Oxidation / Corrosion vs. Wear With A Ficus On Antique Rugs
Corrosion, oxidation and wear are terms that you might hear when buying an antique rug. These are both a type of change that occur in rugs over time, but they are very different. The presence of corrosion / oxidation gives the rug an aged look and patina which lets you know that it is an authentic antique. Let’s explore how oxidation / corrosion and wear happen so that you will understand them as you evaluate rugs for your collection.
For starters – what is Oxidation?
Oxidation is a chemical process that involves the loss of electrons by a substance. It occurs when a chemical species, often referred to as a reducing agent or reductant, donates electrons to another chemical species, called an oxidizing agent or oxidant. This transfer of electrons results in the increase in the oxidation state of the oxidized substance and a corresponding decrease in the oxidation state of the reduced substance.
Key points about oxidation include:
- Electron Transfer: Oxidation is essentially the transfer of electrons from one atom or molecule to another. The substance that loses electrons is oxidized, and the substance that gains those electrons is reduced. This is why oxidation and reduction are often referred to as redox reactions.
- Oxidation State: The oxidation state, or oxidation number, of an element or compound reflects its electron distribution. When an element is oxidized, its oxidation state becomes more positive, indicating that it has lost electrons. Conversely, when it is reduced, its oxidation state becomes more negative, indicating that it has gained electrons.
- Oxidizing Agents: Oxidizing agents are substances that readily accept electrons and, in the process, cause other substances to undergo oxidation. Common examples of oxidizing agents include oxygen (O2), hydrogen peroxide (H2O2), and various metal ions.
- Oxidation Reactions: Oxidation reactions are prevalent in various chemical and biological processes. For example, the rusting of iron is an oxidation reaction where iron atoms lose electrons to oxygen molecules, forming iron oxide (rust). In biological systems, cellular respiration involves the oxidation of glucose to produce energy.
- Redox Potential: The tendency of a substance to undergo oxidation or reduction is quantified by its redox potential or electrode potential. Substances with higher redox potentials are more likely to act as oxidizing agents.
- Importance: Oxidation-reduction reactions are fundamental in many natural processes, including combustion, corrosion, metabolism, and photosynthesis. They also play a critical role in the functioning of batteries, fuel cells, and various chemical industries.
Corrosion Vs. Wear
Oxidation is a chemical process characterized by the loss of electrons, resulting in an increase in the oxidation state of a substance. It is a fundamental concept in chemistry with wide-ranging implications in both natural and industrial processes.
What is wear?
Wear refers to the gradual removal or damage of material from a solid surface as a result of mechanical action or friction between two surfaces in contact. It is a common phenomenon in everyday life and engineering and can have a significant impact on the durability and performance of various materials and mechanical components.
There are several types of wear mechanisms, including:
- Abrasive Wear: This occurs when hard particles or abrasive materials come into contact with a softer surface, leading to the removal of material through abrasive action. An example is the wear of cutting tools due to contact with workpiece material.
- Adhesive Wear: Adhesive wear, also known as galling or scuffing, happens when two surfaces adhere to each other and then separate, often causing small amounts of material to be transferred from one surface to the other. It is common in metal-to-metal contact situations, such as in bearings and gears.
- Erosive Wear: Erosive wear occurs when solid particles or abrasive fluids, like slurries, impact a surface at high velocities, causing material to be removed. This is often encountered in industries like mining, where materials are transported with abrasive particles.
- Fatigue Wear: Fatigue wear is the result of cyclic loading on a material, leading to the initiation and propagation of cracks and ultimately material failure. It is common in components subjected to repeated stress, such as axles and springs.
- Corrosive Wear: This type of wear occurs in the presence of corrosive substances, such as chemicals or moisture, which can chemically attack and weaken the material while mechanical action further removes material. It often affects materials like metals and can be observed in pipelines and containers handling corrosive fluids.
- Fretting Wear: Fretting wear happens at the interface between two contacting surfaces that undergo slight relative motion due to vibration or oscillation. It can result in surface damage and material loss, particularly in bolted joints and bearings.
Understanding and mitigating wear is essential in various fields, including mechanical engineering, materials science, and tribology (the study of friction, lubrication, and wear). Engineers and scientists employ various techniques to reduce wear, such as using lubricants, employing wear-resistant materials, and designing components with improved geometry and surface treatments to minimize friction and abrasion. The study of wear and its control is crucial for extending the lifespan and efficiency of mechanical systems and machinery.
Oxidation, Corrosion and Metals in the Dyeing Process
Corrosion and oxidation are pretty synonymous terms that you typically associate with metal, not rugs. When metal corrodes / oxidizes, it reacts with oxygen in the air. If the metal is iron, then it will result in rust. When copper corrodes / oxidizes it turns green, like statue of liberty in NYC, and breaks down with time. These are all signs of the passage of time and indications that an item is old.
The Statue of Liberty is colored green due to oxidation.
What people sometimes don’t realize is that when we talk about oxidation or corrosion in rugs, we are still talking metal. Some natural carpet dyes have metals in them and are comprised of materials such as iron, copper, chromium, tin and aluminum to allow the color to adhere to the fiber. Metals and metallic salts make the dyestuff more permanent and lightfast. This means that it will not fade over time, and the colors will, for the most part, stay truer. This is what allows many rugs, carpets and textiles to remain nearly as bright and vibrant as when they were created, even after several hundred years of use.
If the rug is an antique, iron and copper were used, as they were the most common metals used in the color dyeing process. Iron is usually in the form of ferrous sulfate. Copper is usually soaked in vinegar to extract cupric acetate that is then used to dye the cloth. Chemically, these metals act as a bridge between the fiber and the color molecule, allowing it to create a tighter bond.
Antique rug dyes were made with natural materials and metallic salts.
How Oxidation and Corrosion Changes Rugs
The dye colors created with metallic salts are responsible for the beautifully harmonious tones that we associate with natural dyes, but they have a “dark side”. Over time, these metals that are within the dyes themselves will begin to oxidize and corrode. When they do, it can break down the wool or silk fibers with them. As this occurs, the rug pile will become brittle and flake off a tiny little bit at a time. When you run your hand over these oxidized areas, the corroded sections will feel a bit rougher and have a lower pile height than the areas around it that didn’t use metals in the dye. This creates a high / low embossed look and feel and will be especially present in the darker colored areas of the design.
Notice how the dye in two of the animal figures has begun to corrode on this rug.
Corrosion might occur over the whole rug, but it is seldom evenly worn as different dyes have different concentrations of the metallic elements. That is why you might find that the lower pile corroded areas are only noticeable in certain colors. It is more common in darker colors like brown and black, because those colors require more iron to create. This uneven pile is what gives the carpet that high-low appearance. You will sometimes see white warp and weft threads of the rug’s foundation peaking through in areas of low pile.
The dye in this rug has begun to corrode, exposing the warp.
Recognizing Actual Wear – Not Corrosion
Wear in rugs can look similar to corrosion in some ways. That said, there are a few things that distinguish it from oxidation. A rug wears simply as a result of people walking on it over time. Wear reflects the utilitarian purpose of the rug.
As people walk on the rug over long periods of time, little pieces of the wool break off. Eventually, just as with corrosion, the white warp will begin to show through. This might appear as little white flecks, singular white knots, or it might be more pronounced, and you can see white warp threads on the front (pile side) of the rug. On many rugs with heavy wear on the pile, the fringe or the ends will tend to be ragged or very short, too.
Differences Between Corrosion and Wear
Corrosion will usually differ according to different color areas. Wear is more uniform across the surface where people were walking and will not show more or less wear based on color. Sometimes, a carpet might wear all over, but it might also occur where the rug was walked on the most. For instance, there might be a visible area down or across a section of the rug where you can see evidence of foot traffic.
Wear, not corrosion, shown across a Sultanabad rug.
Now that you understand the difference between corrosion and wear, you will be able to recognize it in antique rugs. Corrosion and wear are not always a bad thing in antique rugs. They give rugs a unique shabby chic texture and character and let you know that it is an authentic antique.
Feel free to take a look around at the fine antiques in our collection and see if you can spot the hallmarks of a real antique rug through corrosion and wear.
This rug blog about the differences between corrosion and wear was published by Nazmiyal Antique Rugs.
