Prepared microscope slides, and how to make your own

Slides are the part of microscopy you keep coming back to. A microscope lasts for years, but the slides get used up, broken, filled with pond water and replaced, and the step from looking at a ready-made slide to making your own is the step that turns a present into a hobby. This guide explains what prepared slides are and which set suits whom, the sizes that matter, how to prepare a microscope slide yourself, six beginner specimens with the stain each one needs, how to stay safe with stains, and how to keep the slides you make.

Prepared slides and blank slides

A prepared slide arrives ready to look at. The specimen, such as a section of a plant stem, a smear of blood or a whole insect wing, has been fixed so it doesn't decay, often cut thinner than you can manage at home, stained so its parts stand out, and sealed permanently under a cover slip.

A blank slide is a plain strip of glass for your own specimen, and a cover slip is the thin glass square that goes on top. The cover slip holds a wet specimen flat at an even depth, stops it drying out quickly and keeps liquid off the objective lens. At 400x it's often the difference between a sharp picture and a blur.

Both need a microscope that shines light up through the slide from below, which means a compound microscope such as the Rainbow 2L. Stereo and most digital microscopes light from above and are built for solid objects, so a slide shows up as little more than a shadow.

How prepared slides are made

Commercial slides of tissue go through the same steps a hospital histology lab uses, described in Ohio State University's veterinary histology textbook.

1. The tissue is fixed, usually in formaldehyde, so it keeps its shape.
2. Its water is replaced with alcohol in steps of increasing strength, then the alcohol is cleared with a solvent such as xylene.
3. It's soaked in molten paraffin wax, which sets into a block.
4. A microtome, a precision slicer, cuts sections about 3 to 5 micrometres thick, far thinner than a human hair.
5. The sections are floated on warm water, picked up on slides, cleared of wax and stained, often with haematoxylin and eosin (H&E), which turns nuclei purple and the rest pink.
6. A drop of resin goes on top, then the cover slip, and the resin hardens into a permanent seal.

Kept in their box, well-made slides last for decades. Microbehunter notes that slides mounted in Canada balsam a century ago are still usable, although a 2021 study of museum collections found that balsam slowly yellows and some synthetic resins change within a few years. Levenhuk doesn't say which resin its sets use. Store slides flat, in their box, out of strong sun, and hold them by the edges.

Which prepared slide set to buy

All four of our sets use standard glass slides and fit any compound microscope with stage clips. They differ in how many specimens you get and how advanced those specimens are, and the three Levenhuk sets include blank slides and cover slips for your own.

What comes in each prepared slide set

• Levenhuk N20 NG: 20 prepared, 24 blank, 40 cover slips
• Levenhuk N38 NG: 38 prepared, 24 blank, 40 cover slips
• Levenhuk N80 NG: 80 prepared, 20 blank, 20 cover slips
• Bresser 100-slide set: 100 prepared, no blanks

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Items in the box

• Prepared slides
• Blank slides
• Cover slips

Set	What's in it	Specimens include	Best for
Levenhuk N20 NG	20 prepared, 24 blank, 40 cover slips	Plant and animal cells, onion root mitosis, a fruit fly at three stages, muscle, bone, nerve, frog and human blood	A first set for any compound microscope, ages eight up
Levenhuk N38 NG	38 prepared, 24 blank, 40 cover slips	Everything in the N20 plus Volvox, Euglena and Paramecium, a bee wing, mosquito mouthparts and more plant tissue	Home education, or a step up from the K50 kit
Levenhuk N80 NG	80 prepared, 20 blank, 20 cover slips, illustrated guide	Animals, plants, fungi and everyday things, from Daphnia and Hydra to yeast, cotton fibres and toothpaste	Families who want variety and the guide that explains each slide
Bresser 100-slide set	100 prepared, in a wooden box	School and college biology: human chromosomes, lung, liver and kidney, plant sections, bacteria, diatoms	GCSE and A level students, adult hobbyists, a 1000x microscope

For a child or a first microscope, the N20 NG is the one to start with. If the microscope came with Levenhuk's K50 kit, which has five prepared slides, the N20 is the natural next step and the N38 covers pond life as well.

Slide and cover slip sizes

Almost every slide in the world is the same size, about 3 by 1 inches, so any slide fits any microscope's stage clips. Cover slips vary more, and their thickness matters at high power.

	Standard	Ours
Slide size	76 by 26 mm (3 by 1 inch), or 75 by 25 mm in the ISO version	76 by 25 mm (G50), 76 by 26 mm (Bresser)
Slide thickness	About 1 to 1.2 mm	1.0 to 1.2 mm
Cover slip size	18, 22 or 24 mm square, or longer rectangles such as 24 by 50 mm	24 by 24 mm (G100)
Cover slip thickness	No. 1 is 0.13 to 0.16 mm, No. 1.5 is 0.16 to 0.19 mm	0.13 to 0.17 mm (G100), 0.17 mm (Bresser)
Cavity slides	A shallow dip in the middle for a hanging drop or a thick live specimen	Neither Levenhuk nor our Bresser range makes one

Most objective lenses are designed for a cover slip 0.17 mm thick, the figure engraved on the side of the 40x. The 4x and 10x objectives barely notice the difference, but at 400x a cover slip that's much too thick or too thin softens the image. Microbehunter points out that the 0.17 mm includes the layer of water above the specimen, which is why the slightly thinner No. 1 cover slips sold for hobby use are a good compromise.

How to prepare a microscope slide

There are a handful of ways to put a specimen on a slide, and a beginner needs the first three. Most of what you'll make at home is a temporary wet mount, which lasts until the water dries, often within the hour under the microscope's lamp.

Mount	How it's made	Good for
Wet mount	Specimen in a drop of water or stain, under a cover slip	Pond water, onion skin, pondweed, yeast
Dry mount	Specimen on the slide with no liquid, with or without a cover slip	Hair, pollen, salt and sugar crystals, an insect wing
Smear	A thin film spread across the slide, then usually stained	Cheek cells, blood (on prepared slides), bacteria
Squash	A soft specimen pressed flat under the cover slip	Root tips, banana flesh, soft fruit
Section	A slice thin enough for light to pass through	Stems, roots, leaves; a microtome helps
Permanent mount	Specimen sealed in a mounting medium that sets	Slides you want to keep

The wet mount is the one to learn first. Microbehunter's method, which matches what schools teach for GCSE, is below.

Making a wet mount in four steps

1. Add one dropPut one drop of water or sample in the middle of the slide.

2. Add the specimenIt needs to be thin enough for light to pass through.

3. Lower the cover slipTouch one edge down and lower it at 45 degrees, resting on a needle.

4. Blot the edgeTouch a corner of tissue to any water that seeps out.

1. Put one drop of water, or of your sample liquid, in the middle of a clean slide. Too much water is the usual mistake, because it floats the cover slip and runs onto the lens.
2. Add the specimen to the drop, and make sure it's thin. Light has to pass through it, so a specimen you can see through with the naked eye is about right.
3. Hold a cover slip by its edges, touch one edge to the slide beside the drop and lower it slowly at about 45 degrees, resting the raised edge on a mounting needle or a cocktail stick. The water spreads ahead of the glass and pushes the air out.
4. Touch a corner of tissue to any water that seeps out at the edges, and keep the top of the cover slip dry.

If bubbles get trapped, add a drop of water at one edge of the cover slip and let it draw in, or lift the cover slip and start again. Bubbles look like thick black rings at 40x, and almost everyone mistakes them for cells at first.

Six slides to make at home, and the stain for each

A stain adds colour to parts of a cell that are otherwise almost invisible. These six specimens cover the plant and animal cells in the school syllabus, and everything except the stains is in a kitchen or garden.

Specimen	Stain	Magnification	What you'll see
Onion skin	Iodine	40x to 400x	Brick-shaped cells, about 250 to 400 µm long, each with a nucleus
Cheek cells	Methylene blue	100x to 400x	Flat, irregular cells about 50 µm across with a dark nucleus
Potato starch	Iodine	40x to 400x	Oval grains, mostly 30 to 100 µm, turning blue-black, with rings like a tree
Pondweed leaf	None	100x to 400x	Green chloroplasts, and after a few minutes under the lamp, moving round the cell
Yeast	Methylene blue	400x	Tiny oval cells, some budding; dead cells stain blue
Leaf stomata	None, a varnish print	100x to 400x	The pores on a leaf's underside, each between two bean-shaped guard cells

Onion skin with iodine

Cut an onion into quarters and pull one of the fleshy layers away. On its inner, concave side is a skin as thin as tissue paper. Peel a piece the size of your fingernail with tweezers, lay it flat in a drop of iodine on the slide without folding it, and add a cover slip. The iodine stains the nucleus in each cell darker than the rest, and Wayne's Word, a botany teaching site, gives the cells as about 250 to 400 micrometres long. That's big enough to see the wall of cells at 40x.

Cheek cells with methylene blue

Wipe a clean cotton bud gently along the inside of your own cheek, roll it across the middle of a slide, add a drop of methylene blue and a cover slip, and put the bud straight into a cup of diluted household bleach or disinfectant. Look at 100x first, because the cells are spread thinly. CLEAPSS, the advisory service for school science, says the risk from cheek cells is very small and comes only from other people's samples, so the rule is that everyone handles only their own.

Potato starch with iodine

Scrape the cut surface of a raw potato with a knife and smear the milky juice thinly on a slide. Add a drop of water, a drop of iodine and a cover slip. Iodine turns starch blue-black, which is the classic school test for starch, and the British Pharmacopoeia describes potato starch grains as oval or pear-shaped, usually 30 to 100 micrometres, with rings visible around an off-centre point. Turn the light down to see the rings at 400x.

Pondweed leaf, no stain

Pull a single small leaf from a sprig of Elodea, the pondweed sold for aquariums, and mount it flat in a drop of water. It's only two cells thick, so nothing else is needed. At 400x the green chloroplasts are pressed against the cell walls, and after two or three minutes under the lamp the warmth and light often set them moving round the cell, called cytoplasmic streaming. Never tip Elodea into a pond or stream. It's an invasive species, and the RHS notes that planting it in the wild is an offence, with one kind banned from sale altogether.

Yeast with methylene blue

Stir a pinch of dried yeast into a little warm water with some sugar and leave it 15 minutes. Mix a drop of it with a drop of methylene blue on the slide and look at 400x within a few minutes. Live cells break the dye down and stay pale while dead cells turn blue, but leave it too long and the live ones turn blue too. Our pond life guide has a photo of stained yeast.

Leaf stomata from a nail varnish print

Paint a patch of clear nail varnish about 1 cm square on the underside of a leaf, and let it dry for a few minutes. Press a piece of clear sticky tape over it, peel the tape off, which brings the varnish with it, and stick the tape onto a slide. The varnish holds a print of the leaf's surface, and the stomata show as small mouths, each between two curved guard cells. No cover slip is needed. Oak National Academy's practical uses this method for GCSE.

Once you've done these, salt and sugar crystals sprinkled on sticky tape, a hair, pollen tapped from a flower and a fly's wing make good dry mounts without any stain at all.

Stains to buy, and stains from the kitchen

Iodine and methylene blue cover almost everything a beginner needs. Iodine solution is sold for schools, and dilute methylene blue is sold in aquarium shops as a fish treatment. They work because they stick to particular parts of a cell: iodine to starch and, more faintly, to the nucleus, and methylene blue to the nucleus.

Household colours work too, within limits. McCrone, the microscopy research firm, lists food colouring, egg dyes and washable blue fountain pen ink as stains for living material. They add colour and contrast, but they don't pick out particular structures the way a proper stain does, and what works on one specimen may do nothing on the next. Avoid black ink, which is a suspension of carbon particles rather than a dye.

Using stains safely

The stains used at home are low risk in the dilute strengths sold for the job, and CLEAPSS's student safety sheets give the precautions.

• Iodine. Below a certain strength it isn't classed as hazardous, but even dilute iodine stains skin and clothes. Use a dilute solution, keep it out of the eyes, and if any is swallowed, rinse the mouth and get advice from 111.
• Methylene blue. The powder is harmful, but solutions under 1% in water are low risk. Avoid getting it on the skin; gloves help, and it stains fingers for days.
• Alcohol. Some methods use ethanol or surgical spirit. Ethanol is highly flammable and its vapour can catch light at room temperature, so keep it away from flames, and don't let children handle it.
• Glass. Cover slips are thin enough to snap and cut. Hold them by the edges, keep a pot for broken glass, and supervise children.

Keeping the slides you make

A wet mount dries in an hour or so, but you can keep a good one for longer. Microbehunter's guide to making permanent slides covers the options, which run from easy and short-lived to lasting and fiddly.

• Seal the edges with nail varnish. Paint two or three coats of clear varnish round the edges of the cover slip on a fresh wet mount. It keeps the water in for days rather than minutes. The glass needs to be clean and dry where the varnish goes.
• Glycerine jelly. Melted in a warm water bath and set under the cover slip, it keeps specimens far longer than a wet mount, but it's prone to bubbles and Microbehunter calls it one of the hardest mounting media to use.
• Euparal or Canada balsam. These make proper permanent slides, but the specimen has to be dehydrated in alcohol first, and balsam needs xylene, which is toxic. They're a step for adults once wet mounts feel easy.

Blank slides can be washed in warm soapy water, rinsed and reused many times. Cover slips are cheap and fragile enough that they're usually treated as single-use.

FAQs

How do you prepare a microscope slide?

Put one drop of water in the middle of a clean slide, add a thin specimen, and lower a cover slip over it at an angle so no air is trapped. Blot any water at the edges and look at the lowest power first. For onion skin or starch, use a drop of iodine instead of water.

Do I need cover slips?

For anything wet, yes. Without one, the drop is a curved surface that won't come into focus evenly, it dries in minutes and it can touch the lens at high power. Dry specimens such as crystals or hair can go without.

Can I use prepared slides with a digital or stereo microscope?

Not well. Prepared slides are made to be lit from below and looked at through a compound microscope's 40x to 400x. Stereo and most digital microscopes light from above, so the slide looks dark and the detail is too small at their lower power.

How long do prepared slides last?

Years, often decades, if they're kept flat in their box and handled by the edges. A scratched cover slip or a cracked slide is the usual end.

What's the difference between a blank slide and a cavity slide?

A blank slide is flat. A cavity slide has a shallow dip in the middle for a drop of water with something thick or lively in it, such as a water flea. Small blobs of petroleum jelly under the corners of the cover slip do the same job on a flat slide.

Are microscope slides reusable?

Blank slides are, after a wash in warm soapy water. Prepared slides are permanent and are meant to be kept, not cleaned off. Cover slips are usually thrown away after one use.

Sources

• Microbehunter, wet mounts, cover glass thickness and resolution and making permanent slides.
• Ohio State University, general principles of histotechnology.
• Polymers (2021), ageing of mounting media in microscope slide collections.
• CLEAPSS student safety sheets: human body fluids and tissues, iodine, dyes and indicators and ethanol (PDFs).
• Wayne's Word, onion epidermis; British Pharmacopoeia, potato starch.
• Royal Horticultural Society, Elodea canadensis.
• Oak National Academy, observing stomata.
• McCrone, stains for microscopic specimens.
• Slide set contents from Levenhuk's and Bresser's published product details, checked October 2026.

The two photos of hands at work are AI-generated illustrations. Every view down a microscope on this page is a real photograph, credited beneath it.