You have a beginner microscope and you’re thinking, what’s next? Time to magnify your subjects! But before magnifying them, you must first know how to prepare your slides. Standard slides are usually made of plastic or glass. For general purposes, glass slides that are 1 to 1.2 mm thick are used. When working with high power beginning microscope objectives and condensers, the slide thickness should be lessened to 0.8 to 1 mm. Always order more than what you are expecting to use. The slides are usually packaged in increments of 72.

Two different types of microscope slides are generally in use: the common flat glass slide and the depression or well slide. These slides are rectangular and measure roughly 1 x 3 inches (25 x 75 mm). To hold a drop of liquid, depression slides have an indentation in the center. They cost noticeably more than the flat variety, but they are usually used without a cover slip.

It is important first to have all necessary materials on hand when preparing microscope slides for to be used for your beginning microscope. These materials include slides, cover slips, pipets or droppers and any chemicals or stains you are planning to use. A very thin square piece of glass (or plastic), called a cover slip or cover glass, is placed over the water drop. Due to surface tension, the water drop alone will be predisposed to sit in a thick dome. With the cover slip on top, the drop is flattened, allowing you to focus with high power very near to the specimen. It also confines the specimen to a single plane and decreases the amount of focusing needed with your beginning microscope. It also protects the objective lens from being immersed into the water drop.

Glass cover slips are very fragile and break easily. They should be handled carefully. They measure 18 or 20 mm square and the glass variety has two thicknesses, Number 1 and Number 2. Number 1 cover glasses are 0.13 - 0.17 mm thick. They are suggested for oil immersion or high resolution work. Number 2 slips are used for general applications and measures 0.17 - 0.25 thick. They are sold by the ounce (120 cover slips per ounce, 20 x 20 mm, Number 2). Glass cover slips can be rinsed and reused many times if handled with extreme care.

When preparing a well slide, one to four drops from the sample container is simply transferred to the depression slide. Higher power objective lenses from your beginning microscope are not used as they will probably get wet when focusing too close to the drop.

The “wet mount” slide is the most common slide preparation for beginning microscopes. It uses a flat slide and a cover slip. To do a wet mount slide, a drop of the sample is placed in the middle of a clean slide and a cover slip is gently lowered over the drop at an angle, with one edge touching the slide first. The liquid is allowed to widen out between the two pieces of glass without pressure applied. If too much liquid is placed on the slide, the cover slip will “float”. This will create a water layer that is too thick. The organisms may be crushed by the cover glass and evaporation will dry up the specimens quickly if too little liquid is used. If you have a well prepared slide, it will last for 15 -30 minutes before it dries up.

Scraping petroleum jelly onto each of the four edges of the cover slip will extend the life of a wet mount slide. The cover slip is placed over the drop of water, with the jelly side down, and it is pressed very lightly to settle it to the slide. This slide may last for a number of days.