scarf will be only 6" wide instead of 10". If you were to use a heavier yarn, the scarf would turn out wider.
In Option 3, you would use the new gauge to calculate a new CO number to maintain the original width. To keep the width at 10" with the lighter yarn, you would cast on 70 sts instead of 42. If you were using heavier yarn and maintaining 10" as the width, you would calculate a smaller CO number.
For the second example, I used my Diamond Kerchief Cowl pattern as an example of converting a pattern where you have to take a large repeated stitch pattern into account. This is a conversion I actually did myself when I wrote the pattern for KnitPicks. The original sample I had made was in Fingering weight Fleece Artist yarn, but when I pitched the pattern I changed it to a worsted weight cowl. Here is the conversion I made:
Above are the pertinent details pulled from the pattern that you need to consider when making this sort of alteration. The more complicated the pattern, the more information you have to pull from the pattern to make your conversion, so try to think about the switch you're making from every angle of the finished piece.
This is an Option 2 conversion. At my new gauge, my aim is to maintain the circumference of the cowl, but I also have to take into consideration the stitch pattern repeat. In order to maintain a full repeat, I have to remove one full pattern repeat from the final stitch count, taking the count from 120 sts down to 100, which at the new gauge actually loses a couple of inches of the circumference and reduces it to 22". However, if I'd kept the 120 st count with that 6th pattern repeat, the circumference would have ballooned to 27" which would adversely affect the drape of the neck of the cowl.
In the next example, rather than an overall stitch pattern, this pattern (my Comforati Hat pattern) has a central stitch motif, and the stitches on either side of the motif are scaleable depending on the gauge of the yarn used.
Above is the information from the original pattern. For this conversion we'll be considering Option 3.
To convert the hat to a lighter yarn, you would add the extra stitches to the stitch pattern on the sides of the central motif. Above is the new gauge and the required stitch count to maintain the hat's circumference.
Figure out how to place the motif. For this hat, the motif is on each side of the hat, so the stitches remaining from the new stitch count is 34. This doesn't divide into an even number for the 2-st repeat of the border stitches, so it must increase to accommodate that, which gives a new overall CO number of 132 sts. The final step is to make sure that 132 will work with the 2x2 rib pattern of the hat's brim (you don't want 2 knit stitches to bump up against 2 other knit stitches at the join).
Finally, we'll consider a more complicated project. This is the Rocky Coast Cardigan by Hanna Fettig, and I converted it for myself with a sweater's worth of Cascade 22o. Let's take a look.
Originally the pattern is written for Aran weight yarn and 6.5 mm needles. With my Cascade 220, the 6.5 mm needles would result in a rather gaping fabric. I didn't want to use more than 5.5 mm needle with my yarn, so to the calculation pad I go!
Above is the new gauge I got by swatching my yarn on 5.5 mm needles and washing the swatch as I would my sweater.
Because I need the measurements for the 40" size, I used the old gauge and the stitch and row counts from the pattern for that size to calculate the final sweater measurements for body and sleeve length, shoulder width, arm circumference, etc.
With those measurements and my new gauge, I calculated how many stitches I would need to approximate the same measurements for my size. I then compared those stitch counts to the other sizes and found they were closely matched by the 55" size. I paid special attention to widths in this comparison, because the lengths are more easily dictated by my fitting preference as I knit the garment. So for the knitting, I am following the instructions for the 55" size instead.
When you're deciding if a pattern like this will work for a gauge conversion, consider the above criteria. These characteristics made it possible and straightforward for me to use a lighter yarn.
I hope you've found this helpful! If you have any other suggestions for successful yarn substitutions, please let me know - I'm always collecting good tidbits!