Yes. Natural amber in most cases floats in salty water and sinks in fresh water. This is how in some places, for example the Baltic Coast, you can find it washed up on the shore after stormy weather.
It would work, I wouldn't recommend anything scented though, as it may cause problems. Also, quick warning to be careful while drying, I'd say put the dryer on low or...
This statement refers to many cities that put additives in the water supply or well water that is high in iron. You can still use tap water, if you choose.
Three tests can be helpful here: scratch test, saltwater test and heating/smell test. Scratch test: Take a needle and scratch the stone in an unobtrusive spot; plastic will leave elastic...