A cold blue does not work as well as a hot blueing tank, but nonetheless a nice finish can be achieved that will last many years! The best blueing that I have ever used is Super 44. It can be purchaced from brownells.
Keep in mind that the blueing job will only be as good as the prep work. For cleaning I like to use vineagar and ammonia mixed with a little liquid dish soap.
after cleaning, be sure to polish the metal surfaces and wash and rinse again. Lastly use a little Brake Clean and warm the metal to about 90 degrees or so. Then apply the blueing. After rubbing the blueing in to get an even color, wash & rinse thouroughly. Reapply untill desired color is achieved being shure to wash with ammonia and rinse between coats.
Note: The blueing will absorb oil so be sure to coat heavily and keep coated untill it no longer "dries out". This will take many coats of oil. Once it is "set", it will last many years.