Electrolytic Rust Removal - A Detailed Illustrated Tutorial, page 29
6. Conservation of Iron Artifacts - Displacing Water, Applying Sealants and Rust Inhibitors
1) Displacing Water from Iron Surface
Avoiding rusting after final rinsing is a challenge because if one does not immediately follow up with the water-displacing treatment, the iron object will re-rust before there is a chance to dry it completely. Drying may be an optional step when the artifact's surface is sealed with hot wax, which is heated above the boiling point of water. In this case, the moisture absorbed by the artifact easily evaporates.
There are a few ways of dehydrating iron artifacts: solvent dehydration, heat drying, or vacuum desiccation. In my opinion, the solvent dehydration technique is the most effective than any other methods. For instance, with the heat drying (ovens or infra-red lamps), a wet iron object that is exposed to air will turn rusty again as soon as it dries off.
The solvent dehydration can be done with a water-miscible solvent, Ethanol, Methanol, Isopropanol, Methylated Spirits, Pure Alcohol, and Acetone. My favorite is Acetone as long as the acetone bath is placed outdoors or in a well ventilated area. And the acetone dehydration should follow the final rinsing immediately.
Acetone is capable of dissolving certain plastics. So, not to be negatively surprised, and to be on a safe side, use an enameled container for the acetone bath.
Use Enameled Pan for Dehydrating Derusted Artefact in Acetone
Acetone neutralizes chlorides and salts as well as attaches to water molecules; thus, getting all the water out of the derusted iron object completely. Submersing your iron artifact for 30 seconds will be enough to complete the dehydration project.
Solvents can be dangerous if inhaled or handled, so the solvent dehydrating procedure should be conducted outside, with adequate protection, and according to the instructions given for any specific solvent used. Ethanol and acetone are the most effective but are toxic and have lower flash points.
2) Sealants for Iron Conservation and Preservation
Once the iron artifact has been taken out of the acetone bath, and acetone has evaporated, contact with air should be minimized before the artifact's surface is given the final sealant or insulating coating. This protective layer insulates the iron from the effects of moisture, chemically active vapors, and gases (oxygen especially).
In general, the sealant selected should be:
1) impermeable to water vapors and gases
2) natural-looking, so that it does not detract from the appearance of the artifact
3) reversible, so it could be replenished or replaced
4) transparent or semitransparent, so any corrosion of the metal surface can be quickly detected
Depending on what you have planned to do with your iron artifact, you can treat it with any of the following proven-to-be-effective sealants for iron conservation:
WD-40, Light Oils, Tannic Acid and Rust Converters
For QUICK PROTECTION against oxygen and moisture, cover the artifact with a generous coating of WD-40, or light oil, which can be easily removed by solvents if necessary. If you do not plan to use the longer-lasting sealants, reapply WD-40 or light oils once in two months. The derusted tools get the same treatment + some humidity reduction techniques.
You may want to cover the artifact with two to three thin coats of tannic acid - the active ingredient in products like rust converters, which halts and prevents any further rusting. The tannic acid dries pretty quick, but you should let the final coat dry overnight if you are going to paint the artifact afterwards.
Rust converters are not designed to remove the rust but to convert unstable corrosion into a stable, protective layer with the help of a latex-based coating. "Rust-Oleum" (or "Rustoleum") is one of those commercial products, and it is not reversible - it can only be removed with Sodium Hydroxide.
Rust Inhibitors
For LONG PROTECTION indoors and outdoors, apply Rust Inhibitors (or Corrosion Inhibitors). They are designed especially to protect the bare-metal iron surfaces; thus, best serving the purpose of protecting the freshly electrolyzed iron artifacts. Being brush-on or spray-on products, the rust inhibitors are easy to apply; however, most of them will darken the surface of the artifact, and, therefore, are not appropriate for all cases.
Application of any rust inhibitor must be carried out in a well ventilated area (or better - outdoors!), especially when it takes a couple of days for the product to dry.
Briwax
For LONG PROTECTION indoors, apply the Briwax method (Waxing). Briwax is a solvent based blend of beeswax and carnauba wax (also called Brazil wax and palm wax). It usually comes in the form of hard yellow-brown flakes. Briwax seals up the pores, and if there is any rust on the iron surface, no further rusting will occur - the rust will be sealed as well.
An iron artifact must be dehydrated prior to using the Briwax. Before applying the Briwax, first heat the artifact with a hair dryer (or infra-red lamp) until the relic is very warm but not too hot. Then the Briwax is applied in a thin layer with a clean cloth, covering the artifact completely. Let the artifact cool a little, and then buff the Briwax out with a rag or bristle brush (a shoe polish brush best serves the purpose). Add more layers of Briwax until you are satisfied with your relic's appearance. Always buff between applications.
Briwax may be not an appropriate coating for all metal surfaces, especially where it is impossible to cover the artifact completely, or where the slightly glossy finish would be inappropriate.
Microcrystalline Wax
For LONGER PROTECTION both indoors and outdoors, Microcrystalline Wax, such as Cosmoloid 80H (not available in the US), and its substitutes - Gulf 75 Micro-Wax and Witco180M, best satisfy the requirements of the iron artifact conservation. The microcrystalline waxes have a high melting point, are relatively hard, inert, and will not yellow over time. And out of all sealants commonly used, they are the least permeable to water vapor. The microcrystalline wax can be easily removed by placing the artifact in boiling water.
After being taken out of the rinse water, and, without drying, an iron artifact can be promptly placed in a vat of microcrystalline wax that has been heated to 175°C - well above the boiling point of water. The artifact must be kept in the wax at this high temperature until the water is completely vaporized (bubbles stop evolving from the artifact). This may take a few days for large artifacts. After the iron surface has absorbed enough wax, and all the water has been evaporated, the wax bath is cooled to 95°C, the artifact is taken out, and the excess wax is immediately wiped off.
The microcrystalline wax is the best sealant for both cast-iron and wrought-iron artifacts. Mixed with graphite, the microcrystalline wax can be used for covering the surface defects caused by heavy rust; thus, enhancing the relic's appearance. When applied to the iron object, the microcrystalline wax provides considerable stability and strength to it - this is very useful for consolidating the fragile iron relics.
Polyurethane-Based Paints
For LONG PROTECTION of iron objects that are to be displayed OUTDOORS, and cannot be treated with microcrystalline wax, paint them with the most recommended Polyurethane-Based Paints (like the polyurethane varnishes) - "rust paints". Only keep in mind that polyurethane is not reversible, and to be removed, it must be sandblasted off.
If you plan to paint your iron object with conventional metal paint, first apply a coat of primer as soon as possible before painting. This would greatly reduce any chance of rust forming under the paint; however, badly applied lacquer or paint can lead to worse rusting.
On the market (Hardware and Auto Parts Stores) today, there is a great number of various sealants - monomers, acrylates, acetates, epoxies, paints, oils, lacquers, etc. And many of them are irreversible, highly permeable to moisture, or they just craze and peel.
The sealants I suggested above have withstood the test of time. But one should keep in mind that no single sealant is 100% successful, and all have "pros" and "cons". So choose the one according to your needs.
For conservation and preservation of the de-rusted artifact in my tutorial, I chose what I had at hand - a rust inhibitor, and it well served the purpose.