Another useful plant from Buchanan's A Weaver's Garden
Page 124, 126: Kelp is a source of sodium carbonate and sodium hydroxide (lye) and can be used to make hard soap.
Kelp is a very common seaweed around Vancouver Island. I know how to top and tail a piece of fresh kelp and play it like a horn. For those of you who didn't play with kelp as a kid, it is shaped like a very long, flexible hollow tube. It is many feet long and tapers from a bulb about five inches in diameter to a pencil thick end. If you cut the bulb off one end, it looks like the bell of a trumpet and if you cut across the skinny end where it is still about an inch thick, you get something a little like a trumpet mouthpiece only slimy and salty.
Now I have a second use for kelp if I want.