Western blot
Most proteins are clear or cloudy in color, so scientists have to make them easier to see.  First, they block the proteins. That means they treat them so they will not bind to anything the scientist does not want.  They can use milk to do this.  Then they treat the proteins with a primary antibody.  The primary antibody sticks to the protein.  Then they treat them with a secondary antibody.  The secondary antibody sticks to the primary antibody.  The secondary antibody either glows or changes color.  This way, the scientists can see how much protein is there on the membrane and where it went when it moved through the gel.