I learned how to do rust bluing from Dr. Gaddy's posts. Very informative.
You can look it up through this site.

My etching solution is made from 4" diameter PVC with a solvent welded bottom cap and a solvent welded coupler fitting that has threads for a cap to screw on.
I used 15% by volume etching solution and 85% distilled water in a 36" PVC that has a line mark for 34 so it covers 32" barrels.

David