Metal Blackening

Many of you may not be familiar with this finish.  However, it is more likely you simply didn’t realize this is what you were seeing. One of the most common examples I can think of, that most of you are familiar with, is Allen Head bolts, and often factory fender bolts etc.

Metal Blackening dates back in time, almost as far as the first metal workers. In its origins, it was a fairly lengthy, and hazardous process to the workers, and to the environment, and usually required a large complicated facility to impart. Originally, steel was blackened using a heat process. Now, chemical process, or a combination of the methods can be used.

There are two oxides in steel: red and black.
Red oxide (bad) which we know as rust, is corrosive and destructive.
Black oxide (good) is a protective, abrasion-resistant surface material that prevents rust.

Simply put, blackening, makes the surface of metal of a porous nature, protective in its self, but, also capable of ‘absorbing’ and retaining a film of oil or other protective material, such as a clear sealant.

CHEMICAL BLACKENING

Here are a few bolts, nuts and washers I chemically blackened. As you can see, the end result is very much a factory uniform result.

The beauty of a chemical blackening is that, it is of minimal hazard, and extremely fast, taking only a matter of seconds, to a maximum of a few minutes.  The size of items to be blackened is limited only by the size of container used to hold the blackening solution (chemicals).

The solution can also be swabbed or brushed directly on to handle larger items, to blacken a surface without removal, or to perform touch ups.

While the the chemical blends involved vary somewhat from one supplier to another, they are essentially comprised of blends of Inorganic and/or Organic Acids, copper and nickel compounds.

You’ll Need some very basic supplies and safety equipment.  While chemical blackening is not particularly hazardous, it is always prudent to use basic eye and hand protection when dealing with any chemical process.

Chemical blackening requires a clean part to start with, and either an oil or sealant for completion.

-Have several soft cloths and Acetone for cleaning parts.
-Petroleum-based penetrating oil for tools
OR
-Vegetable based oil for items that come in contact with food
OR
-Clear sealant finish.

First clean the item using acetone and a soft cloth to remove dust, oils and other contaminants.
Paper towel works well to ‘blot’ the surface dry after cleaning.

Immerse the item into the chemical solution.

Keep the item submerged for from 30 seconds, to no more than 3 minutes, then remove and wipe dry.

If treating an item that can not be submerged, a brush or swab can be used to apply the chemical directly to the item and keep the part saturated until the desired finish is achieved.

Optionally, clean the item again with acetone.
Allow the item to air dry for at least 30 minutes to ensure any chemical residue evaporates from the blackened surface.

Next, spray the item with oil or sealant and allow to soak for a couple minutes, then wipe away any excess with a clean rag.

You’re Done!

Suppliers of chemical blackening kits and solutions are;

Caswell Inc

The beauty of the Caswell ‘kit’, is that it provides everything you need, and you provide distilled water to mix the chemicals into.  This saves on shipping costs by reducing weight and volume.  Starting at about $45, you get a kit capable of over 1 gallon of blackening solution delivered to your door.  When your solution weakens, you can simply add the supplied chemical to it to extend it’s life indefinetly, further reducing your end cost.  Kits are available up to 45 gallon capacity for your really large items.  Caswell also has kits available to blacken Stainlesss Steel and has sealing solutions as well.  Caswell has outlets in both Canada and the USA.

EASTWOOD

Long standing in the Automotive restoration community, US based Eastwood, has developed its own premixed solution.  Small kits, start at $40, which include the basic container, solution, clear sealer and gloves to get started.  Additional solution is available, starting at $17 per pint.  If you don’t need a container, you can simply order a bottle of solution, and imerse items, or wipe it on.  As this system is pre mixed, there is nothing else required from you, it’s ready right out of the bottle.  Shipping costs are a little higher due to the pre-mixed solution.

HEAT INDUCED BLACKENING (non-chemical)

You’ll Need some very basic supplies, and a little time.
Heat blackening requires a clean part to start with, and either oil or sealant on completion.
-Several soft cloths, Acetone, Petroleum-based penetrating oil
-For the more hazardous process of Heat Blackening, you’ll require additional safety equipment.
-Face shield, protective clothing including heavy leather work gloves
-A small torch for heating items, and a polyester scrub pad
-Petroleum-based penetrating oil for tools
OR
-Vegetable based oil for items that come in contact with food
OR
-Clear sealant finish.

First clean the item using acetone and a soft cloth to remove dust, oils and other contaminants.
Paper towel works well to ‘blot’ the surface dry after cleaning.

NOTE: If the item is used for any food handling process, use vegetable oil instead of petroleum based oil and use a stove or oven to heat the item for one hour at temperatures below 550 degrees Fahrenheit (vegetable oil has a flash point of 600 degrees Fahrenheit).

Otherwise, proceed as follows.

Dip or wipe the entire item with a thin coating of petroleum-based penetrating oil.
Work outdoors, or in a well-ventilated area, with shop doors and windows open.
Wear protective clothing, full face shield, and leather gloves.
Heat the item with a torch until it begins to smoke and turn black.

Next, spray the item until it is dripping wet with penetrating oil.
Heat the item again until it begins to smoke.
The petroleum molecules will react with the molecules of heated steel to form a chemical bond, thus sealing the metal.

Allow the item to cool to room temperature for at least 60 minutes.
Once cool, wipe the item down with acetone and a polyester scrub pad to remove any remaining burnt oil.

Spray the item with penetrating oil or sealant and wipe away any excess with clean rags.

You’re Done!

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