Last time we looked at what rust is, now we’ll explore how to keep it away from our tools.
An excerpt from The Perfect Edge, the Ultimate Guide to Sharpening for Woodworkers:
What are we to do? Well, there are two basic approaches to rust prevention: prevent water and oxygen from coming in contact with the iron or convert the iron into another compound that is better able to resist oxygen’s efforts.
The simplest way to keep rust from eating your tools is to keep them in a place that is too dry to allow the rust reaction to get started. Woodworkers living in dry climates expend far less time and effort defeating rust than those of us in a moisture enhanced environment. You can keep your tools in a vacuum or a sealed container purged with nitrogen or containing a desiccant of some kind to absorb all the moisture. Okay, not too practical, but here at Hock Tools, less than two miles from the Pacific Ocean, we often store small parts in canning jars that we’ve pulled a vacuum on. Parts are placed into a canning jar with the lid screwed on securely but not too tight. The jar is then placed into a paint pot that’s attached to an old refrigerator compressor via the intake tube and the air is pumped out of the paint pot. The canning jar lids allow the air inside to escape but seal tightly when atmosphere is restored to the paint pot and the small blades or screws are stored in a near-total vacuum that, in one test, has held for over eight years. Not bad. Some people use a low wattage heater or a small light bulb or moisture-absorbing products in their tool box to keep it warm and/or dry.
A common rust-promoting condition that we often see is the condensation that forms when metal parts are moved from a cold place to a warm one. Warm air often holds more moisture than cold air. That moisture can condense on the surface of the cold steel forming myriad beads of “sweat” as you see on you glass of iced tea in the warm air of summer. Each of those beads is a new electrolytic cell corroding the steel beneath. Condensation can even occur when the atmosphere warms up faster than the steel parts. A chilly spring morning can warm up quickly enough to cause metal in the shop to sweat. Circulating the air can help avoid condensation but a moisture resistant coating may be necessary.
Similar to simply keeping tools away from moisture, keeping them polished can help prevent rust by eliminating surface imperfections that can trap a droplet of water, which allows rust to get started. Polished steel is not rust-proof — it still needs rust avoidance and protection measures — but shiny, polished steel tends to stay that way longer than the rough stuff.
Other methods used to prevent rust include the various things we do all the time to keep oxygen from attacking anything we care about. We apply barrier films including plating steel with other, less reactive metals such as brass, zinc or chromium or the barrier can be the paint film which protects our cars from damaging oxidization. These measures work well but as we know from experience, the slightest breach in the integrity of the film will allow rust to get started and once it starts it spreads quickly under the chrome or the paint until the coating flakes off and you have nothing left but rust.
With edged tools, we can’t tolerate a film on the cutting edge, yet that’s the part we most care about protecting: a bit of a conundrum.
A film that’s blocking the air and moisture from the steel, however, can be made from things other than paint or plating. Wax, grease, oil, etc. can all become part of the armory we enlist in the defense of our tools. The market has many products to offer and most work well, keeping in mind that some are better suited than others to one application or another.
Generally and with little effort, an edged tool can be oiled after and wiped off before each use. A protective wax coating on a machine table can also perform the double duty of keeping out moisture and allowing things to slide easily over it. The downside for these specific applications is that wax and oil require frequent maintenance and recoating. In neither of these situations would we want a coating of heavy grease, even though grease may be indicated for certain longterm storage needs. The market also offers certain oil-type products, that do a good job of displacing water on a metal surface — a real plus because rust may continue its attack if you simply coat oil over water. Water-displacing oils are formulated to drive away any moisture that may be on the surface they are coating, thus improving the protective effect.
I do not recommend silicone-based products. They work well for rust-prevention and general lubrication but can be vexing in the woodshop. Silicone seems to find its way onto everything in the shop either by contact with fingers or other carriers, or by atomization when sprayed. And, because nothing likes to stick to silicone, it will interfere with glue adhesion and finish application when and where you least expect it (so called “fisheyes” in a paint or varnish surface can be caused by a number of contaminants. Chief among them? Silicone droplets). The safest solution is
strict avoidance: do not allow silicone in your shop in the first place. Ever. Period.
The conversion defense against rust is not as simple as rust-preventative coatings; however, there are a number of rust conversion chemicals that can be applied to iron or steel that convert any iron oxide present (and it’s there even if you can’t see it) into a stable, firmly adhering layer of iron phosphate or iron tannate. These chemical converters can be painted or wiped on, some form a film that acts as a primer for additional coats of paint. It is important to note that any chemical converters that create a film are usually disqualified from edged-tool protection tasks because any coating would coat the sharp parts of our tools.
Gun bluing and Parkerizing are surface treatments that are used to rust-proof firearms. Bluing is a controlled oxidation of the iron on the surface, converting iron to a black form of iron oxide, which is a more stable molecule that occupies the same volume as the un-oxidized iron, forming a protective coating on the steel surface. Parkerizing was a brand-name electrochemical phosphate conversion coating popular until the 1940s that has been replaced by other phosphate conversion processes. Blued and Parkerized surfaces are still somewhat porous, however, and will only prevent rust if the surfaces are kept oiled, consequently, we’d best call these conversion defense methods “rust-resistant”.
In addition to chemical solutions that coat and convert a surface, there are a number of vapor phase inhibitors or volatile corrosion inhibitors (VCI) that are dry chemicals that vaporize very slowly. These chemical vapors neutralize the available ions on the steel’s surface, which prevents the interaction of oxygen with the metal, which then inhibits rust formation. VCIs are commonly available in rust preventative
wrapping papers or small containers that can be placed inside tool chests, etc. The protection is only a molecule or two thick but that’s enough to help prevent rust in enclosed, storage-type situations. When the tool-box is opened, the vapors escape of course, but they refill the space as soon as they’re closed back up again. Volatile corrosion inhibitors will eventually evaporate, so it is important to follow the manufacturer’s recommendations for periodic replacement to insure ongoing protection.
Enclosed spaces such as tool-boxes have historically been rust proofed by the addition of camphor blocks or naphthalene moth-balls. These are oilbased, solid products that sublimate (vaporize without going through the liquid phase) at low temperatures and permeate the enclosed space depositing a thin layer on the tools, which in turn protects the tools from contact with air and moisture (if you can stand the odor.)
Basically, rust prevention is achieved by either keeping your steel dry, preventing water and oxygen from contacting the tool you wish to preserve or by changing the iron to something that reacts less readily with oxygen. You can turn the iron into iron phosphate, or coat it with plating, paint, grease, wax or oil. Or, knowing that rust never sleeps — you can maintain the vigilance required too keep your tools scrupulously dry, avoiding the frustrating and time-consuming problem with rust and corrosion. Your rust-prevention efforts are part of an age-old continuum of defense against oxygen’s evil efforts to ruin our stuff — you are a member of an ancient battalion for the forces of good.
Next week: Counter-attack using chemical and electrolytic action!