Sterile or distilled water is a good mounting liquid but the mounts dry out quickly. Mounting in a stain such as cotton blue can also be used to color pale specimens. Put a drop of mounting solution on the slide and place the specimen in the drop. Lower a cover slip onto the slide, being careful to avoid pushing the specimen to one side or out from under the cover slip. Avoid using too much mounting solution.
Air bubbles can distort images under the microscope.
It is sometimes difficult to recognize air bubbles. Adding the cover slip carefully will keep the number of bubbles to a minimum as would using specimens that are not too thick. Sometimes gentle pressure with a dissecting needle will push the bubbles out from under the cover slip. However, surface features of certain specimens, such as spines on a fungal spore, may actually be easier to see when they are against or in an air bubble. Also, if you focus on the edge of an air bubble, the specimen should almost be in focus, too, needing only a partial turn of the fine-focus knob of the microscope.