One of the most helpful skills to know in knitting, yet seemingly one of the most mystifying and terrifying: substituting yarns in a commercial pattern. Allow me to be your guide into the hellish circles of gauge, fiber characteristics, yardage calculations and other abominations too appalling to mention here, lest you be scared away. Quick, throw a silver coin at Charon and climb in the Go Knit In Your Hat boat.
Step 1: Preliminary Research
We begin in a slightly counterintuitive place: we are going to study the yarn that is specified in the pattern, i.e., the yarn you do not want to use. Don't be put off by the sense that you are lingering in no-man's-land, like the poor souls in limbo; before you can pick a yarn that's even better, you must first know everything you can about the yarn you are rejecting (sounds kind of like dating, eh?).
Get a piece of paper. At the top, write down the gauge (sometimes called "tension") that the pattern uses. It will probably be listed over four inches (e.g., 18 sts over 4 in/10 cm), so divide by four and write this down, too (e.g. 4.5 sts per inch). This is the gauge that the pattern uses, and therefore the gauge that you must get, too.
Next jot down the name of the yarn used in the pattern and its manufacturer (I'm going to refer to this as the "specified yarn"). Write down, as well, the number of balls the pattern requires for the size you want to make. If the pattern uses more than one yarn, write them all down; if the pattern uses more than one color of yarn, write all of them down too, including color name and number if they are given.
Now, my dear friends, you must hop on over to Google, the internet user's best friend, and type in the name of the specified yarn, gently clicking on "Google Search" when you have finished. Find out as much as you can about this yarn. Yarn review websites like Wise Needle can be especially helpful here; also, many yarn manufacturers have their own websites which list their current yarns and give some basic information about them. You want to find out at least the following:
* recommended gauge (very important. Hear me? VERY IMPORTANT.)
* recommended needle size
* fiber content (cotton? wool? modal? recycled kitchen sponges?)
* percentage of fibers (75% wool/25% nylon? 100% cotton?)
* how many yards or meters in a skein, and what the skein weighs (grams or ounces)
* whether the yarn is shiny or matte, or has different plies of each
* whether the yarn is textured at all (boucle? tweed with nubbies? novelty yarn with eyelashes? thick and thin?)
* whether the yarn is a single color or not (tweed flecks? marled like a barber pole? plies that change color like some Noros? self-striping? self-patterning like sock yarn? variegated? gradual color changes in large blocks like Odyssey?)
any other special characteristics about the yarn (homespun texture? tight twist? cable construction?)
* any special washing considerations (machine wash? dry clean only? if water touches it, it will distintegrate?)
Hoo-boy, that's a lot of stuff.
Step 2: Examining Your Motivation
Now that you've gotten a pretty comprehensive description of the yarn specified in the pattern, I want you to think about why you've decided to substitute yarns. You must have some idea about why you're rejecting the specified yarn and what you might be looking for in a substitute. The answer might be as simple as cost: a sweater that requires, say, 10 skeins of Colinette Enigma at $26 a skein, may be a prime candidate for substitution with a less expensive yarn. Other reasons:
* the specified yarn doesn't come in a color or colors that you like
* you are allergic or sensitive to one of the fibers in the specified yarn
* you can't readily get the specified yarn
* you aren't familiar with the specified yarn and don't want to invest in sweater quantity of an unknown yarn
* the specified yarn has been discontinued
* the fiber is inappropriate for your needs (e.g. cashmere when you live in Hawaii)
* you don't like something about the look of the fiber but you like the pattern
* you've had a bad experience with the specified yarn or its manufacturer
* you want machine washability
* you don't think it's soft enough
* you hate the color combination shown
I could go on and on, but this list is, all by itself, a compelling argument for why you ought to learn how to substitute yarns well: it allows you to use a pattern you like while tweaking it to better suit your needs or aesthetic sensibilities.
Step 3: Guiding characteristics
Now it's time to flip that piece of paper over and start a list of what you are going to be looking for in your new yarn.
At the top of that list is the gauge measurement for your pattern. Yep, the same one that you wrote at the top of the other side of the paper. Now take a quick look at the recommended gauge for the pattern's specified yarn. Are they the same? If so, good. If not, write down the recommended gauge, too. I'm going to talk about these in greater detail later, since they're probably the single most important factor in guiding your choices.
Under your gauge notes, make a list of the characteristics you know you want the new yarn to have. Step 2 should have jogged your memory about what's important to you. Some of these are going to be easy to determine: you'll know if machine washability is a must or if you can live with hand-washing. You probably will have a clear sense of what your budget is for this particular project. You'll know if you want a particular color or fiber, or, just as important, if you don't want a particular color or fiber. Even if you haven't committed to a specific fiber or blend, you'll at least know whether this is supposed to be a winter sweater for a cold climate or a lighter sweater for summer, or a trans-seasonal kind of thing, and you'll know if you hate working with a particular fiber (e.g., cotton can kill some people's hands) or if you are allergic or sensitive to something (some people find even the nicest mohair too itchy).
At this point, revisit your pattern and take a hard, analytical look at the way the designer uses the fibers. Think about the specific characteristics of particular fibers and how they are used in the design. A pattern with a lot of texture and cabling may be knit in a yarn that shows good stitch definition; write this down. A soft jacket with lots of flow and loose tailoring is going to use a yarn that has good draping qualities. Write down "drape."
Don't forget to take a moment to second-guess the designer on the yarn choice. Let me share a dirty little secret with you: you can't assume that the designer picked the specific yarn shown in the magazine because (s)he loved it and it was an integral part of the design. It is quite possible, nay, even probable, that the designer swatched some completely different yarn or fiber, maybe something really, really different (like fuzzy bulky acrylic instead of fingering-weight silk tape) and -- brace yourselves -- the magazine's editorial staff asked her to change the yarn to the one shown because that yarn manufacturer (gulp) advertises a lot in the magazine. Or that Yarn Manufacturer A was providing free yarn for the book and so unless the designer wanted to buy the yarn herself out of pocket, she pretty much had to go with something Yarn Manufacturer A made. Or that the original yarn she did the swatch in was perfect -- but, alas, was discontinued before the pattern went to press.
Indeed, one of the reasons you may want to substitute in a particular pattern is because the fiber or yarn shown is impractical or unsuitable, and was chosen for some other, non-knitting related reason. I'm thinking of a sleeveless, hooded top with a cable pattern I recently critiqued in this very blog, knit in chunky-weight alpaca; for me, the yarn choice was a nonstarter, since a bulky alpaca, made even thicker by cables, with a heavy and warm hood, but no sleeves, just didn't seem sensible to me. If you wear it alone, the back of your neck (where the hood lies) sweats, while your arms have goose-bumps; if you want to layer it under a jacket, you look like a quarterback and have great difficulty moving your arms.
When doing a reality test with the pattern, think about the inherent characteristics of the fibers or yarns used. Alpaca and silk are notorious for their lack of elasticity. All-cotton yarns often sag out after wearing and a full-sized adult sweater can quickly start to feel awfully heavy; add a highly textured pattern or oodles of cables and the garment may feel like a suit of chain mail when you wear it. Cashmere socks are luxuriously soft, yes, but they will wear, pill, felt so very quickly.
This is also the time to make sure the designer isn't using the yarn(s) in an atypical way. And this is why I've asked you to double-check the gauge stated in the pattern with the recommended gauge for the specified yarn. Every once in a while, a designer will purposely knit a yarn at a gauge that is much heavier or much lighter than is typical for that yarn; to get the same effect, you'll need to compensate for this. Think about a lacey shawl knit in a worsted weight yarn. Worsted weight yarns usually knit at around 5 sts per inch. But the gauge stated for worsted weight yarn for this particular pattern is 3.5 sts per inch. If you were looking just at gauge, you'd see 3.5 sts per inch and think "I need a chunky yarn." No, you need a worsted weight yarn; you just need to knit it at a looser gauge, i.e., on larger needles than is typical for that yarn in order to get the loose, lacey, drapey shawl shown in the photo. To give another example of this important consideration, think about socks. Often sock patterns knit the specified yarn at a tighter gauge than usual to make them wear longer. For instance, a yarn that ordinarily knits at 5.5 sts to the inch may be knit at 7 sts to an inch to increase its sturdiness. That means that if you are making this pattern, you'll want to substitute a DK yarn (i.e. one that typically knits at 5.5 sts to an inch) and not a fingering weight yarn (i.e. one that typically knits at 7 sts to an inch) to get the same look and wear.
This is why it's so important to compare the manufacturer's recommendation for typical gauge, with what the designer intends in this particular pattern, and note any discrepancies. When there are differences, you'll likely want to go with a yarn that knits at a similar recommended gauge. You'll adjust needle size in order to tweak the gauge.
The same principle is going to apply in cases where the designer specifies holding two strands of yarn together. You'll want to consider each strand of yarn separately to make sure you match gauge and style if you want to match the effect the designer achieves. Again, go back to the information you found in Step 1 and figure out what each individual yarn is like; then figure out how to substitute for each.
Finally, remember that different stitch patterns are going to add or subtract from your gauge. The gold standard for substituting is stockinette stitch, but if the pattern you want to make isn't in stockinette stitch, your gauge may be affected. Ribs draw in (think of the top of a sock); you'll have more stitches crowded in per inch than if you knit in stockinette. Yarn-overs make holes and therefore expand your fabric; you'll end up with fewer stitches per inch in a pattern that uses lots of yarn-overs. A good knitting reference book can help you with this, but for purposes of substitution, you'll be safer considering the recommended stockinette gauge for the yarns in question.
Another quirky thing to look for are adjustments for shrinkage: Denim yarns, like Rowan's, shrink appreciably in the first wash and patterns for denim are, accordingly, written about 20% longer than the finished garment will be. If you try to substitute a yarn that doesn't shrink like that, you'll have a sweater that's 20% too long. Other yarns, like linen and hemp, are very stiff and rough in the knitting, but soften appreciably with each wash. You'll want to think about whether the garment shown in the photo shoot is one that some poor editorial assistant had to wash fifty times to get soft and broken in, the way it looks in the magazine. Some yarns fade with washing, again, Rowan Denim comes to mind. Consider whether a stonewashed look is going to work for you, or if you'll feel cheated if your sweater turns out fading in some spots as time goes by.
Next: Finding a good substitute, part deux
1) This is probably a good time to recommend to you Candace Eisner Strick's Beyond Wool. This book has some excellent information about fibers -- you guessed it -- other than wool, and their characteristics: which ones stretch, which ones drape, which are really warm, and so on. If you analyze her designs, you can see how she tries to compensate or highlight the relative disadvantages or merits of each fiber. It's a very educational book, and worth a read if you don't know that much about specific fibers.