Why Silk Deteriorates, and What Museums Have Learned About Slowing It

In 1914 the Smithsonian put 15 silk gowns attributed to First Ladies on display. Eleven of them stayed out for the next 73 years.

The first home for those gowns had large west-facing windows, with heavy curtains drawn only some of the time. In 1931 the exhibit moved so that north light could stand in for lamps, and daylight wasn't shut out until the 1950s. By the time a 1995 study of the collection's silk was published, light in those galleries was held to 3 footcandles or less, and some gowns had become too fragile to show. Sarah Yorke Jackson's wedding dress had crumbled at the hem, so only its embroidered chiffon skirt stayed on view.

Your pillowcase will never stand in a museum for 73 years. The chemistry working on it is the same, though, and those gowns show what harms silk better than any care label can.

Why does silk deteriorate?

Silk deteriorates because it's a protein, and light, heat, moisture and chemicals can all break its long protein chains. The fiber itself is fibroin, spun by a caterpillar and held in the cocoon by a gum called sericin. As the chains shorten, the cloth loses strength. It may yellow, then stiffen, then split along its folds.

Why is sunlight so hard on silk?

Light cuts silk's protein chains, and the damage builds up with every hour of exposure. The Canadian Conservation Institute describes light damage as cumulative and irreversible, and counts it as brightness multiplied by time, so halving either one halves the damage. Direct sunlight can run from about 3,000 to more than 9,000 footcandles, roughly a thousand times what those gowns get, or more. Ohio State University Extension adds the part you can see: sun fades silk and can turn white silk yellow.

The Smithsonian-linked study found a twist. Sericin, the gum normally washed away during processing, yellows easily but also shields the fiber from light. The authors warned that 20th-century silks, processed until the gum was gone, are "at extreme risk for light damage." So a new scarf left on a sunny chair may be less protected than you'd assume.

Light doesn't explain everything. In a preliminary 2009 study, researchers from the University of Southampton and English Heritage found that light with the UV filtered out did little damage to new silk, while heat combined with high humidity did far more.

What does sweat do to silk?

Sweat can weaken silk, and a pillowcase or camisole meets plenty of it. Ohio State Extension blames chloride salts in perspiration and deodorants, which can split silk at the underarms and damage some dyes. The same fact sheet warns against alcohol-based hair spray and perfume, and against strong alkaline detergents. Conservators see the long-term version: on one House of Worth ball gown, a conservator found the underarm silk shattered, most likely by acid from perspiration.

The fix costs nothing but a sink. Silk put away with sweat and oils still in it can yellow and draw moths, which is why storing silk clean matters more than any sachet.

Does humidity damage silk?

Yes. Damp air invites mold, and heat speeds up the chemical damage. The Canadian Conservation Institute names damp, above 70% relative humidity, as the one humidity condition textile collections should always avoid. Mold can take months to appear at 70% and only days at 90%. Its rule of thumb for heat is blunt: every rise of 9°F (5°C) doubles the rate of decay and halves the life. That makes a hot attic in August, or a damp basement, a poor place for a box of silk. Very dry air has its own cost, making old fibers more brittle, so a normal living space suits silk better than either extreme. If damp has already won, see how to remove mold from silk.

What is shattered silk?

Shattered silk is old silk that has split into strips and shards, usually because it was weighted with metal salts. Silk was sold by weight, and degumming takes off roughly a quarter of it. So in the late 19th and early 20th centuries, makers put the weight back, and often added more, by steeping the fiber in metal salts, most commonly tin. The fabric came out heavier, with a better drape. Decades later it split along its folds.

The First Ladies study gives an example: the tin-weighted silk lining of Edith Roosevelt's 1905 gown, which the authors describe as brittle and shattered. Old quilts show it too. A conservator at the Denver Art Museum found the printed silk ribbons in an American quilt from 1914 severely shattered, which the museum calls a common problem with historic silks. In 1938 the FTC ruled that silk weighted above 10% (15% for black) had to be labeled as weighted.

Most weighted silk you'll meet is vintage. By the early 2000s few silk items were weighted, but the practice lasted longer than you might guess: the Smithsonian study included a tin-weighted satin from Patricia Nixon's 1969 gown.

What do museum conservators do about it?

They cut the light, control the air and handle the silk as little as possible, because no treatment reverses the damage. Belgium's MoMu fashion museum, a partner in university research on weighted silk, says plainly that the aim is to slow the decline, since stopping it isn't possible. In practice that means:

• Low light, with fragile pieces rotated off display so they get long rests in the dark.
• Closed cabinets or drawers, which keep out all light.
• Great care with water. The First Ladies authors warned that any wet treatment can strip what's left of the sericin from an old fabric and remove degraded fiber along with it.
• Sheer support. Fragile areas are usually stitched under an overlay of silk crepeline or nylon net, and some treatments use adhesive support as well.

What does this mean for the silk you own?

It means the museum rules work at home in simpler form, because your silk gets washed and used in a way a First Lady's gown never will.

Threat	What museums do	What you can do
Light	3 footcandles or less, no daylight	Dry silk in the shade. Keep scarves in a drawer, and don't leave silk on a chair in the sun.
Sweat and oils	Clean rarely, and test first	Hand wash cold, or machine wash on a gentle cycle in a mesh bag with mild detergent. Wash before storing.
Heat	Cool, steady storage	Hang or lay flat to dry. Do not tumble dry. Skip the attic.
Damp	Keep humidity below damp levels	Dry completely before putting away, and use a cotton bag, not sealed plastic.
Chemicals	Test everything	Do not bleach. Let perfume and hair spray dry before silk goes on.

Everyday silk also wears from plain use, and how long a silk pillowcase lasts covers what to expect. If it's already turning, yellowing can often be eased with a gentle wash.

A vintage piece that's already splitting is another matter. Don't wash it. Keep it flat, dark and cool, cushioned with acid-free tissue, and if it matters to you, ask a textile conservator. The American Institute for Conservation runs a searchable directory.

Looking for silk you can wash at home? See LS Silk pillowcases →

The people minding those gowns got there one step at a time: a north-facing room, then no daylight, then 3 footcandles. You can skip straight to the end of that story for free, by keeping your silk out of the sun.

Frequently asked questions

Does sunlight through a window damage silk?

Yes, glass doesn't solve it. Researchers studying the First Ladies gowns aged silk with sunlight through glass and found its proteins became easier to dissolve, a sign of breakdown. Light damage adds up over time, so a bright windowsill is a poor home for silk.

Does silk rot?

It can. Mold can stain and weaken silk in damp conditions, although cotton and linen are more vulnerable. Over long periods, light and heat also shorten silk's protein chains until it turns brittle, which can look like rot with no mold involved.

Why is my silk turning yellow?

Sunlight, and sweat and body oils that weren't fully washed out, are the usual causes. Ohio State University Extension notes that sunlight can turn white silk yellow. A gentle cold wash often helps with buildup, but yellowing from light is harder to undo.

Can shattered silk be repaired?

It can be supported, but the damage can't be reversed. A textile conservator can stitch a fragile area under a sheer overlay so a piece can be handled or shown. Washing or mending it at home usually makes things worse.

What humidity is best for storing silk?

Keep it below 60% relative humidity with some air moving, and avoid anything above 70%, where mold becomes a real risk. The EPA suggests 30% to 50% for homes in general. A small hygrometer will tell you what your closet is doing.

Is silk still weighted with metal today?

Rarely, though the practice hasn't completely disappeared. Most weighted silk people encounter is vintage, from the late 1800s into the 20th century. If you're buying new silk and want to be sure, ask the seller.

Related reading: What Is Silk and Where Does It Come From? · How to Care for Silk Clothing · Silk Pillowcase Guide