100% Wool vs Man-Made Fiber
Our mill specifications require 100% wool. If there are ever any other fibers, which is very, very rare, the mills will notify us so we can communicate that variance to our customers.
One way to test your fabric’s wool content is to soak a small swatch in bleach. As we understand it, wool is acidic and immersing it in a chlorine solution, a strong base, initiates a specific neutralization reaction. Eventually the reaction neutralizes the wool with only the non-consumable structure remaining. However, some commercial processing aids intentionally alter the wool’s natural pH (i.e. to reduce shrinkage or aid in dyeing). pH changes intentionally made to wool may slightly impact the speed of the bleach test but, in our experience, do not alter the ultimate result. (We have not found references to the bleach test being used in the scientific, textile industry as a qualified test method. However, we have conducted tests on our own product and competitive products and found it to produce consistent results.)
We summarize our method below.
Cut a sample swatch (approximately 1-1/2" x 1-1/2") from a non-selvage section of fabric. Place wool swatch in a nonreactive, ceramic bowl and cover with approximately 6 oz. of chlorine bleach (e.g. Great Value Splash-Less Bleach, assumed to be 5.25 to 6% sodium hypochlorite solution). It is important to make sure your bleach is fresh. Bleach does lose its' potency faster than you may expect. Do not skimp on the amount of bleach used because using too little will not provide enough hypochlorite to complete the full neutralization reaction. Push swatch to the bottom of the bowl to assure saturation and full immersion. Observe swatch occasionally for several hours and push it back down to the bottom of the bowl to assure full contact with the liquid; not sitting on top of the foam layer generated by the reaction. Observe the bowl again after 24 hours (however it usually does not take this long, especially if your bleach is fresh).
You will observe a substantial foaming reaction over the first few hours as the wool fiber is neutralized. Depending on the weight, at hourly observations the swatches will begin to lose mass more rapidly than others. After several hours the foam will leave the surface, and there should be no distinguishable fibers in a few hours. If there are any distinguishable fibers, these fibers are not wool and represent the manmade content of the fabric. The manmade content will appear as a network of fiber, sometimes translucent, and can be plucked out of the liquid for inspection.
Two similar looking wools selected for testing. Pictured right, with the straight edges, is The Wool Studio's, "Tiny Black and Green Check".
Swatches in Bleach
Be sure to use fresh bleach and use enough to complete the reaction. Wool Studio swatch, right.
Wool fiber is being consumed by reaction. Wool Studio swatch, right.
Neutralization reaction nearing the end. Wool Studio swatch, right.
The 100% wool swatch has been completely consumed by the test. The test reveals the synthetic fibers remaining in the swatch, left.
The test reveals the synthetic fibers remaining in the swatch, left.