Coverslip and microscope slide materials

Are all microscope slides the same? We field this question quite often and would like to share some under-the-microscope details about laboratory coverslips and slides. In short, not all glass laboratory objects are created equal. Buying in bulk will save on price, but generally, you compromise on quality. For labs and universities that need low-budget lab supplies, you likely see there is variability in slides when purchased in bulk packs; edges may be sharp, chips and breaks occur easily and slides may have particles or residue from manufacturing. For Esco’s lab supplies, even though these are consumable pieces of glass, we are sure to inspect edges and cleanliness before shipping.

Your choice of slide material is likely dependent on what function you are trying to perform. Let's look at three types of microscope slide material: borosilicate glass, quartz, fused silica, and some of their properties.

Borosilicate glass is a float glass which refers to its fabrication method. In its molten form, the glass is floated over a large metal surface (usually tin) and then cooled as a sheet. Borosilicate glass has high transparency in visible and near IR & UV range of wavelengths, as well as, high optical clarity.

Quartz is an example of crystalline silica-based material. Fused quartz is made by the melting of highly pure, crushed natural quartz. Quartz features a much lower OH content than fused silica. Due to metallic impurities in the crushed precursor material, it does not transmit well in the ultraviolet spectrum. Quartz is known for its thermal stability and high chemical resistance.

Fused Silica and quartz are similar, but the key differentiator is that fused silica is composed of non-crystalline silica glass. It is made by melting extremely pure silica through a flame hydrolysis process where it oxidizes and forms an amorphous (crystal-free) structure. Its non-crystalline structure gives fused silica a very high transmission in the UV spectrum compared to that of quartz. When exposed to high-intensity radiation such as UV light, many materials will absorb the energy and re-emit it, thereby fluorescing. This effect introduces unwanted noise and can interfere with microscopic observations. Fused silica is an excellent option and provides extremely low, and in many cases, no fluorescence in the presence of such radiation.

When performing any microscopic work, you want to ensure your slide or coverslip material will be optically clear and free of surface defects. Be sure to find the right optical material that suits your application. Compare specifications and remember items bought in bulk by your purchasing department may look good on the bottom line, but in person can be sub-par. A quality product from a trusted supplier will ensure the best results under the microscope.