Canada balsam. Light micrograph of canada balsam drying on a microscope slide and forming a net- like, or reticular, pattern. Canada balsam, which comes from the balsam fir (Abies balsamea), is a resin dissolved in essential oils. When dry it is transparent and has a refractive index very close to that of glass. It is used to mount and preserve samples on microscope slides, and to repair scratches in glass.