Indigo-the-dye-molecule is the main coloring matter extracted from
indigo-the-plant and from woad-the-plant.
Blue jeans fade, not due to any problems with indigo, but because their blue
threads are dipped very quickly into the dye bath & out again, so their
coloring is all on the outside.
Like an indigo 'O' in cross-section.
If a dowel is painted, and its outsides sanded down, it is no fault of the
paint that the dowel color shows.
Ann in CT
--- On Tue, 2/1/11, annbw...@aol.com <annbw...@aol.com> wrote:
> The dyestuff in woad is chemically
> very similar (in fact, it might be
> identical, but I can't verify that off-hand) to that in
> indigo, but woad
> doesn't contain as much, and, naturally enough, European
> woad dyers resisted the
> "new fangled" indigo. Both woad and indigo are vat
> dyes--the blue dyestuff
> is not water soluble, a real drawback in dyeing, and has to
> be treated with
> a strong reducing agent to make it water
> soluble. The baths smell bad
> partly because guess what the strong base was back in
> the day--stale urine.
> Although I understand stale urine doesn't smell like the
> fresh stuff. The
> fiber/fabric is dipped in the bath, and, as it comes out
> and hits the air,
> the dyestuff is re-oxidized and turns blue.
>
> Blue jeans run mainly because there is excess dye left on
> the surface of
> the fabric that is not absorbed into the yarns/fibers.
>
> Ann Wass
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