Kev, I normally crumple up some tin foil, put some mustard on it and fold it over the blade.
Most people will tell you to leave it in the foil, but you should take it out if you want any kind of striping effect. Let it set with the mustard on the blade (should have clumpy stripes or spots) until it's almost dry. (half hour tops) wash it off and see what you have. If you're using 10XX steel it should have a case hardening color to it.