Pat,
I have been experimenting with different paint chipping methods. I read a couple of articles but never remembered anything abut the salt having to be Kosher. It's possible that I missed it. Anyway, I have used Morton's table salt and the effect, although a lot of work, turned out really nice.
I have found that you have to be careful how much water you place on the model, you don't want too much. Also, use low pressure because higher pressure settings tend to blow the salt crystals off the model.
BTW, I have also "chipped" some paint using a small brush and aluminum paint. In my opinion, it is hard to tell the difference.
Hope this helps,
Chuck B.