I just stumbled upon this web site, but i have been canning for quite a while. I have only done two or three batches of jam (grape jelly to be official). I am sure other more experience people will chime in.

I have seen white powder on the outside of jars from hard water. Especially if i use a pressure canner. I add a couple Tbspns of white vinegar in my pressure canning water to avoid this. Never used it for hot water bath (it will probably work though). I just wipe it off.

Your description i dont understand on the jam. What is white? The inside glass or the jam itself?

Sounds like hard water to me, but we will see what others think.

Hope this helps!
Chad