Re: Hennotannic acid is a dye rather than a pigment
Posted by atul on March 09, 2000 at 10:45:05:
In Reply to: Hennotannic acid is a dye rather than a pigment posted by Catherine Cartwright Jones on March 02, 2000 at 20:26:54:
: Hennotannic acid is a dye rather than a pigment .... (pigment is an
: insoluble colored material that you suspend in medium like varnish
to
: make ink)
: The most certain way to get henna to stain is to add something very
: sour to powdered henna leaves. Henna releases dye in an acidic
: environment. Mixing lemon or lime juice into henna powder and
: leaving it a few hours is a very efficient way to get dye release.
In
: a standard 50x microscope field, lemon juice is 5 - 8 times more
: effective than water at making dye release (so its available to
bind
: with collagen). There is a color release process ..... the dye
stains
: the skin most strongly in the 12 to 48 hours after adding acid ...
: then diminishes over several more days until old henna paste barely
: stains skin a sad tangerine color.
: Hennotannic acid seems very reactive with oxygen .... so if you
try
: to just take hennotannic acid from the leaves (that brownish liquid
: that appears at the surface of henna left out too long) it's not
very
: useful. Its reactivity diminishes on contact with air ... or
that's
: what I think I'm seeing, with the color sequence over several days.
:
: If you want to see a gif of the dye molecule of henna .... email
me.
: Maybe you can make better sense of why exposure to air spoils the
: dyeing power of henna than I can.