Indigo is among the oldest and most treasured dyes throughout history. As it is with such precious things, there are some peculiarities about indigo dyeing, which are unfortunately little known in Germany. Abroad, this information is more widely known and treasured.
Indigo can rub off when exposed to heavy mechanical stress. This so-called “crocking” is not only normal, but is supposed to happen; it demonstrates that it is indeed true indigo and not some other blue colour.
The characteristic indigo blue is actually an oxidization of the indigo pigments as they interact with oxygen in the air after the yarn comes out of the dye bath:
Indigo pigments get attached to the fibre in the dye bath, and once the fibre comes out of the bath the yellow-greenish colour transforms into the typical indigo blue!
It is tricky to catch these precious seconds in a photo, but check this one out. The yarn is coming right out of the dye bath, and while the lower part of the skein is still greenish, the top is already turning blue!
Unlike the usual plant dyes, indigo does not form a chemical bond with the fibre, but rather a physical one: it attaches itself to the surface of the fibre. This leads to the so-called “crocking” effect when the fibre is subjected to mechanical stress. Some people will recall this from times when jeans were still dyed with real indigo; when wearing them for the first time, the blue would rub off on hands and thighs. A sure sign they were real jeans and not just some blue trousers!
Wearing jeans puts more stress and wear on the fibre than yarn is exposed to, but indigo-dyed yarn will still show crocking while it is being knit, especially on fingers and bamboo needles. The blue rub-off will wash off your hand easily. The finished knitted object, though, will not crock.
We have tested this for you with our own yarn. Socks knitted from our indigo-dyed yarn make it easily through a whole heavy-duty workday in safety boots with no crocking! No rubbing off, just as expected.
This way for general advice on how to handle natural dyed yarns.