Building a “Rust” Cabinet

There are a variety of processes, collectively known as "bluing" which are used to achieve a blue or black finish on gun steel. Bluing is actually a type of controlled oxidation, a form of rust, that yields some protection to the metal. A common process requires the immersion of gun parts in a hot caustic bath, followed by rinsing and oiling after the desired color and intensity are achieved. This process is relatively quick and can be automated, which is why most large-scale manufacturers use it.

Alternative methods require a much smaller investment but more time and hand labor. One involves exposing the polished, cleaned, and degreased metal to acid fumes while another requires painting a corrosive liquid on the metal and allowing it to act for a period of time. The parts are then removed and wire-brushed to remove the brown fuzz that develops, exposing the metal for more applications of the corrosive fumes or liquid.

This cycle is repeated until the desired color and intensity is developed, at which point the parts are rinsed. Rinsing in water turns the brown to blue or black and "sets" the finish, that is, it tends to resist further rusting. An application of oil completes the process. Use of the fume method requires a sealed container to enclose the steel parts and the acid solution. The painting method also requires a closed container in order to maintain a humid atmosphere to enhance rusting.

The cabinet I built is intended to be suitable for either method. Basic construction is from 1/2inch plywood, treated on the inside The "Rust" Cabinet: While I used a piano hinge on the door, any similar hinge will suffice. Polyurethane caulk sealed the joints, duct tape covered all the exposed edges and the wood was finished with spar varnish. The incandescent light bulb, controlled by the rotary dimmer outside, heats the interior of the cabinet allowing a humid atmosphere while eliminating condensation problems.

with multiple coats of spar varnish. I bought steel angle iron pierced with a multitude of holes to reinforce the outside corners. Holes were drilled through the plywood using the holes in the angle iron as guides. I used stainless screws to go through the plywood from the inside and salvaged carbon-steel nuts on the outsides of the angle iron. Once constructed, polyurethane caulk was used to seal the joints and duct tape covered all the exposed edges of the plywood.

This sealant helps slow the absorption of moisture and forestalls delamination. The skids are from a surplus length of pressure-treated deck handrail. The door swings on a piano hinge I salvaged from — of all things — an old piano. The spring latches were given to me by a retired machinist. Mine was originally intended for greenhouses. This contains either acid for a fume bluing process, or water for the "painting" process. This heater lacks a temperature control but one could be retrofitted later.

There is an incandescent bulb in a ceramic fixture mounted inside and controlled by a rotary dimmer mounted outside. The light bulb is intended to help heat the interior of the cabinet and allows a humid atmosphere without allowing condensation. I mounted a cheap digital thermometer/hygrometer, originally intended for use in a greenhouse, inside so I can monitor temperature and humidity. It’s all about process control, right? Inside, down at the bottom, is a potpourri heater.

Essentially, this is a heavy crockery bowl on a hotplate I got from Goodwill. This heater is where I put the acid for a fume bluing process, or where I would heat water for the "painting" process. For now, the heater is either on or off, but adding a rheostat, or swapping out for a heater with one built in, will improve the process control here. This doesn’t have to be fancy as some people who’ve built cabinets like this have (Continued on page 14)

American Gunsmithing Association used cooking hotplates, or even just a pan over a high-wattage bulb. The plastic milk crate is used to form afire-resistant housing around the potpourri heater. Inside I fitted pieces of drywall at the bottom and around the sides. No drywall is used above the heater in order to allow air circulation. Again, I wrapped the edges with duct tape and also painted melted wax over the exposed paper sides of the drywall.

Obviously, the wax is also intended to prevent the paper from absorbing moisture. Does it occur to you that I did a good thing by using drywall as afire barrier, and then compromised that by giving it a coating of wax? And what about having plastic overhead, if the hotplate should overheat or short out and catch fire? I rational ized it this way. The hotplate is some inches away from any of the vertical walls and several inches away from the overhead plastic.

It’s entirely possible that the plastic used in the hotplate housing was molded with fire retardant additives. I’m thinking that if the plate overheated or a short occurred and ignited the housing it would burn out pretty quickly. As for the waxed paper, I suspect it would take a pretty steady, prolonged application of heat to ignite it, especially since it is closely bonded to a thick section of non-flammable gypsum.

I’m not finished worrying about those things yet, but at least those features can easily be changed if I decide to do something differently. What remains is to install various hooks and shelves to hold parts during the process. I also have some seal material that I can apply around the door. I am somewhat concerned about humidity or, worse, acid fumes escaping from the cabinet since I have a lot of tools and machinery that don’t need rust.

I would feel much better about the remote chance of fire and the accidental corrosion issue if I could operate the humidity cabinet out on my back patio, but then I would worry about curious strangers messing with it or its contents. So, I’ll run it in the garage or the basement with good air ventilation and circulation and just make it an ironclad rule to shut it off before I leave the house. What are some of the best practices in using your newly built "rust" cabinet?

Various bluing experiments and the subsequent results on a variety of metals will be written up soon! AG