Blocking is a method of stretching and shaping a finished knitted piece to reach the desired dimensions in a pattern or to make your stitches look nicer and more even. Lace almost always requires blocking to open up the design so all of the holes and patterns show in their true glory.
There are three main methods of blocking: wet, steam and spray.
Wet blocking is the recommended method for blocking man-made fibers (i.e., polyester, rayon), novelty yarns (except for some that are very delicate and may fall apart when wet—please check the label for care instructions and do not wet anything that says it shouldn’t be wet) and some wool and wool blends if done carefully (remember heat and agitation can cause wool to felt).
Dampen the knitted piece so that it is wet (gently squeeze, do not wring out, the excess water). Spread the piece out on a blocking mat. If you do not have a blocking mat, as an alternative, place your knits on a sheet or clean garbage bag (the bag won’t absorb water, allowing the piece to dry faster) on the floor or a spare bed where it can sit undisturbed long enough to dry.
Gently stretch the piece as needed. If you’re trying to get a piece to the size or shape the pattern recommended, you might need a ruler, tape measure or yard stick to help you out.
Use rust-proof safety pins, straight pins or T-pins to hold the knits in the desired dimensions and allow it to dry, usually over several days. As the piece dries, it will retain the shape that you gave it.
Steam blocking is a similar to wet blocking, only you use steam to relax the fibers instead of water. This method is best for fibers that shouldn’t get wet such as cotton, which tends to lose its shape when wet. It shouldn’t be used on man-made fibers, because the heat and steam will melt them.
To steam block, simply pin the pieces out to desired dimensions, wrong side up. Wet an old sheet or pillowcase & wring out so it’s damp. Using a hot iron, press lightly down on the pillowcase, forcing steam through the fabric. Continue until the pillowcase is dry.
Alternately, you can skip the pillowcase and set your iron to a steam setting. Float the iron over the surface of the knitted piece WITHOUT TOUCHING, forcing the steam through. Let it cool and dry. This is my preferred method because I find it very effective.
Spray blocking is the most gentle blocking process and is great for expensive and delicate fibers like silk and cashmere. This method should be used when you are not sure what kind of yarn you’re dealing with.
All you need to do is pin the pieces out to the desired dimensions. Using a spray bottle, spritz each piece until damp (but not soaking). Allow to dry and you’re done.
To sum it all up, it is best to understand what type of fiber you are using when blocking your knits. Wool and thick fiber knits will yield better results when it is wet blocked. With super chunky knits, I use a combination of methods. After wet blocking, if the result is not satisfactory, I will quickly steam block it as well. The same goes with spray blocking. Sometimes spray blocking is too gentle for certain delicate fibers so I will quickly run the steam from my iron over it. It is important to understand that these methods are recommendations and I urge you to always use your best judgement.