Canada balsam
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Canada balsam, also called canada turpentine or balsam of fir, is a turpentine which is made from the resin of the balsam fir.
It is the fir's resin, dissolved in essential oils, and is a viscous, sticky, colourless (sometimes yellowish) liquid, that turns to a transparent yellowish mass when the essential oils have been allowed to evaporate.
Due to its high optical quality, its refraction index very close to that of glass, and its purity it is mainly used in optics as an invisible-when-dry glue for glass, e. g.
- in biology to conserve microscopic samples (The sample is sandwiched between the microscope slide (a glass plate) and the cover plate (a small thin glass plate) and canada balsam is used to glue the arrangement together and enclose the sample to conserve it)
- in optical technology to glue together optical elements such as two prisms to form a beam splitter, or two lenses
- to fix scratches in glass (e.g. car glass) as invisibly as possible