Part of a series that begins with Blocking Notes (Intro).
Blocking always involves water; the three major types of blocking differ in how much water you use and how it is applied to the knitted articles. Which method you choose mostly depends on the type of yarn, although the type of knit, whether you're blocking prior to seaming or after washing a completed garment, and the stitch patterns also have an effect. The ball-band from the yarn should have useful information on it, but the best method is to knit a number of swatches and try out different blocking techniques on them to see which is the best. This is particularly useful if the yarn is unfamiliar, or the finished garment should fit precisely (where stretching or shrinking will be an issue).
Wet blocking is the term generally applied to the process of soaking the knitted articles. Fill a basin with cool or lukewarm water, add a small amount of a detergent, and swish the detergent through the water. The cleansing agent can be a specialized wool wash, or a mild, slightly acidic hair shampoo. A gentle dish detergent such as Dawn also works well, as long as it's detergent and not soap (since soap is alkaline, it encourages fulling). Add the knitted article(s). You can swish the water through very gently to make sure the articles are thoroughly wet, which is why the water should be cool or at most lukewarm. After 15 or 20 minutes soaking time, pour off the water, pressing the excess water out of the articles, and rinse in cool water a couple of times until the water is clear. If the articles are heavy, I find pouring them into a strong colander makes pressing out the excess water gently much easier, without stressing the knitted fabric. Some people put the articles in a laundry bag or pillowcase (one that closes properly) and put them in the spin cycle in the washing machine; this is the sort of thing you want to test out on swatches first. Don't spin dry sensitive yarns such as cashmere that felt easily. If not spin drying, after pouring off the excess water, lay the article flat on a towel, and roll up the towel with the article inside, so that you end up with a rolled-up towel surrounding the knitted item. Leave for a few minutes and then unroll. If the article is still very wet, repeat with a dry towel, until the article feels damp but not wet.
Carry the article to the blocking area, supporting it completely to make sure it doesn't stretch (another use for the colander if the article is large and/or heavy). For blocking garment pieces prior to seaming, block each piece separately. Lay it out on the surface and press gently into shape with your hands. Pin down the edges if they're curling, or if you need to stretch the pieces into the right shape. This is where the schematic and tape measure come in handy; some people use specialized blocking boards with measurements printed on them, or checked gingham to make this part of the process quicker. If you're blocking an entire garment, then usually the pins aren't needed, you just press the garment into shape and leave it to dry (unless you're using a woolly board).
If you're blocking lace shawls or tablecloths, then you probably want to use a bed or the carpet (covered with a cloth) and really stretch out the article, pinning down each peak or picot edge. This opens up the yarn-overs to their full beauty. You can also use dressing wires. To make sure the shape is correct, you should measure the various axes to make sure they match, or draw concentric circles and/or lines on an old sheet and use that to block on. You can also use a specialized blocking board or lace blocking frame.
I like to use wet blocking with wool and yarn mixes that are predominantly wool, as the fibres often need soaking for the full effect. This also mimics the way I'll wash the item later, particularly garments. The yarn will usually soften and relax, and then “bloom” or fluff up a little, particularly if it's woolen-spun rather than worsted-spun. Wet blocking helps even out any inconsistencies in tension and is necessary to make colourwork such as fair isle even and flat. I also find lace blocks best with wet blocking as the work can be stretched better when it's properly wet.
Spray or spritz blocking is the method whereby you pin out the article first, and then spray it with clean water (distilled is best) until thoroughly wet, then leave it to dry. I find it not as effective as wet blocking, but for sensitive articles such as cashmere, or when not very much blocking is needed, it works.
Steam pressing is the method whereby you steam the article, using a hand-held steamer, the steam from a boiling kettle, or a steam iron. If using a steam iron, hold the iron above the pinned-out piece, or press through a pressing cloth (which should also be dampened). Make sure you press, lifting the iron off the article each time you wish to press another area, rather than moving the iron while still in contact. Let the steam dampen each piece thoroughly. Be careful with this method as the heat can damage the fibres, especially synthetic blends.