indigo question

[Betty & David Eyer <Betty_and_David@compuserve.com>]

Poster: Betty & David Eyer <Betty_and_David@compuserve.com>

Manus MacDhai wrote: 
>>During one tour, when the guide
was talking about the production of indigo, she stated that 
processing of indigo from plant to dye was toxic even carciogenic.<<  

Sorry to take so long to answer, but I have been on vacation....

There seems to be some sort of campaign in the modern world to discredit
'natural' 
dyes as being toxic.  Many of them are - but their modern equivalents are
also toxic, so I don't get the point.  If you are dealing with chemicals
(which is what dyes are all about), then you need to educate yourself and
take proper precaution.  Government regulation on handling and disposing of
hazardous materials can be very frightening; when you need some sort of
perspective, look up the regulations on disposing of table salt.  

Anyway, back to indigo.  The plant was processed by composting the weed
into a paste, then the paste was dried and  ground into a powder or by
pressing it into cakes or balls for sales and storage.  Surely, if you had
to handle it while it was composting or grind it or whatever, and you got
lots of it in your lungs, it would not be good for you.  But I do not know
of anything specifically harmfull about the plant itself.  

Once you are ready to use the dye, you have to do some sort of 'vat'
process.  Indigo, woad and  japanese 'buckwheat' all have the indigotin
chemical, which is not water soluable.  You have to put it through a
chemical process to deprive it of the oxygen molecules so that it will bind
to the fibers.  When the dyed fibers are returned to the air and and the
indigotin rebinds with oxygen, then the fibers turn blue.  The chemical
process IS toxic.  The oldest method involves fermenting the indigo paste
in wheat bran and old urine which produces uria and ammonia.   More recent
methods include saxon blue, and the japanese zinc vat, all using strong
toxic chemicals.  Without proper ventilation, rubber gloves, etc. I can see
that it would be a health problem, but it is certainly not worse than
cotton mills or tobacco processing, or tanning leather.

Magdalena
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