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Rust Spots

One of the most common identifying age signs of antique porcelain is rust spots. These are spots caused by the residue of iron oxide surfacing. Meaning, these minute remains of iron tend to appear on the surface of porcelain as time passes.

With glaze applied over the clay body, the residue causes dark spots that appear on the surface.

The color of genuine rust spots varies from yellowish-brown to brown. Plus, they are often small.

Modern potters, who try to turn new porcelain into antique pieces, are continuously finding ways to add these rust spots. However, most of them fail since the spots they make are either orange or reddish instead of brown or blackish.

Many say that they even try using computers to determine the exact color or shade of genuine spots. Unfortunately, computers cannot perfectly imitate the right shade or darkness.

How Rust Spots Are Formed

Rust spots usually appear after the heating or cooking process in kilns. When the process is done, rust spots reach the surface and try to escape into the air.

However, the glaze is applied over the body of real antique porcelains, so residues are cooked or trapped underneath. As a result, dark spots appear.

Some porcelain pieces don’t necessarily have brown or dark spots. Others have yellowish to brown colors that come in distinct shapes.

Imitation spots are often big and without shape. Sometimes, its color appears too red or too black. Or, the deep dark colors look somewhat off.

Against a green background, rust spots usually appear in brown splashes. These may be caused by different chemical reactions depending on the contents of the clay and glaze. Thus, there is no perfect or specific color for these spots.

Rust Spots as an Authenticating Criteria

Today’s experts see rust spots as a significant sign of an authentic antique rather than an imperfection. Hundreds of years ago, Yuan era porcelain was rich in iron. Some even used this component as a design itself.

Some potters would use the accumulation of iron oxide from cobalt blue as an effect for their final piece’s design. For example, they would use a cobalt blue stone to shade an entire surface of a bowl. This resulted in rust spots that appeared as tiny dark specks all over the surface.

However, these pieces were only given as gifts to highly deemed guests.

Different shades of cobalt blue were used throughout the Tang, Yuan, and Ming dynasties. At a certain period, the cobalt ores became rare, so they had to be imported all the way from Persia.

These Persian cobalt blue shades often had higher iron oxide content.

Antique pieces made from ores with higher iron oxide had higher possibilities of having rust spots. Compared to other antiques of other eras, Ming and Yuan pieces had more rust spots. Those who authenticate antiques can use this characteristic to determine which period it was made.

Rust spots were often seen at the base or rim of the antique, which was usually white. Most Ming pieces had enough time for these spots to surface. Since clay is a natural substance with a high chance of impurity, iron oxide surfaces from the clay.

Even multi-colored Qing pieces had rust spots. So, a few potters took advantage of high iron-red or blue to use in their masterpiece. A few used them in their dragon designs to create an embossed effect.

Though there were only a few Qing antiques with rust spots, they were generally present.

Can Rust Spots be Imitated?

Though rust spots can be imitated, it is not common since it’s difficult to imitate. Sometimes, pieces can have just one spot, while others can have a cloud or group of spots. This is why faking these can be a challenge.

During the 18th and 19th centuries, fake antiques were dated with their year of manufacturing. They weren’t considered fakes since they were sold as imitations of the 14th or 15th-century pieces.

They crafted these imitations as pieces to showcase the art of the past, rather than something claiming to be it.

Eventually, people have grown interested in real antique pieces, and these became high in demand. As a result, fake pieces claiming to be authentic started becoming rampant. Although the imitations are beautiful, these are simply modern copies.

Techniques and technology for both the authenticator and the fakers have improved over the past years. Today, rust spots are added, and computer-generated techniques are used to copy real antiques. But in the eyes of a real porcelain master, these cannot be missed.

The natural effect of how the rust spots formed vary according to time and climate. Also, clay and the level of impurities in a piece affect the formation of rust spots.

However, no one can use these factors to determine if rust spots, or how many of these, would surface.