Denim - The Details
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Indigo works by a chemical reaction called oxidation-reduction.
Indigo does not dissolve in water. It must be
reduced — i.e. the oxygen must be removed— in the
presence of alkali
by a reducing
agent such as
thiourea dioxide
(thiox), sodium
hydrosulfite, Zinc, or bacteria. Upon reduction, indigo
becomes colorless and water soluble. In this state,
indigo has a high affinity for cellulosic fibers and enters
the open spaces of the fiber. The dyed fibers are then
exposed to air, which oxidizes the dye molecule back to
its insoluble form. The insoluble dye particles are
trapped inside the fiber, coloring them permanently blue.
Unlike most dyes, indigo forms a mechanical, not
chemical, bond.Ok. So in it's reduced state (oxygen taken out, water soluble) indigo is colorless and will adhere to fibres. When air is introduced (oxidization no longer soluble) the fibres are turned blue. This is why in rope dyeing they are put in the vat, taken out, left to dry and then the steps are repeated to achieve the desired hue/darkness.
hope this helps!
heres the link i pulled that blurb from. I'm no scientist! (opens as PDF)
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&ved=0CDEQFjAA&url=http%3A%2F%2Fblogs.cornell.edu%2Fgarden%2Ffiles%2F2009%2F04%2Fintroduction3.pdf&ei=dWWsUO_aPMuy0AH3jIDwBg&usg=AFQjCNE1XEx_k9aie3imZ-4SAVLwDn1poQ -
That makes sense, thanks. It's been a long time since organic chemistry at university, so I'm pretty rusty on some of the theory.
Extrapolating from this it would seem logical that the greater the 'rest' time between dips, the more intense the colour.
So for maximum indigo colouring, you would go for a lot of dips, with a long rest time between dips.
Yeah?
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14.5 oz LHT sample, 21oz standard, SBG, 18oz, 23oz
