The blotter spot test has been discussed numerous times in the pages of Machinery Lubrication magazine. It not only is one of the oldest oil analysis tests (mid-19th century) but endures as one of the most effective at detecting and even quantifying certain lubricant abnormalities.

However, the blotter spot test is not commonly known as a test for detecting and examining particles in oil such as wear debris and dirt.

As a practical matter, its ability to reveal normal and even slightly abnormal amounts of solid particles is limited, especially without the aid of a microscope. This generally is true with other applications of blotter spot testing.

In other words, the lack of a visible structure (rings, starbursts, pasty center, etc.) is an indication of the absence of the target condition. Because of this, the blotter spot test is less likely to produce a false negative compared to other more advanced analytical methods.

While each method has its own unique interferences and lower sensitivity limits, the ability of blotter spot testing to provide a reliable alert to abnormal particle concentrations is undisputable.

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