Whats an evap line?

Question

Can anybody tell me what an evap line is? 
And how to know a bfp from an evap?

Answer

An Evap can have color and it usually does. An indent line doesn't have color. An Evap has uneven color. The line isn't just faded, but not solid in color.

Answer

Oops yes Stacy is right. I was thinking indent. Sorry!

Answer

Evap is a line on a test after it dries without any color. A positive test will have dye color on the 2nd line, an evap will just be colorless.