I came across this PetaPixel article on using Plumber’s Tape as a Cheap Way to White Balance Photos. Sounded like a good idea so I gave it a try.
Here are my findings, you mileage may vary.
Three pictures all taken with the Canon 7D on a tripod with shutter release, same exposure & lighting. The comparison would be the 7D’s auto white balance, the plumbers tape white balance corrected in Lightroom and using an expo disc to set the custom white balance in the 7D before taking the shot.
Plumber’s tape, too warm. expo disc too cold, 7D auto WB, just right. For my money, the 7D auto white balance nailed it.