Identifying fibres: feel, crease, water and burn tests

1Why this matters

At a second-hand clothes stall or when buying cloth by the metre at the market, there is often no label. Is this "silk" scarf really silk, or polyester? Will this cloth take a hot iron? Simple tests with your hands, a drop of water and, under supervision, a small flame can answer these questions.

This lesson gives you four tests, in the order you should use them: the harmless ones first and the burn test last.

2Test 1: look and feel

Handle the fabric and look at it closely in good light.

The feel test is quick but unreliable on its own: modern finishes can make polyester feel like silk or cotton.

3Test 2: crease test

1. Crush a corner of the fabric tightly in your hand for about 30 seconds.
2. Open your hand and watch.

Cotton, linen and rayon stay creased. Wool, silk, polyester and nylon spring back, mostly smooth.

4Test 3: water drop (absorbency) test

1. Lay the fabric flat and place one drop of water on it.
2. Watch for 30 seconds.

On cotton, linen and rayon the drop soaks in almost at once. On polyester and nylon it sits on top as a bead for a long time. On wool it beads at first and then soaks in slowly, because the surface of the fibres repels water although the inside absorbs it.

5Test 4: burn test (only with your teacher)

The burn test gives the clearest answer, because each fibre group burns in its own way.

Safety rules for the burn test

• Only with your teacher present, in a well-aired room, and never on clothing someone is wearing.
• Tie back long hair, roll up loose sleeves and remove scarves.
• Work over a metal tray or a ceramic tile, with a bowl of water next to you.
• Test only a few threads or a piece about 2 cm square, taken from a hidden seam allowance or a spare scrap.
• Hold the sample in long tweezers or tongs, never in your fingers. Melting synthetics drip and stick to the skin.
• Bring the sample slowly to the edge of the flame of a candle or match; do not push it into the middle.
• Drop the burning sample into the water. Do not breathe in the smoke; waft the smell towards your nose with your hand.

A blend gives mixed results: polyester-cotton burns fairly quickly and leaves some soft ash together with small hard beads.

Worked example: three unknown fabrics

Fabric P springs back after crushing, a water drop sits on top as a bead, and the burn test shows melting, dripping, black smoke and a hard bead. Every result points the same way: a synthetic, and the black smoke and sweetish smell suggest polyester.

Fabric Q stays creased, absorbs a water drop at once, and burns quickly, smelling of paper, leaving soft grey ash. It is a cellulose fibre: cotton, linen or rayon. It is matt and soft with no slubs and does not hang heavily, so cotton is most likely.

Fabric R feels smooth and shiny like polyester, but it springs back from creasing, burns slowly, smells of burning hair and leaves a black bead that crushes to powder. The burn test shows protein, not synthetic: it is silk. This is why you never rely on the feel test alone.

Practice

Solution. A cellulose fibre: cotton, linen or rayon. Wool, silk, polyester and nylon spring back.

Solution. Protein (animal) fibres: wool and silk.

Solution. The sample may flare up suddenly, and synthetic fibres melt and drip. Melted fibre is very hot and sticks to the skin, causing a deep burn. Tweezers keep the fingers away from the flame and the drips.

Solution. The claim is false. Silk is absorbent and burns to a crushable bead with a smell of hair. A water drop that stays on top and a hard, melted bead both show a synthetic fibre, most likely polyester.