A “sweat box” is used in rust bluing for two reasons:
1. To initiate and accelerate the rusting process
2. To create a consistent, reproducible humidity environment
Rust bluing can become agony for some who do not live in a high humidity environment, or if the season of the year is dry and cool. By employing a “sweat box” or rusting chamber, rust bluing can be carried out year round under identical conditions. I am a big fan of PVC pipe! It is remarkable what you can do with it. In my rust blue instructions, I outline how to build a steam pipe apparatus to steam the rusted steel and produce rust blue. It is constructed from a stainless steel pot w/lid, 3 in. toilet flange, pipe cap, and a length of cellular core PVC pipe (see below). That same steam pipe can be used as a rusting chamber by hanging the rusted steel parts in the pipe and placing it over the pot containing water; then covering it. You can also make several rusting chambers by cutting different lengths of PVC pipe and placing them in an aluminum pie pan containing an inch or so of water. Then placing the steel parts inside and covering.
Now that you have created a controlled rusting environment, you can develop a system for rust bluing based on known timelines. With all of my formulas, adequate rusting of treated parts can usually be achieved in two to three hours. This creates an even coat of fine red rust, similar to reddish brown “fuzz”. The rusted part is then steamed or boiled to convert the rust to black oxide. Once this pattern is achieved it is possible to blue a gun in only a day.
Many of my formulas require only two to three passes. Think of the time and money saved over other products on the market that can require up to a dozen passes. If you need more detailed photos of the steam pipe construction, drop me an e-mail.