It's a lot of fun to collect vintage knitting patterns, but just as with modern knitting patterns and books, there's no real point in having the collection if you aren't going to use it.
But knitting a project from a vintage knitting pattern isn't as easy as knitting from a modern pattern that uses terminology and formatting that you understand, not to mention yarn that might still be on the market. Here are some things to think about and helpful hints for working with vintage knitting patterns.
Almost without exception the yarn used in whatever vintage knitting pattern you're looking at has probably long since been discontinued. Really old patterns don't even list brands or yardage -- a pattern in Weldon's Practical Knitter for a "Gentleman's Undervest" (really a sweater) simply calls for "6 ozs. of best white merino wool."
So how do you figure out how much of what weight of yarn you need? There's a lot of guesswork involved with those really old patterns. The suggested needle size can be helpful (more on that in a minute) in determining the proper yarn weight to use, and you can make an educated guess on the yardage by looking at modern patterns with similar shapes.
If you have a pattern that calls for a particular yarn, you may be able to find information about that yarn online. Vintage Knits has a great discontinued yarn chart that includes a lot of old yarns, with fiber content where available, weight in ounces and approximate yardage. So, for example, I have a vintage booklet of baby knits from Corticelli yarn, and while the particular yarns used in the patterns are not on this list, I see that the yarns that are listed for them were sold in one ounce balls that were around 167 yards. So a pattern that calls for 6 balls could be estimated to need around 1,000 yards of yarn (the pattern I'm looking at is for a little girl's dress, so that's probably quite the overestimation, in fact, but it's a start).
Where patterns are sometimes not very specific about the yardage or type of yarn used for the project, the good news is for the most part needle sizes are more specific. The only potential problem is knowing what size needle they're really talking about.
Going back to that girl's dress patter I was just talking about, it says you need one pair of size 11 12-inch knitting pins. But is size 11 the American, metric or British measurement?
If you guess wrong you'll see a very big difference in your knitting. Size 11 American is an 8 mm needle, which is smaller than an 11 mm needle (the equivalent of an American 17), but much bigger than a British 11, which translates to a 3 mm needle. There's no equivalent in US needles, but it's somewhere between a 2 and a 3.
Given that this is a kid's pattern with a photograph that shows me it was worked in a fine gauge yarn, I'm pretty sure this pattern means a British 11. Given that the yarn company that published the pattern book is Canadian, I'm even more assured that's the right choice. This pattern also helpfully has a gauge measurement (here called tension, again in the British style) of 8 stitches to the inch, so I could try a 2 or 3 mm knitting needle with my chosen super-fine yarn to see at what size I got the proper measurements.
Pattern Size and Fit
Where things get really difficult is knowing what size project you're knitting. Some really old patterns (looking at Weldon's again for example) there are no sizes given at all. Some patterns, such as those for children, might give you an age range (that dress I've been talking about is sized 2-3 years) but you should know that a "standard" size from back in the day is probably nothing like a standard size today.
Looking again at a great resource from Vintage Knits, we can easily see that the style in terms of fit has changed a lot through the years. A pattern from the 1920s, for example, would have been written to have a much more relaxed, less-fitted result than, say, one from the 1940s, when rationing required knits to fit closer to the body.
Vintage Knits notes that even number sizes through the years can't be trusted -- by bust measurement a 1950s size 14 is today's size 2!
The best thing you can do to determine size is to figure out the gauge used in the pattern, if possible, and do a little math based on how many stitches are cast on or worked at particular points in the pattern to see if it will fit. Or, if you're a process knitter, just cast on and see what happens; you're sure to learn something!
Have an Open, Patient Mind
Perhaps the most important tip for working with vintage knitting patterns is to be in the mood for adventure, experimentation and the potential for stunning failures when you work with old patterns. The less information in the pattern the harder it will be to reproduce, and many of the oldest knitting patterns are little more than descriptions of a process rather than actual knitting instructions.
It can take patience to decipher what a pattern is trying to tell you to do, and in some cases it's actually not possible to do exactly what the pattern says, so you have to be willing to experiment, interpret and possibly abandon or at least adapt a pattern that doesn't work for you as written.
If you ask me, that's the best possible thing about using vintage knitting patterns. Instead of trying to follow them verbatim, you almost get into a discussion with the original designer about how you might adapt her pattern to suit your needs. It's sure to make you more creative and adventurous as a knitter and teach you a lot about the history of this awesome craft.