Blocking is a method to set a knitted piece to its proper measurements, to relax and even out the stitches (especially helpful with Fair Isle), and to flatten curled edges. It involves wetting the piece by either immersing it until saturated, spraying it with water from a spray bottle, or steaming it with an iron. The improvement in the appearance of knitting can be dramatic.
The type of fiber you’re using determines whether you can use water and/or steam. Check the ball band for care instructions. Most fibers can be wetted, but some can’t; some can survive cold water, but not the heat of steam. For yarns that can’t be wetted, blocking is omitted.
You will need a cushioned surface into which you can stick rust-proof pins. Foam waterproof blocking mats are commercially available and easy to use. An alternative is a towel over carpet or a bed or, for small items, an ironing board; if your item is really wet, put plastic under the towel. It may take a couple of days for saturated wool to dry, though a fan will speed this up.
The most common blocking method is wet-blocking. To do this, immerse the piece in cool water, either plain or with a small amount of liquid soap or wool wash; wool wash has the advantage of not needing to be rinsed. Let it soak for at least thirty minutes, pushing it under the water occasionally if needed. If you use soap, rinse it gently with fresh water, swishing the piece, draining the water, and repeating until the soap is removed. Press gently on the wet mass (don’t wring or twist, or you will distort the stitches) to remove excess water, and carefully support its weight as you lift it. Roll it up in a clean towel and let it sit for a few minutes while the towel absorbs the water. Use a second towel if needed – you want the piece damp but not dripping. Put it onto your blocking surface, and if it doesn’t require careful shaping, you can simply pat it into shape. Otherwise, a good pattern will include a schematic giving detailed measurements, such as body length, shoulder width, etc., and you should pin the pieces to those measurements. Pins are especially necessary if you need to stretch the piece, in order to hold the stretched shape until dry. Use enough pins placed close together so that edges stay straight and don’t scallop. Start pinning in the middle of each side, then work your way to the corners. Ribbing should not be stretched and pinned; it is supposed to pull in. Let air dry. Wet blocking is a good process for wool, having the advantage of getting the piece really wet and allowing more relaxing of the stitches and more stretching of the piece when needed.
For delicate fibers like silk, cashmere, mohair, and angora, spray blocking is used, which involves pinning the piece to size and then spraying with cold water from a spray bottle. This dampens the fibers but does not saturate them. A variation is to lay a damp towel over the garment instead of spraying it. The piece (with or without the towel) is then allowed to air dry. This method can be used with any fiber that can be wetted, and it dries faster than the wet blocking method.
Steam blocking can be used for fibers that cannot be wetted directly, and works well for cotton, which can stretch out of shape if you’re not careful to support the heavy wet piece. Pin the piece to size, lay a cloth or towel, slightly dampened or not, over it, and slowly move the iron over the piece without directly touching it – let the iron hover an inch or two above the surface. The steam will reach the piece without the weight of the iron flattening the stitches or the heat from it scorching the work. Steaming is not recommended for synthetic fibers, which could melt from the heat. Over-steaming can flatten most stitches, even on heat-safe yarns, and can shrink wool.
If a garment is to be seamed, block it first in case you need to stretch the pieces to reach the desired size. Seams, once sewn, do not stretch much.
I am sure that, once you take the time to properly block your handknits, you will be pleased with the results.