The main disadvantage to spark testing is its inability to identify a material positively; if positive identification is required, chemical analysis must be used.
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Spark testing most often is used in tool rooms , machine shops , heat treating shops, and foundries. A bench grinder is usually used to create the sparks, but sometimes this is not convenient, so a portable grinder is used. The wheel should be coarse and hard, therefore aluminium oxide or carborundum often are employed.
The test area should be in an area where there is no bright light shining directly into the observer's eyes. Moreover, the grinding wheel and surrounding area should be dark so that the sparks can be observed clearly.
The test sample is then touched lightly to the grinding wheel to produce the sparks. The important spark characteristics are color, volume, nature of the spark, and length. Note that the length is dependent on the amount of pressure applied to the grinding wheel, so this can be a poor comparison tool if the pressure is not exactly the same for the samples.
Also, the grinding wheel must be dressed frequently to remove metallic build-up. Another less common method for creating sparks is heating up the sample to red heat and then applying compressed air to the sample. The compressed air supplies enough oxygen to ignite the sample and give off sparks.
This method is more accurate than using a grinder because it will always give off sparks of the same length for the same sample. The compressed air applies in essence the same "pressure" each time. This makes observations of the spark length a much more reliable characteristic for comparison. Automated spark testing has been developed to remove the reliance upon operator skill and experience, thereby increasing reliability. The system relies upon spectroscopy , spectrometry , and other methods to "observe" the spark pattern.
It has been found that this system can determine the difference between two materials that give off sparks that are indistinguishable to the human eye. In ,  Max Bermann, an engineer in Budapest , was the first to discover that spark testing can be used reliably to classify ferrous material. He originally claimed to be able to distinguish different types of ferrous materials based on percent carbon and principal alloying elements. Moreover, he claimed to achieve an accuracy of 0.
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