Identify silk
In a rug, silk is a status symbol and a frequent target for forgery. Mulberry silk costs ten to twenty times as much as viscose or synthetic bamboo silk. This page shows how to tell genuine silk from imitation.
#What silk means in a rug
Genuine silk comes almost exclusively from mulberry silk, the cocoon of the Bombyx mori silkworm. The filament of a single cocoon is 600 to 900 meters long, gossamer-thin, smooth, and reflects light in a narrow angle. These properties make mulberry silk so valuable and so hard to imitate.
In the rug trade, three materials are sold as silk, but only one is actually silk.
Mulberry silk from Bombyx mori, often from Bursa in Turkey or from Iran. The genuine article.
Viscose, a cellulose-based synthetic fiber made from wood or bamboo. Often marketed as bamboo silk or banana silk. It has a strong sheen but is less resistant to light and abrasion.
Mercerized cotton, treated with caustic soda to enhance its sheen. Rarely sold directly as silk, but occasionally used in cheaper imitations.
#Test 1: Burn test
The most reliable test, though destructive. Pluck a tiny fiber from the pile in a hidden spot (back of the border or pile root). Hold the fiber to a match flame.
Mulberry silk behaves like wool: it swells into small black beads, smolders to powder, and smells of burnt hair. The ash crumbles between your fingers.
Viscose behaves like cotton: it burns quickly with a clear flame, smells of burnt paper, and leaves a whitish ash.
Synthetics (polyester, polyamide) melt rather than burn, drip, smell of plastic, and leave a hard bead.
This test is not reversible, but a tiny fiber from a hidden spot is no problem.
#Test 2: Sheen at an angle
Mulberry silk changes its sheen dramatically with the viewing angle. Turn the rug or move around it. A genuine silk surface that looks matte from one angle will glow bright and powerful from another.
Viscose also has a sheen, but it is less directional. A viscose surface gleams evenly strong from most angles, without the characteristic shift.
Mercerized cotton has a softer, calmer sheen, almost matte, and barely responds to changes in angle.
This test works best in daylight and with the rug fully unrolled. On folded or stacked pieces it is less reliable.
#Test 3: Hand feel and warmth
Grip a spot on the rug firmly with your palm and hold for a moment. Mulberry silk absorbs body heat quickly and releases it just as quickly. The spot feels warm, but cools within seconds.
Viscose and synthetics conduct heat less well. The spot stays warm longer, sometimes with a slightly sticky aftertouch.
The hand feel itself gives another clue. Mulberry silk feels smooth and cool, almost like polished stone. Viscose is smooth, but a touch softer and more sluggish. Mercerized cotton is smooth, but noticeably coarser than mulberry silk.
Knot density is an additional indicator. Mulberry silk allows 1 to 2 million knots per square meter (typical Hereke). Viscose rugs rarely exceed 400,000 to 700,000 knots, because the fiber cannot be spun as thin.