I had some very pretty cotton lace, which was somewhat yellowish but which I wanted to be white. So I went to the drugstore and secured whitener:
I must admitt, I was not very sure about this, I feared the lace might dissolve or something, but to my surprise (and pleasure!), nothing happened, expect that the lace became whiter. It's not perfectly snow white now, but it doesn't even have to. Just a bit whiter was all I wanted, and my prayers were answered:
Before and after. The difference is not very significant in the pictures, but you have my word that the right one really is whiter than the left one.