Sunday, 18 September 2011

How Neel or Ultramarine Blue Whitens Fabrics

What is Neel

Neel is used very commonly in washing of the white clothes. It is interesting to know the chemical and other facts about this chemical. 

Neel is a chemical called Ultramarine Blue. It is a blue pigment consisting primarily of a double silicate of aluminium and sodium with some sulfides or sulfates. It is the most complex pigment found in nature. It is found in the natural state in the mineral of Lapis Lazuli. Now it is also produced artificially. 

The name Ultramarine essentially means "Beyond the Sea", because it was imported from Asia by sea. 

How it Effects Fabrics

White fabrics become yellow or grey after some washing. Since blue and yellow are complementary colors in the subtractive color model of color perception, adding a trace of blue color to the slightly off-white color of these fabrics makes them appear whiter. Ultramarine has a red undertone which means it reflects at both the blue and red end of the spectrum but absorbs only the unwanted yellow component. Most other blues are having green undertone. In addition to absorbing the yellow component they also absorb the red and therefore cannot give such a balanced correction as ultramarine does. 

Ultramarine is a pigment and not a dye. It is insoluble in water and keep itself only by agitation. Upon washing some of the ultramarine particles become trapped in the fabric which gives it blue undertone. Next washing these particles come out and new particles take their place. Thus it is an auto correcting Mechanism. 

If too much of the ultramarine is added, it will give a pale blueness to the fabric, instead of brilliant whiteness. If a rapid correction is required, rinsing with some lime or vinegar will easily remove the excess blue color.  

Particle size is also important. If particle size is less than 1 micron, then in the next washing the particles do not get washed out and blueness keeps on increasing. Ideally a size of 2-3 micron is recommended. 

It should be remembered that Ultramarine improves the whiteness of the fabric, but not the brightness. In fact as it subtracts the absorption of yellow light, it reduces the brightness making the fabric appear dull. 

Brightness can be increased by using some optical brighting agent.

Sources : Wikipedia, 1, 2

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