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I don't know the book title, but here is information on bluing laundry rinse: https://sciencing.com/bluing-liquid-6142623.html
The liquid variety was around in the 1900s, and was used to make white fabrics look brighter. It contains a small amount of blue dye, which is toxic and permanently stains fabric if applied directly to it. Liquid bluing is still available today.
Ramona and her Mother from the Ramona Quimby?
- For some reason, Mrs. Rudge’s words, there’s no such word as can’t, ran through Ramona’s mind. Of course they could get that bottle of bluing.

So, it's a novel where there are these two children— a boy and a girl, and either the boy is visiting the girl's house, or the other way round.
They make a pretend ocean with a bucket or a sink or something, but believe it doesn't look right due to not being blue.
Then, one of them (I think it's the girl) sees a bottle of liquid called "bluing", which... IDK what that is, but it seems like blue dye, and they both agree to use it to make the water blue.
The boy is a bit dubious that they'd be able to reach it, but the girl remembers that her teacher said, "There's no such word as 'can't'" (Not sure if she was trying to be inspirational or because it's a contraction... Even though 'there's' is also a contraction!) and decided that meant they definitely could.
They can reach it, but unfortunately, it spills on both of them, and they have to strip down to their underwear and have their clothes washed. The narration says that the girl wouldn't have been embarrassed if it happened when she was a preschooler, but right now she was embarrassed because "underwear was private". It didn't elaborate on how the boy felt.
Edited by Unicorndance