For example: You would never use the same pattern stitch for a bulky jacket and/or a lightweight cardigan. The texture of the yarn in relation to the pattern stitch is also important; pattern stitches for hairy, looped, slubbed, or tweed yarns tend to be simpler than pattern stitches for the smooth yarns. In general, it is advisable to use the yarn called for in the directions when possible.
If you want to substitute a yarn choose one as similar as possible to the specified yarn. Be sure you can work to the proper gauge in the substitute yarn. If your gauge is not correct, the garment will be too big or too small. Be sure you like the texture of the pattern stitch in the new yarn. It may be too limp or too stiff even though the gauge is correct.
Yarns have different degrees of elasticity depending upon the fiber content. Care should be taken in substituting cotton or linen for wool as these fibers have less elasticity and additional stitches are needed.
Generally, the thicker a yarn is the less yardage it has per ounce and the more ounces it takes to cover the same area. That is why more ounces of bulky yarn are required to make a sweater than ounces of finer yarn. If you wish to substitute a thicker yarn than the pattern calls for, even though you can work to the stitch gauge, you will need more ounces of yarn. Yarns of the same type, thickness and fiber content have approximately the same yardage per ounce. In interchanging these yarns, the same number of ounces is usually required.
I usually just feel the texture and thickness of the wool that I wish to substitute the original wool for. I keep in mind what type of garment I am home crocheting and take it from there. You may not be able to do this until you have experience with yarns and patterns.
If you feel confident enough to go by the feel of the yarn, please keep in mind that you may have to work on the gauge. It is at this point that I usually purchase 1 or 2 balls of yarn extra – if you are fortunate enough to try to get the correct gauge immediately, you should have a general idea of how much yarn to purchase.
Keep in mind that dye lots on yarn or cotton change on a regular basis so time is of the essence.
If you choose to make a garment in an entirely different weight of yarn, this is, in effect, a new design. The design should be re-planned and the directions rewritten to the new stitch gauge.
With only the basic pattern and design of the garment in mind, it is not that hard to rewrite a pattern to suit your own type of yarn.
I have done this type of activity quite often when home crocheting and am usually pleased with the results.
Are you willing to try substituting yarns in your favourite home crochet patterns?