Dispersion Staining without Specialised Objectives

Robert Pavlis, Girard, Kansas USA

Jim Benko, Zeeland, Michigan USA

The May 2008 issue of Micscape one of the authors of this article, Robert Pavlis, described the principle of dispersion staining, an important analytical technique that can be used to identify many materials, though the technique is most commonly used for asbestos. The article contained two images that showed a special dispersion staining objective that is commonly used for this technique. Unfortunately these objectives are rather expensive. We describe here a much less expensive alternative!

The other author of this article, Jim Benko, pointed out that there is a way to utilise dispersion staining without purchasing a special objective. The technique that will be described is one that one would not want to use with an expensive high quality objective. However, it is possible today to purchase standard microscope objectives, generally made in China or India, for a few pounds or dollars. The dispersion staining objectives have a central occulting disk mounted directly behind the last lens element of the objective. There is a simple and inexpensive alternative!

The alternative is to place a small dot directly on the rear element of an inexpensive objective. The best material to make the dot is either India ink or, probably better, an oil based flat black paint or enamel. An excellent way to make circular dots like this is to use a small diameter circular wooden rod. Match sticks or round tooth picks can work very well. The dot needs to be at the exact centre of the objective, and it needs to be the correct size. Should one err in placing the dot, it can be "erased" using xylene. (Be careful to use xylene very sparingly so that it does not damage lens cements.)

Certain paints and enamels (such as epoxy and polyurethane ones) form cross links on curing. It is best to avoid these, because it can be difficult to remove them once they are fully cured.

Many microscopists tend to have extra objectives lying around. This is an interesting way to provide an interesting use for them.

All comments to the authors via Robert Pavlis are welcomed.

 

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Published in the June 2008 edition of Micscape Magazine.

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