I used a pair of dingy socks (that of course used to be quite nice like a hundred years ago) and gave this BB a go with them. I only soaked one in a water/peroxide mixture. I let it sit there for about 20 minutes, then I rinsed, wrung it out and hung it to dry in the sun for the day.
The difference is slight, but it is there.
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Before
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During
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Hung out to dry
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After. Like I said, it’s only a small change but it is whiter than before.