Aging & Patinas
At Twisted Metalcraft, we custom fabricate from nearly any metal & alloy, which can be coloured, aged or have a patina applied.
Twisted Metalcraft can do this by means of abrasion, applying Acid / Alkaline which can be dipped, swabbed, wiped or even buried using techniques that can take anywhere from a minute to weeks to complete. In some cases they can even be left to naturally age, which can take many years.
Colouration can even be achieved by applying heat and watching the transformation happen instantly before your eyes.
Aging and colouring of steel and alloys has been done for hundreds of years to create life-likeness and give character to sculptures and other metal fabricated items. It has been used to unify and to enhance the decorative aspects of the sculpture or work pieces.
At Twisted Metalcraft, we believe colour is a key factor in the visual coherence and significance of objects. It is used as a means of expression and therefore it is of the upmost importance.
For more information on aging and metal finishes please see our Architectural & Bespoke Metal Finishes Page.
Why Stainless Steel?
Stainless steel’s resistance to corrosion and staining, relatively low maintenance and familiar lustre make it an ideal material for many applications. There are many grades of stainless steel, of which fifteen are most commonly used.
The alloy is milled into coils, sheets, plates, bars, wire, and tubing to be used in cookware, cutlery, household hardware, surgical instruments, major appliances, industrial equipment (for example, in sugar refineries), as an automotive and aerospace structural alloy and construction material in large buildings.
Storage tanks and tankers, used to transport orange juice and other food, are often made of stainless steel because of its corrosion resistance. This also influences its use in commercial kitchens and food processing plants, as it can be steam-cleaned and sterilized and does not need paint or other surface finishes.
Stainless Steel General Information
In metallurgy, stainless steel is defined as a steel alloy with a minimum of 11% chromium content by mass.
Stainless steel does not stain, corrode, or rust as easily as ordinary steel;
it “stains less” but it is not stain-proof. It is also called corrosion-resistant steel, when the alloy type and grade are not detailed, particularly in the aviation industry.
There are different grades and surface finishes of stainless steel to suit the environment to which the material will be subjected in its lifetime.
Common uses of stainless steel are cutlery and watch straps.
Stainless steel differs from carbon steel by the amount of chromium present. Carbon steel rusts when exposed to air and moisture. Rust is an iron oxide film which is active and accelerates corrosion by forming more iron oxide.
Stainless steels have sufficient amounts of chromium present so that a passive film of chromium oxide forms which prevents further surface corrosion and blocks corrosion from spreading into the metal’s internal structure.
Stainless steel is used for buildings for both practical and aesthetic reasons. Stainless steel was in vogue during the art deco period. The most famous example of this is the upper portion of the Chrysler Building.
Some diners and fast-food restaurants use large ornamental panels and stainless fixtures and furniture. Because of the durability of the material, many of these buildings retain their original appearance.
Other uses of Stainless Steel
Stainless steel uses are nearly limitless.
In the home, stainless steels are used in the production of dish ware and other cutlery, dinner service, pots and cooking utensils, kitchen sinks, stoves and outdoor barbecue’s, gardening tools and furnishings.
In cities and towns, stainless steel is used in building facades, bus shelters, lifts and escalators, phone booths, other street fixtures and subway cars and station equipment.
In industry, stainless steel uses include making tools for the creating of pharmaceuticals and food products, industrial plants for the management of drinkable and waste water, chemical and petrochemical plants, automotive and aeroplane engine parts and petroleum and chemical tankers.
The corrosion resistance of iron-chromium alloys was first recognized in 1821 by the French metallurgist Pierre Berthier, who noted their resistance against attack by some acids and suggested their use in cutlery.
Metallurgists of the 19th century, however, were unable to produce the combination of low carbon and high chromium found in most modern stainless steels and the high-chromium alloys they could produce were too brittle to be practical.
In the late 1890s, Hans Goldschmidt of Germany developed an aluminothermic (thermite) process for producing carbon-free chromium. In the years 1904–1911 several researchers, particularly Leon Guillet of France, prepared alloys that would today be considered stainless steel.
In 1912, Elwood Haynes applied for a U.S. patent on a martensitic stainless steel alloy. This patent was not granted until 1919.
Also in 1912, Harry Brearley (of the Brown-Firth research laboratory in Sheffield, England), while seeking an erosion-resistant alloy for gun barrels, discovered and subsequently industrialized a martensitic stainless steel alloy.
The discovery was announced two years later in a January 1915 newspaper article in The New York Times.
Brearly applied for a U.S. patent during 1915. This was later marketed under the “Staybrite” brand by Firth Vickers in England and was used for the new entrance canopy for the Savoy Hotel in 1929 in London.
Cleaning Stainless Steel
Cleaning Stainless Steel can be easy if the right steps and precautions are taken. Below we will explain a few do’s and don’ts when it comes to cleaning Stainless Steel.
Stainless Steel Should be cleaned regularly to prevent the build up of dirt and chemicals that can cause stains.
As the name of Stainless Steel suggests, it will Stain-Less but, it is not Stain-Proof.
Stainless Steel is protected from corrosion by a thin layer of chromium oxide.
This Oxide layer is created by the presence of Oxygen in the atmosphere combining with the Chromium on the surface of the Stainless Steel. Any contamination on the surface of the steel hinders this process and reduces or destroys this protective barrier which is why routine cleaning should be done.
To start off, you do not need to go out and buy expensive Stainless specific cleaners. These do work very well, however if you are not cleaning Stainless every day or would like to save a pretty penny you don’t need them.
Use of Mild Detergent that has been diluted in warm water, along with a soft cloth or brush, is generally all that is needed to get the surface clean again. Only a small amount of Mild detergent should be used; a stronger detergent will require a lot more water to remove the residue left behind.
Clean regularly and remember to wipe the surface dry straight away to avoid spotting on the surface.
Depending on the extent of cleaning required you may need to use something stronger and in this case it is recommended that you use methylated spirits or glass cleaner on a soft cloth (this is great for removing finger prints).
For a longer lasting protection olive oil can be used with a soft cloth. Be sure to use the olive oil sparingly, as if too much is used, dust will stick and accumulate on the surface.
For best results cleaning Stainless with a grain or satin finish, clean with the grain not against it.
Removing stains and Labels
Food or coffee stained items should be left to soak in a solution of boiling water and Bi-Carb Soda (otherwise known as Baking Soda).
To remove sticky labels, a hair dryer can be used to soften the glue for easy removal (rather than using a scraper as this will scratch the steel).
Once this is done a soft cloth soaked with olive oil and a little elbow grease will get the job done.
Using a mere wet cloth to clean Stainless Steel does nothing but smear the dirt over the surface.
Do not leave Stainless Steel in contact with Acids, Alkalies, Salts or Carbon Steels (wet or not) for prolonged periods of time as this will discolour or stain your item (as the name suggests it is Stain-Less not Stain-Proof).
Never use steel unless it states it is ok to use on Stainless Steel.
Steel wool is usually made up of carbon steel and any of these particles can be embedded into your Stainless only to rust later on down the track.
Working with Stainless Steel
Stainless steel distorts up to 70% more than other steels when heat is applied, therefore much more care should be taken when welding, cutting, and polishing.
When welding stainless steel be sure to aim the heat away from the job and remember to use chill bars, or even cool the work with water.
Cutting stainless steel for the average person should be done using an angle grinder with a 1mm thick cutting disk.
Remember the thinner the disk the better, as this will cut through a lot easier.
A thicker cutting disk will only add more heat and it will harden the steel making your job of cutting the steel more difficult with a possibly burning your work.
Drilling is a cutting process and therefore very different to grinding processes, unlike grinding where you are using friction and speed, with drilling you should use a slow speed, sharp drill bit and plenty of lubricant. Drilling in this way will prolong the life of your drill bits and not burn your job.
Remember as mentioned above, the hotter Stainless Steel gets the harder it becomes, the harder it becomes the easier it will blunten your drill bits.
Bending stainless can be a little difficult, as it work hardens very quickly. After only a few bends the steel forms cracks and will break easily.
Any steel will expand when heated and contract when cooled.
It is important to know that the steel will expand or contract in a uniform manner, for example, if you were to apply heat to a ring of steel it will expand in a way that will increase the outer as well as the inner circumference and the opposite would occur if cooled.
Chemical properties of stainless steel
High oxidation-resistance in air at ambient temperature are normally achieved with additions of a minimum of 13% (by weight) chromium, and up to 26% is used for harsh environments.
The chromium forms a passivation layer of chromium(III) oxide (Cr2O3) when exposed to oxygen. The layer is too thin to be visible and the metal remains lustrous. It is impervious to water and air, protecting the metal beneath.
Also, this layer quickly reforms when the surface is scratched. This phenomenon is called passivation and is seen in other metals, such as aluminium and titanium. Corrosion resistance can however be adversely affected if the component is used in a non-oxygenated environment, a typical example being underwater keel-bolts buried in timber.
When stainless steel parts such as nuts and bolts are forced together, the oxide layer can be scraped off causing the parts to weld together.
When disassembled, the welded material may be torn and pitted, an effect that is known as galling. This destructive galling can be best avoided by the use of dissimilar materials, e.g. bronze to stainless steel, or even different types of stainless steels (martensitic against austenitic, etc.), when metal-to-metal wear is a concern.
In addition, Nitronic alloys (trademark of Armco, Inc.) reduce the tendency to gall through selective alloying with manganese and nitrogen.
Nickel also contributes to passivation, as do other less commonly used ingredients such as molybdenum and vanadium.
Stainless Steel Applications
Stainless steel’s resistance to corrosion and staining, low maintenance, relatively low cost, and familiar luster make it an ideal base material for a host of commercial applications.
There are over 150 grades of stainless steel, of which fifteen are most common.
The alloy is milled into coils, sheets, plates, bars, wire, and tubing to be used in cookware, cutlery, hardware, surgical instruments, major appliances, industrial equipment, and as an automotive and aerospace structural alloy and construction material in large buildings.
Storage tanks and tankers used to transport orange juice and other food are often made of stainless steel, due to its corrosion resistance and antibacterial properties. This also influences its use in commercial kitchens and food processing plants, as it can be steam cleaned, sterilized, and does not need painting or application of other surface finishes.
Stainless steel is also used for jewellery and watches. The most common stainless steel alloy used for this is 316L. It can be re-finished by any jeweller and will not oxidize or turn black.
Some firearms incorporate stainless steel components as an alternative to blued or parkerized steel.
A few, more expensive revolvers (like the Smith and Wesson Model 60) and pistols (like versions of the Colt M1911) are milled entirely from stainless steel.
This gives a high-luster finish similar in appearance to nickel plating; but, unlike plating, the finish is not subject to flaking, peeling, wear-off due to rubbing (as when repeatedly removed from a holster over the course of time), or rust when scratched.
Recycling & reuse
Stainless steel is 100% recyclable.
In fact, an average stainless steel object is composed of about 60% recycled material, 25% originating from end-of-life products and 35% coming from manufacturing processes.
Types of stainless steel
There are different types of stainless steels. When nickel is added, for instance, the austenite structure of iron is stabilized. This crystal structure makes such steels non-magnetic and less brittle at low temperatures.
For greater hardness and strength, carbon is added.
When subjected to adequate heat treatment, these steels are used as razor blades, cutlery, tools, etc.
Significant quantities of manganese have been used in many stainless steel compositions. Manganese preserves an austenitic structure in the steel as does nickel, but at a lower cost.
Stainless steels are also classified by their crystalline structure:
Austenitic, or 300 series, stainless steels comprise over 70% of total stainless steel production. They contain a maximum of 0.15% carbon, a minimum of 16% chromium and sufficient nickel and/or manganese to retain an austenitic structure at all temperatures from the cryogenic region to the melting point of the alloy.
A typical composition of 18% chromium and 10% nickel, commonly known as 18/10 stainless, is often used in flatware. Similarly, 18/0 and 18/8 are also available.
Super austenitic stainless steels, such as alloy AL-6XN and 254SMO, exhibit great resistance to chloride pitting and crevice corrosion due to high molybdenum content (>6%) and nitrogen additions. The higher nickel content ensures better resistance to stress-corrosion cracking versus the 300 series.
The higher alloy content of super austenitic steels makes them more expensive. Other steels can offer similar performance at lower cost and are preferred in certain applications.
Low carbon versions of the Austenitic Stainless Steel, for example 316L or 304L, are used to avoid corrosion problems caused by welding. The “L” means that the carbon content of the Stainless Steel is below 0.03%. This will reduce the sensitization effect and precipitation of Chromium Carbides at grain boundaries, due to the high temperature produced by welding operation.
Ferritic stainless steels are highly corrosion-resistant, but less durable than austenitic grades.
They contain between 10.5% and 27% chromium and very little nickel, if any, but some types can contain lead.
Most compositions include molybdenum; some, aluminium or titanium.
Common ferritic grades include 18Cr-2Mo, 26Cr-1Mo, 29Cr-4Mo, and 29Cr-4Mo-2Ni. These alloys can be degraded by the presence of σ chromium, a intermetallic phase which can precipitate upon welding.
Martensitic stainless steels are not as corrosion-resistant as the other two classes but are extremely strong and tough, as well as highly machineable and can be hardened by heat treatment.
Martensitic stainless steel contains chromium (12-14%), molybdenum (0.2-1%), nickel (0-<2%), and carbon (about 0.1-1%), giving it more hardness but making the material a bit more brittle. It is quenched and magnetic.
Precipitation-hardening martensitic stainless steels have corrosion resistance comparable to austenitic varieties, but can be precipitation hardened to even higher strengths than the other martensitic grades.
The most common, 17-4PH, uses about 17% chromium and 4% nickel.
There is a rising trend in defense budgets to opt for an ultra-high-strength stainless steel when possible in new projects, as it is estimated that 2% of the US GDP is spent dealing with corrosion.
The Lockheed-Martin Joint Strike Fighter is the first aircraft to use a precipitation-hardenable stainless steel—Carpenter Custom 465—in its airframe.
Duplex stainless steels have a mixed microstructure of austenite and ferrite; the aim being to produce a 50/50 mix, although in commercial alloys the mix may be 40/60 respectively.
Duplex steels have improved strength over austenitic stainless steels and also improved resistance to localised corrosion, particularly pitting, crevice corrosion and stress corrosion cracking.
They are characterised by high chromium (19–28%) and molybdenum (up to 5%) and lower nickel contents than austenitic stainless steels.
The most used Duplex Stainless Steel are the 2205 (22% Chromium, 5% Nickel) and 2507 (25% Chromium, 7% Nickel); the 2507 is also known as “SuperDuplex” due to its higher corrosion resistance.
Stainless grades and specs
100 Series—austenitic chromium-nickel-manganese alloys
Type 101—austenitic that is hardenable through cold working for furniture
Type 102—austenitic general purpose stainless steel working for furniture
200 Series—austenitic chromium-nickel-manganese alloys
Type 201—austenitic that is hardenable through cold working
Type 202—austenitic general purpose stainless steel
300 Series—austenitic chromium-nickel alloys
Type 301—highly ductile, for formed products. Also hardens rapidly during mechanical working. Good weldability. Better wear resistance and fatigue strength than 304.
Type 302—same corrosion resistance as 304, with slightly higher strength due to additional carbon.
Type 303—free machining version of 304 via addition of sulfur and phosphorus. Also referred to as “A1” in accordance with.
Type 304—the most common grade; the classic 18/8 stainless steel. Also referred to as “A2” in accordance with ISO 3506.
Type 304L— same as the 304 grade but contains less carbon to increase weldability. Is slightly weaker than 304.
Type 304LN—same as 304L, but also nitrogen is added to obtain a much higher yield and tensile strength than 304L.
Type 308—used as the filler metal when welding 304
Type 309—better temperature resistance than 304, also sometimes used as filler metal when welding dissimilar steels, along with inconel.
Type 316—the second most common grade (after 304); for food and surgical stainless steel uses; alloy addition of molybdenum prevents specific forms of corrosion. It is also known as marine grade stainless steel due to its increased resistance to chloride corrosion compared to type 304. 316 is often used for building nuclear reprocessing plants.
Type 316L—extra low carbon grade of 316, generally used in stainless steel watches and marine applications due to its high resistance to corrosion. Also referred to as “A4” in accordance with ISO 3506.
Type 316Ti—includes titanium for heat resistance, therefore it is used in flexible chimney liners.
Type 321—similar to 304 but lower risk of weld decay due to addition of titanium. See also 347 with addition of niobium for desensitization during welding.
400 Series—ferritic and martensitic chromium alloys
Type 405— ferritic for welding applications
Type 408—heat-resistant; poor corrosion resistance; 11% chromium, 8% nickel.
Type 409—cheapest type; used for automobile exhausts; ferritic (iron/chromium only).
Type 410—martensitic (high-strength iron/chromium). Wear-resistant, but less corrosion-resistant.
Type 416—easy to machine due to additional sulfur
Type 420—Cutlery Grade martensitic; similar to the Brearley’s original rustless steel. Excellent polishability.
Type 430—decorative, e.g., for automotive trim; ferritic. Good formability, but with reduced temperature and corrosion resistance.
Type 439—ferritic grade, a higher grade version of 409 used for catalytic converter exhaust sections. Increased chromium for improved high temperature corrosion/oxidation resistance.
Type 440—a higher grade of cutlery steel, with more carbon, allowing for much better edge retention when properly heat-treated. It can be hardened to approximately Rockwell 58 hardness, making it one of the hardest stainless steels. Due to its toughness and relatively low cost, most display-only and replica swords or knives are made of 440 stainless. Also known as razor blade steel. Available in four grades: 440A, 440B, 440C, and the uncommon 440F (free machinable). 440A, having the least amount of carbon in it, is the most stain-resistant; 440C, having the most, is the strongest and is usually considered more desirable in knifemaking than 440A, except for diving or other salt-water applications.
Type 446—For elevated temperature service
500 Series—heat-resisting chromium alloys
600 Series—martensitic precipitation hardening alloys
601 through 604: Martensitic low-alloy steels.
610 through 613: Martensitic secondary hardening steels.
614 through 619: Martensitic chromium steels.
630 through 635: Semiaustenitic and martensitic precipitation-hardening stainless steels.
Type 630 is most common PH stainless, better known as 17-4; 17% chromium, 4% nickel.
650 through 653: Austenitic steels strengthened by hot/cold work.
660 through 665: Austenitic superalloys; all grades except alloy 661 are strengthened by second-phase precipitation.
Type 2205— the most widely used duplex (ferritic/austenitic) stainless steel grade. It has both excellent corrosion resistance and high strength.
Brass is a binary alloy composed of copper and zinc that has been produced for millennia and is valued for its workability, hardness, corrosion resistance and attractive appearance.
The exact properties of different brasses depend on the composition of the brass alloy, particularly the copper-zinc ratio.
In general, however, all brasses are valued for their machinability, or the ease with which the metal can be formed into desired shapes and forms while retaining high strength.
While there are differences between brasses with high and low zinc contents, all brasses are considered malleable and ductile (low zinc brasses more so).
Due to its low melting point, brass can also be cast relatively easily; however, for casting applications, a high zinc content is usually preferred.
Brasses with a lower zinc content can be easily cold worked, welded and brazed.
A high copper content also allows the metal to form a protective oxide layer (patina) on its surface that guards against further corrosion; a valuable property in applications that expose the metal to moisture and weathering.
The metal has both good heat and electrical conductivity (it’s electrical conductivity can from 23% to 44% that of pure copper), and it is wear and spark resistant.
Like copper, its bacteriostatic properties have resulted in its use in bathroom fixtures and healthcare facilities.
Brass is considered a low friction and non-magnetic alloy, while its acoustic properties have resulted in its use in many ‘brass band’ musical instruments.
Artists and architects value the metal’s aesthetic properties, as it can be produced in a range of colours, from deep red to golden yellow.
Copper-zinc alloys were produced as early the 5th century BC in China and were widely used in central Asia by the 2nd and 3rd century BC.
These decorative metal pieces, however, can be best referred to as ‘natural alloys’, as there is no evidence that their producers consciously alloyed copper and zinc. Instead, it is likely that the alloys were smelted from zinc-rich copper ores, producing crude brass-like metals.
Brass Cleaning & Care
True brass is an alloy of copper and zinc. It tends to oxidize (tarnish) quickly when exposed to air, which is a major reason why most brass is given a clear coating of lacquer to prevent this condition.
Most conventional polishes such as “Brasso®,” “Twinkle®,” etc. coat the raw metal with a thin film of oil to help inhibit future tarnishing. Additionally, most metal polishes contain solvents and detergents to remove the tarnish, mild abrasives to polish the metal, and oils to act as a barrier.
Many people over-use and flood metal surfaces with polishes believing that they are better protecting the surface. The more polish, the more protection.
Wrong assumption. More polish creates a smudging problem since fingerprints (human body oils) “dissolve” the solvency of the metal polish.
Additionally, too much polish may discolour the surface.
Only a trace amount creating a thin film should be applied. Therefore, an adequate amount of metal polish should be applied and spread out an amount on an absorbent rag. Then, let the rag dry out for a minimum of 24 hours before placement onto most metals.
Apply this trace amount of polish with the grain of the brass with one hand while buffing it out in a rapid motion (creating friction) with the other hand. This burnishing action will harden the polish (like “spit shining” a shoe) and create a surface far more difficult to smudge or discolour.
Cleaning (for light soils): The use of isopropyl (rubbing alcohol) applied with the sponge side of a light-duty, “white-padded” scrubbing sponge with the grain of the brass. In the event of tougher scuff marks, flip over sponge and gently agitate with the grain of the metal with the white scrub pad. For heavier soils: Dampen sponge side with water, and apply a light scouring low abrasion creme onto it. Work product into sponge, and then stroke it onto your brass with the grain. Once completed, wipe surface thoroughly clean with a clean, soft rag. Once surface is cleaned, then go to the next step.
Polishing: One of the best tools which provides just the right amount of oil onto metal is a “yellow” treated dust cloth. Wipe down brass with this cloth and then buff it dry with a soft, cotton cloth. This trace amount of oil in the cloth should not smear or discolour, especially after buffing.
Olive Oil. Brass will look brighter and require less polishing if rubbed with a cloth moistened with olive oil after each polishing. Olive oil retards tarnish.
After the Copper Age came the Bronze Age, followed later by the Iron Age. The Reason there was not a ‘Brass Age’ is because, for many years, it was extremely difficult to manufacture.
Before the 18th century, zinc metals couldn’t be made because it melts at 420ºC and boils at about 950ºC, this is below the temperature that is needed to reduce the zinc oxide with charcoal. Without native zinc, brass was made by mixing ground smithsonite ore with copper and heating the mixture in a crucible.
Using this method, the heat was sufficient enough to reduce the ore to a metallic state without melting the copper. In this process the vapor from the zinc passes through the copper to form brass, which was then melted to create a uniform alloy.
Only in the last thousand years has brass been appreciated as an engineering alloy. Initially, bronze was easier to make using native copper and tin and it was an ideal alloy for making utensils.
Egyptians knew copper very well and it was represented by the ankh symbol ‘C’ also used to denote eternal life in their hieroglyphs. Even though tin was readily available for making bronze, brass was rarely used except where its golden colour and lustre was sought after.
The Greeks word for brass is ‘oreichalcos’, a brilliant and white copper.
Romans sought after and used brass especially for the production of gold coloured helmets. The Romans used grades of Brass containing from 11 to 28 per cent of zinc to obtain decorative colours for all types of ornamental jewellery.
When the Brass had to be formed into difficult shapes and excessively worked the metal had to be very malleable and the composition they preferred was around 18%, nearly that of the 80/20 gilding metal still in demand today.
In medieval times, pure zinc could not be sourced.
The centre of the worlds copper supply was in Swansea, in South Wales.
Brass was made in Britain from calamine that was found in the Mendip hills of Somerset.
Other brass manufacturers of Germany, Sweden, Holland and China, had a good reputation for their quality.
Brass was commonly used in the manufacture of plates that were inscribed to commemorate the dead and used in church monuments. These typically contained 23-29% of zinc, often using small quantities of lead and tin as well.
Brass had also become the standard alloy that all accurate instruments, such as clocks, watches and navigational aids were made.
The invention of the chronometer by Harrison in 1761 relied on the use of brass for the timekeeper that won him a prize of £20,000. These Properties took a lot of the guesswork out of marine navigation, and therefore saved many lives.
There are still today many examples of clocks from the 17th and 18th centuries that are still in good working order.
Copper is a chemical element with the symbol Cu which is from the Latin word Cuprum.
Copper has an atomic number of 29 and is known for its soft, malleable, and ductile properties.
It also has very high electrical and thermal conductivity.
The first metal ever manipulated and worked with by humans was copper.
This metal was known for its reddish shiny appearance. Copper is still a vitally important metal today.
The oldest known copper object was found in the Middle East. It was a small Awl (Used for stitching) buried with a middle aged woman. This artifact was dated back as far as 5100 B.C.
The U.S. penny was originally made of pure copper. It is now made of 97.5 percent zinc with a thin copper plating.
Copper ranks as the 3rd most consumed industrial metal in the world today, first and second place is made up of iron and aluminium.
Roughly three quarters of refined copper goes into the manufacture of electrical wires, communication cables and electronics.
Apart from gold, copper is the only metal on the periodic table that isn’t naturally silver or grey in colour.
Facts about Copper
Atomic number (number of protons): 29
Atomic symbol: Cu
Atomic weight: 63.55
Density: 8.92 grams per cubic centimetre
Phase at room temperature: Solid
Melting point: 1,984.32 degrees Fahrenheit (1,084.62 degrees Celsius)
Boiling point: 5,301 degrees F (2,927 degrees C)
We need copper in our diets. Copper is an essential trace mineral. It is crucial for forming red blood cells in the body. Fortunately, almost everyone gets enough copper in their diet from foods such as leafy greens, beans, potatoes and grains.
Having too much copper in your diet is not good. Ingesting high levels of the metal can cause vomiting, abdominal pain and jaundice.
Copper has antimicrobial properties and kills bacteria, yeasts and viruses on contact. For more information on the antimicrobial properties of copper, please see our information on Antimicrobial Copper Page.
Early Copper Development & Uses
About two thirds of the copper found on earth is found in igneous rocks (volcanic rocks) and about a quarter is found in sedimentary rocks (earth and rock worn down by water).
Copper is smelted and purified before use, the smelting process was used from about 4500 B.C. Copper is found in ores commonly orange & green in colour from decay and impurity’s.
Many years later the next technological development was creating copper alloys, the first of which was Bronze; this ushered in the bronze age.
Copper artifacts have been found all over the world from many ages.
In ancient Egypt people used copper to make jewellery and it was considered the metal of the gods. This may have been due to their discovery of its antimicrobial properties.
Copper is sought after for its malleable and ductile properties. It also conducts heat and electricity very well. This would explain why it is most commonly used in electronics and wiring.
Natural Aging of Copper
Copper, like most other metals, oxidises. The resulting colour is usually a pale or dull green. This is the reason that the statue of liberty is green in colour. The layer of oxidation alone is estimated to be around 0.127mm thick and it has added an additional 80t of weight to the statue, this oxidation layer occurred gradually over a period of 34 years (Complete by 1920).
For more information on the aging and patina of copper and other metals see our Architectural & Bespoke Metal Finishes Page.
Copper’s antimicrobial properties have been known for many years which is one of the main reasons it is used for water pipes and plumbing.
In recent times, copper has become very popular in the medical field and many hospitals have begun installing copper to frequently touched surfaces.
This has shown a dramatic reduction in hospital acquired infections which kill tens of thousands of patients every year.
Copper creates its own barrier which can kill up to 99.9% of bacteria.
Unlike traditional surfaces of stainless steel and plastic which we rely on being cleaned and washed by cleaning staff, copper works 24 hours a day 7 days a week actively killing these cells.
In 2013, researchers led by Salgado tested copper surfaces in intensive care units in three hospitals. The scientists found that 12.3 percent of patients developed antibiotic-resistant infections (MRSA, methicillin-resistant Staphylococcus aureus, and VRE, vancomycin-resistant Enterococcus) in traditional rooms.
In the copper-modified rooms, only 7.1 percent of patients contracted one of these potentially devastating infections.
“We know that if you put copper in a patient’s room, you’re going to decrease the microbial burden,” Salgado told Live Science. “I think that’s something that has been shown time and time again. Our study was the first to demonstrate that there could be a clinical benefit to this.”
Nothing else about the ICU conditions were changed apart from the copper; nurses and doctors still washed their hands and routine cleaning went on as usual. The research was published after their findings in 2013 in the journal Infection Control and Hospital Epidemiology.
More information can be found on our Antimicrobial Copper Page.
Since prehistoric times copper has been an essential metal, both in its pure state or used in the creation of copper alloys such as brass and bronze.
Bronze was so popular that one of the major “ages” or stage of human history was named after this copper alloy, the Bronze Age.
Copper and its alloys have been very important for many civilisations including, the Ancient Egyptions, the Romans, the Chinese and modern civilisation.
There are many references and artefacts that can be researched, some dating back to 8,000 B.C.
What is Mild Steel?
Mild steel is also known as carbon steel or plain carbon steel, due to its composition from iron and carbon; plus lesser elements which are too minimal to affect the properties of the alloy.
The term ‘mild steel’ refers to steels that have a low carbon content (max of 0.3%), but which also have material properties which are highly suitable for fabrication. Properties include its good strength, its suitability to be bent and formed into a wide variety of shapes and its ability to be welded. This makes mild steel suitable for many uses.
Properties of Mild Steel
Having a low carbon content of 0.05% to 0.3% means it quite rigid without being brittle.
The low carbon content makes it soft like iron, so whilst it is tough and durable it is also malleable and ductile which is ideal for forming. It is also less expensive.
Mild steels downfall is that it rusts of not properly protected.
A higher carbon content would make it stronger but also harder, less flexible and more difficult to weld because it has a lower melting point.
Higher carbon steel is also more expensive.
Fabrication of Mild Steel
The workability of Mild Steel makes it very favourable to work with and suitable to most applications, provided it is protected from the elements well.
It is less brittle than the higher carbon steels, enabling it to flex so we can bend, fold, punch and laser cut it into shapes and forms without it breaking. It also has higher heat resistance making it easier to weld.
Mild steel easily rusts and therefore must be protected, please scroll below for Protection of Mild Steel.
Uses of Mild Steel
Because mild steel is such a highly versatile material it is used to produce many everyday objects as well as commercial goods and projects, especially if a large amount of metal is needed.
Mild Steel Properties
Mild Steel is one of the most common of all metals and one of the least expensive steels used. It is to be found in almost every metal product.
Mild Steel is weldable, very durable (although it rusts) and it is relatively hard and is easily annealed.
Having less than 2% carbon, it will magnetize well and being relatively inexpensive, can be used in most projects requiring a lot of steel. However when it comes to load bearing, its structural strength is not usually sufficient to be used in structural beams and girders.
Most everyday items made of steel have some Mild Steel content. Anything from cookware through to motor car chassis.
Because of its poor resistance to corrosion it must be protected by painting or otherwise sealed to prevent it from rusting. At worst a coat of oil or grease will help seal it from exposure, and help prevent rusting.
Being a softer metal it is easily welded. Its inherent properties allow electrical current to flow easily through it without upsetting its structural integrity. This is in contrast to other high carbon steels like stainless steel which require specialized welding techniques.
This mild variant of harder steel is thus far less brittle and can therefore give and flex in its application where a harder more brittle material would simply crack and break.
Protection of Mild Steel
How Do We Stop Steel From Corroding?
Below is a list of methods used to protect Mild Steel
Passive Barrier Protection
Passive barrier protection works by coating the steel with a protective coating system that forms a tight barrier to prevent exposure to oxygen, water and salt (ions). The lower the permeability of the coating system to water, the better the protection provided. Two-pack epoxy coatings and chlorinated rubbers applied at sufficiently high film builds offer the most successful corrosion protection through passive barrier protection.
Active corrosion protection occurs when a primer containing a reactive chemical compound is applied directly to the steel. The reactive compound disrupts the normal formation of anodes on the surface of the steel in some way. For example, inorganic zinc inhibitive pigments, such as zinc phosphate, offer active anti-corrosive protection to the steel substrate (Zinc phosphate (Zn3(PO4)2) and is only slightly soluble in water). It hydrolyses in water to produce zinc ions (Zn2+) and phosphate ions (PO43-). The phosphate ions act as anodic inhibitors by phosphating the steel and rendering it passive. The zinc ions act as cathodic inhibitors.
Sacrificial Protection (Cathodic Protection or Galvanic Protection)
The above-mentioned reaction between dissimilar metals can be used to protect steel against corrosion. The most widely used metal for the protection of steel is zinc. Zinc metal in direct contact with the steel substrate offers protection through the preferential oxidation of zinc metal.
Zinc is a great choice in protecting steel, as not only does it corrode in preference to the steel, the rate of corrosion is generally slower. This rate, however, is accelerated in the presence of ions such as chlorides in coastal locations.
Electrophoretic deposition is a process in which electrically charged particles are deposited out of a water suspension to coat a conductive part.
The process is more commonly known as electrocoating or E-coating.
The idea of electrically discharging polymers to coat an object was first considered in the 1930’s. Most of the basic research was conducted in Europe in the 1960’s. North American companies began electrocoating in the late 1960’s and the process has been widely used for coating metal parts ranging from simple stampings to complex auto bodies.
The process requires a coating tank in which to immerse the part, as well as temperature control, filtering and circulation equipment.
Electrocoating systems are known as anodic or cathodic depending upon whether the part is the anode or cathode in the electrochemical process.
Cathodic systems are more common since they require less surface preparation and provide better corrosion resistance.
Electrocoating requires that the coating binder, pigment and additives be given an electrical charge. These charged materials, under the influence of an electric field, migrate through water to the part surface.
Once at the part, the charged materials give up their charge due to neutralization by electrochemically generated OH- ions (cathodic process). Upon giving up their charge, the coating materials drop out of the water suspension and coalesce as a coating on the part surfaces.
Electrocoat thickness typically ranges from 10 to 30 micrometres (0.4 to 1.2 mils). Automotive parts that are electrocoated usually receive a zinc or iron phosphate treatment prior to deposition. This treatment enhances the application of the E-coat.
Various types of metallic coatings can be applied to ferrous and non-ferrous substrates to inhibit corrosion and/or provide a decorative finish. The choice of a particular coating material is dependent upon the severity of the corrosive environment, whether the part is subject to wear and abrasion, and the degree of visibility of the part in service.
Four common methods for applying metallic coatings are:
Electroplating: The coating is deposited onto the substrate metal by applying an electrical potential between the substrate metal (cathode) and a suitable anode in the presence of an electrolyte. The electrolyte usually consists of a water solution containing salt of the metal to be deposited and various other additions that contribute to the plating process.
Mechanical plating: Finely divided metal powder is cold welded to the substrate by tumbling the part, metal powder and a suitable media such as glass beads, in an aqueous solution containing additional agents. Mechanical plating is commonly used to apply zinc or cadmium to small parts such as fasteners.
Electrolyses: In this non-electric plating system, a coating metal, such as cobalt or nickel, is deposited on a substrate via a chemical reaction in the presence of a catalyst.
Hot dipping: A coating metal is deposited on a substrate by immersing the substrate in a molten bath of the coating metal. Many underbody structural components are manufactured from sheet steel with a metallic coating. The steel mills supply hot or cold rolled sheet in coil form with metallic coatings applied by either electroplating or hot dipping. The most commonly supplied coatings include zinc, zinc-iron, zinc-nickel, aluminium, aluminium-zinc, tin and lead-tin.
The application of an organic coating, such as paint, is a cost effective corrosion protection method. Organic coatings act as a barrier to a corrosive solution or electrolyte. They prevent, or retard, the transfer of electrochemical charge from the corrosive solution to the metal underneath the organic coating.
The coating thickness of the auto-deposition film is time and temperature dependent. Initially, the deposition process is quite rapid, but slows down as the film begins to build or mature. As long as the part being coated is in the bath, the process will continue; however, the rate of deposition will decline.
Typically, film thicknesses are controlled from 15 to 25 micrometres (0.6 to 0.8 mils). Auto-deposition will coat any metal the liquid touches. Parts that are tubular in shape, assembled parts or parts that have intricate designs can also be coated by this process. Auto-deposition does not require a phosphate stage and the coating is cured at a relatively low temperature.
In the powder coating process, a dry powder is applied to a clean surface.
After application, the coated object is heated, fusing the powder into a smooth, continuous film.
Powders are available in a wide range of chemical types, coating properties and colours. The most widely used types include acrylic, vinyl, epoxy, nylon, polyester and urethane.
Modern application techniques for applying powders fall into four basic categories: fluidized bed process, electrostatic bed process, electrostatic spray process and plasma spray process.
The electrostatic spray process is the most commonly used method of applying powders. In this process, the electrically conductive and grounded object is sprayed with charged, non-conducting powder particles. The charged particles are attracted to the substrate and cling to it. Oven heat then fuses the particles into a smooth continuous film. Coating thicknesses in the range of 25 to 125 micrometres (1 to 5 mils) is obtained. Controlling a low film thickness is difficult. A booth and collection system can be used to collect overspray for re-use.
Rust is another name for iron oxide, which occurs when iron or an alloy that contains iron, like steel, is exposed to oxygen and moisture for a long period of time. Over time, the oxygen combines with the metal at an atomic level, forming a new compound called an oxide and weakening the bonds of the metal itself.
Although some people refer to rust generally as “oxidation,” that term is much more general; although rust forms when iron undergoes oxidation, not all oxidation forms rust. Only iron or alloys that contain iron can rust, but other metals can corrode in similar ways.
The main catalyst for the rusting process is water. Iron or steel structures might appear to be solid, but water molecules can penetrate the microscopic pits and cracks in any exposed metal.
The hydrogen atoms present in water molecules can combine with other elements to form acids, which will eventually cause more metal to be exposed. If chloride ions are present, as is the case with saltwater, the corrosion is likely to occur more quickly.
Meanwhile, the oxygen atoms combine with metallic atoms to form the destructive oxide compound. As the atoms combine, they weaken the metal, making the structure brittle and crumbly.
Oxidation of iron
When impure (cast) iron is in contact with water, oxygen, other strong oxidants, or acids, it rusts. If salt is present, for example in seawater or salt spray, the iron tends to rust more quickly, as a result of electrochemical reactions.
Iron metal is relatively unaffected by pure water or by dry oxygen. As with other metals, like aluminium, a tightly adhering oxide coating, a passivation layer, protects the bulk iron from further oxidation. The conversion of the passivating ferrous oxide layer to rust results from the combined action of two agents, usually oxygen and water.
Other degrading solutions are sulphur dioxide in water and carbon dioxide in water. Under these corrosive conditions, iron hydroxide species are formed. Unlike ferrous oxides, the hydroxides do not adhere to the bulk metal.
As they form and flake off from the surface, fresh iron is exposed, and the corrosion process continues until either all of the iron is consumed or all of the oxygen, water, carbon dioxide, or sulphur dioxide in the system are removed or consumed.
When iron rusts, the oxides take up more volume than the original metal; this expansion can generate enormous forces, damaging structures made with iron. See Economic effect for more details.
Aluminium is a chemical element in the boron group with a symbol of Al and an atomic number of 13. It is a silvery white, soft, nonmagnetic, ductile metal. Aluminium is the 3rd most abundant metal in earth’s crust and the most abundant element after oxygen and silicon. Aluminium makes up about 8% of the earth’s crust.
Aluminium in its natural state is very chemically reactive and so it is rare to find in its pure state; instead it is usually found combined in over 270 different minerals, the most common ore of aluminium is bauxite.
Aluminium is well known for its low density and its corrosion resistance ability’s, for this reason aluminium and its alloys are vital to the aerospace industries, transportation industries and building structures.
Aluminium can be easily cast or formed while still retaining good strength, common items made from aluminium are, cans, foils, utencils, window frames and sports cars
Chemical Properties of Aluminium
The corrosion resistance of aluminium is generally very good due to the thin surface layer of aluminium oxide that forms when the bare metal is exposed to air. This layer is protective, the process of which is called passivation. Corrosion resistance is greatly diminished when submerged in salt water, especially in the presence of dissimilar metals.
When subjected to highly acidic solutions & high alocoli solutions, aluminium reacts with the water to form hydrogen gas. Aluminium, in finely powdered form, still retains its silvery reflective appearance, for this reason it is used in metallic and silver paints.
Aluminium can be polished to a very high reflectivity, It can also be aged or patinas can be applied to get a large variety of colours.
For more information on patinas and aging see our Architectural & Bespoke Metal Finishes Page.
Grades of Aluminium
Below are some of the more common grades of aluminium.
|Alloy 1100||Excellent||Excellent||Good||Excellent||No||Low||Metal Spinning|
|Alloy 2011||Good||Poor||Excellent||Poor||Yes||High||General Machining|
|Alloy 2024||Good||Poor||Fair||Poor||Yes||High||Aerospace Application|
|Alloy 3003||Excellent||Excellent||Good||Good||No||Medium||Chemical Equipment|
|Alloy 5052||Good||Good||Fair||Excellent||No||Medium||Marine Applications|
|Alloy 6061||Good||Good||Good||Excellent||Yes||Medium||Structural Applications|
|Alloy 6063||Good||Good||Fair||Good||Yes||Medium||Architectural Applications|
|Alloy 7075||Poor||Poor||Fair||Average||Yes||High||Aerospace Applications|
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