What is the name and where do you get the blue stain or paint for checking things like piston to head fit on a Z head and taper fitting, etc. NAPA and advance auto parts tried to sell me assembly grease and plastigage.
Thanks
Rick

Prussian Blue

As said above, Prussian Blue. Also ask for High Spot Indicator or Toolmakers Ink, it comes in either a brush bottle or spray can. Make sure it is not Toolmakers Bluing or Layout fluid, as that is not what you are loking for. Napa should certainly have it, more than likely the guy working there does not know what it is.

Grainer has it. Thanks, Dan.

In a pinch just use a wide tip permanent marker. John

Here you go:

http://www.mcmaster.com/#prussian-blue/=cxj3e7