Bluing

From Brooklyn Centre Wiki

Bluing came in a small deep blue glass bottle with a wide pop bottle type cap with a small hole in the middle which allowed for just a few drops at a time to be dispensed. I can't remember the brand name but it might have been Mrs. Stewarts.

Laundry wasn't the only thing bluing was good for, though.

I can remember my Dad making me a crystal garden out of a few small lumps of coal in a shallow dish or pan. On the first day, he sprinkled on a couple of tablespoons of table salt and a similar amount of water and bluing over the coal. The next day, he added a couple more tablespoons of salt. On the third day, he added at the bottom of the dish more salt, water, and bluing, plue some food coloring and/or mercurochrome.