All About Pocket Knives

I know that stainless steel in the 300 grades is non-magnetic, but when
you are working with the 400 grades how do you tell them from regular steel?
A magnet will stick to both and except for the non corrosive properties
there is no visual difference.

From what I see most knives with stainless steel blades are in the 400 series as a magnet sticks to them like glue.

I usually apply a bit of Brichwood-Casey (brand name) gun bluing liquid with a Q-tip to a small spot. Even magnetic stainless won't take bluing whereas all non-stainless steels will. A couple of seconds of high speed buffing will remove the blue spot afterwards. Not saying that this is the only method. Just one I've found that works for me. Bluing will also affect the nickel-silver on liners and bolsters so be careful not to apply too much, but if you do, the buffing trick still works.