I thought I would copy a section of a post on the natural dyeing of textiles by Chris Buckley on the 'General' section of the forum as, within in it, was a very helpful warning of the dangers of washing textiles in detergent which have been dyed with morinda. I find it so much better to understand the 'why' of something rather than just be told not to do it! [The bolding of the text is mine.]
Silk and wool are both protein fibers. They take acidic vegetable dyes brilliantly and are a joy to work with, and the mildly acid dye bath doesn't damage them. You can get good reds, browns, yellows with just one dip. With cellulose fibers (cotton, hemp and so on) on the other hand, an acid dye will make hardly any impression on them unless you do a lot of mordanting, and even then you will probably need several dips. In the case of the morinda red favoured by Indonesian dye-ers you need about 10-20 dips for a good dark shade, and about 3-6 months work. With morinda, the mordant is an oily mixture which is pounded into the cotton so that some of it penetrates the fiber: the dye sticks to this oily mixture rather than to the cotton itself. Which is why washing morinda-dyed fibers in detergent is risky, since you will tend to strip out the mordant and the dye with it.
For the whole post see: viewtopic.php?f=1&t=2423&p=7284#p7284
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