Wool rug cleaning

A scaled fibre, seen close up

Wool is made of keratin, the fibrous protein also found in silk, fur and feathers. Its surface is not smooth: it is covered in scales, all facing the same way, like roof tiles. That structure is what gives wool its elasticity and its ability to spring back into shape — and it is also what makes it vulnerable.

Over the top of it lies a natural grease: lanolin, the wolvet of the Flemish workshops. Close to 97 % long-chain fatty esters. It repels water-based soiling — which is why a glass spilled on a healthy wool rug beads for a second before soaking in, and why you have time to act. An aggressive detergent dissolves it in a single bath. The rug comes out clean, but dull, dry under the fingers, and without its first line of defence.

Between pH 5 and 7, never beyond 8

Wool is washed between pH 5 and 7, that is, in a neutral to slightly acid medium. Beyond pH 8, alkalinity tips the fibre over: the scales lift, the fibre swells, yellows and can release its dyes.

The problem is that almost everything sold for cleaning is alkaline — washing powders, degreasers, household cleaners, carpet shampoos. On the ivory field of a Persian rug, that alkalinity leaves a yellow cast that nothing afterwards will put right; on a poorly fixed madder red, it opens the door to dye bleed. Hence two workshop rules: neutral soap, and rinsing until complete neutrality, not until the water looks clean. A soap that has been badly rinsed out goes on working in the fibre for months.

Below 30 °C: felting cannot be undone

Felting is the irreversible tangling of the scales under the combined effect of heat, moisture, alkalinity and agitation. Wool felts as soon as the temperature goes above 40 °C. That is why we wash below 30 °C, and preferably lower still.

A felted rug is recognised by touch before the eye: the pile becomes stiff and boardlike, the surface has shrunk and the rug no longer lies flat. There is no treatment that will reopen tangled scales. It is the only operation in this whole trade that is strictly beyond return.

Temperature protects the colour too. In cold water the migration of the dyes is very slow; it becomes markedly active above 40 °C. Cold water and wool go together for two distinct reasons that point the same way.

The sequence on a hand-knotted rug

Washing starts dry. Mechanical dusting by vibration and suction, on both faces: a living-room rug can give up as much as a kilo and a half of mineral dust, lodged at the base of the pile against the foundation. That dust is abrasive; wet, it turns into a mud that sets.

Then comes the colour-fastness test — a damp white cotton cloth, thirty to sixty seconds of gentle rubbing on a discreet area, then ten to thirty minutes under light pressure, up to an hour on an old piece. The colours are fixed if the cloth talks.

Then the bath: neutral soap, below 30 °C, brushed by hand in the direction of the pile. Never against it, which stands the fibres up and opens the scales. Repeated rinsing until the water runs clear, spinning by centrifuge — of the order of 1,200 revolutions per minute in the workshop — and flat drying in the shade, in a ventilated atmosphere, of the order of 22 °C and 45 % relative humidity, in under twenty-four hours, on a perfectly rigid surface. A wool rug dried hanging distorts under its own waterlogged weight.

What the wool gets back

A final brushing in the direction of the pile lays all the fibres back the same way: that is the gesture that restores the lustre, the way a rug has of changing tone according to the angle you look at it from. The colours then seem brighter. They are no brighter: the grey film that veiled them has simply been removed.

To keep it going between washes: vacuum regularly, including the back and the borders, move the rugs about from time to time, deal with organic stains quickly — they attract moth larvae, which digest precisely the keratin of the wool. And never put a dirty rug away: rolled up in an attic, a dirty rug is a larder.