[Kate de Courcy]

Kate de Courcy asked the Naked Scientists:
Dear Chris

I bought a light blue denim sun hat last year.  It has a decorative white (cotton I think) band round it with scarlet spots on.  I would like to wash the hat but fear the red dye may run and turn the whole hat pink. The hat was a very good find and I do not wish to spoil it.

Someone I spoke to told me that soaking in vinegar prevents colours running, and, while I do not wish the hat to smell of vinegar, wonder if that procedure/tip is known?  If vinegar works, would malt vinegar do?

Washing the hat in very luke warm soapy water might prevent the red dye from running, but I would be most grateful if your team / programme could help with the above query.

With many thanks.

Kate de Courcy
What do you think?

[chris]

It sounds to me like the acidic nature of the vinegar might be able to affect the chemistry of the dye so that it binds more strongly to the base fabric i.e. is less easily leached. How, exactly, this happens though, I'm not sure.

Perhaps someone with some expertise in dyes can advise me?

Chris