What makes Navy Blue fabric go Purple?

[lljkk]

DS school uniform has navy blue sweatshirts. Many (but not most) of the children are sporting sweatshirts that have turned very purple-toned. They aren't necessarily the oldest/most worn sweatshirts, either.

What causes navy blue clothes to turn purple-ish? Is it some particular types of detergent? Want to know what to avoid!

washing right side out?
drying in sun right side out?
(always wash and dry dark stuff inside out)
I suppose it could be a detergent thing - you could use a 'colour' one...

But at the moment I don't have anything that's faded to the purple tone I mean. And we have at least sometimes done those things, too. Maybe it was just a bad batch dye on some of the school sweatshirts?... but I think I've come across purple-tone Navy blue stuff in charity shops sometimes, too.

in that case I reckon poor dye lots / cheap sweatshirts...

my guess is its the washing powder / liquid that you use...

colour products do not contain 'optical brightners' aka bleach. so will not bleach clothes

(if you spill bleach on dark blue it odes go a purple colour)

Most non-colour products contain optical brightners aka bleach. However some non bio liquids (such as fairy / persil non bio liq / ecover) do not contain optical brightners so these wont bleach your colours.

Asfar as im aware pretty much all bio powders have optical brightners in (but maybe not ecover, as they have a whitening powder sold seperatly for whites)

Would probably be a good idea to wash the dark jumpers in either a bio coloured product or a non bio liquid (if you need non bio)to protect the colours in future

You need to use a detergent for coloureds i use Ariel colour for my coloured garments and Ariel (in the green box) for my whites. As nanny said you cant use a bleach containing detergent on colours or it will fade them, hence your jumpers going purple.
If you check out Which website and www.ukwhitegoods.co.uk they both say that Ariel is by far the best washing powder to use.

Ah, I was wondering about bio powders, we have started using them only very recently and I was afraid that they might be a cause, but wanted someone else to explain why since it was just a hunch! Many thanks.