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January - February 2014 : Are black magnetic particles coloured or not?

Written by Laurence
Monday, 13 January 2014 14:16

A rather peculiar question sent to people involved in Magnetic Particle Testing!

And yet in the ISO 9934-2:2002 standard, we find:

Paragraph 5.2
“Magnetic inks shall consist of finely divided coloured or fluorescent magnetic particles...”

Paragraph 5.3
“Powders for the dry technique shall consist of finely divided coloured and/or fluorescent magnetic particles.”

It occurs that, in the Magnetic Particle Testing method, there are magnetic inks and magnetic powders that contain black magnetic particles. Some people, purists, to say the least, say that black…is not a colour.

Georges Clemenceau, the French “Tiger” of 1WW, who made the military obey the civilian power, insisted on the fact that the body of the renowned impressionist painter Claude Monet should not be covered with a black shroud, explaining that it was not appropriate: "No black for Monet! Black is not a colour! "

Is this that simple?

Black is the visual appearance of objects that do not emit or reflect any part of the visible light spectrum. Even if black is sometimes said to be achromatic or tint-free, it may be considered in practice, as a colour, as in the expressions "black cat" or "black paint".

Indeed, if one considers the subtractive colour process, black comes as due to a blend of pigments that absorb a visible wavelength, combined to absorb all of them, thus it is a colour, got from a mix. On the other hand, if considering the additive colour process (superposition of monochromatic light beams), black is the absence of any colour. In the RGB (Red-Green-Blue) standard colorimetric space, its coordinates are (0, 0, 0).

Thus, black is exactly the reverse of white, as white comprises all the wavelengths of the visible spectrum. When combining the three primary colours in equal proportions in the additive colour process, one goes from black to white, including all the gray shades. In common language, white and black are called "non-colours".

In order to avoid any talking on this topic that deals both with physics and semantics, would it not be easier to use the term "nonfluorescent particles" of the ASTM E1444/E1444M – 12 standard?

Why complicate matters when they can be simple? [This is the reverse of the adage often used in France: « Pourquoi faire simple quand on peut faire compliqué ? ») (Editor’s note: Why make it simple when it can be complex?) when dealing with legal texts.]

Normative references

ISO 9934-2:2002, Non-destructive testing -- Magnetic particle testing -- Part 2: Detection media, International Organization for Standardization, Geneva, Switzerland, 2002.

ASTM E1444/E1444M - 12 Standard Practice for Magnetic Particle Testing, ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA, 19428-2959, USA, 2012.


Last Updated ( Monday, 27 January 2014 20:16 )