how to measure flatness of coated metal

[APH]

What is the cheapest and fastest way to find out if my coated surface is flat. The plate is coated all around, so I can't use one side for reference.

Thanks
APH

 

[IRstuff]

The surface of the coating or of the substrate?

TTFN

 

[ilan7]

Just measure the coat thikness using a coat gage (Transcat.com or davis instruments)

 

[tomwalz]

How flat?

Not too flat - Put a thin coat of liquid on it like water on a flat roof.

Pretty flat (0.001") - like a saw blade - use a straight edge and a light source behind it

Really flat - reflected laser light