Blocking: what it does and when it matters

Wetting a wool fabric lets the fibres move relative to each other; drying it in a held shape lets them set there. The stitches even out, the fabric relaxes to its natural dimensions, and anything stretched into shape while wet largely stays that way. For lace this is not a finishing touch — an unblocked lace piece is a crumpled mass and a blocked one is the thing in the photograph.

Synthetic fibres do not do this, because there is nothing in them that responds to water in that way. Acrylic can be shaped with steam, which softens it permanently and is often called killing it, and the result is flatter and drapier and cannot be undone. That is a legitimate finish and a very different operation from blocking wool.

Lace

EssentialThe pattern does not exist visually until it is opened out.

Anything to be seamed

Strongly worth itFlat, even-edged pieces are far easier to sew together accurately.

Anything that has to fit

Worth itBlocking is where a piece reaches its real measurements, and measuring before it is the reason a garment surprises somebody.

Garter stitch worn objects

OptionalIt evens the fabric a little. A scarf will be fine either way.

A dishcloth

NoIt is going in the sink.

1. 1

   Step 1: Soak in cool water

   Fifteen or twenty minutes, with a little wool wash if you have it. Cool and still — warm water and agitation together are what felt wool, and that is not reversible.

2. 2

   Step 2: Get the water out without wringing

   Press it out against the side of the bowl, then roll the piece in a towel and press. Wringing distorts the fabric and can felt it.

3. 3

   Step 3: Pin it out to the measurements you want

   On a towel, a foam mat or a bed. Measure rather than eyeballing, and pin generously — every unpinned edge between two pins will scallop.

4. 4

   Step 4: Leave it until completely dry

   A day, sometimes two. Moving it while it is still damp undoes most of the effect, which is the commonest way blocking appears not to have worked.