Your own Microscope

Your own microscope? Really? Does that seem out of reach? Maybe you’ll feel differently by the time you read through this section.

This tab is for those who want to explore the possibility of buying a microscope and doing their own surface testing. If that’s not for you, skip this section. On the other hand, if you read through this, you may become convinced that buying a microscope would be both useful and cost-effective – and maybe fun, too.

Perhaps your child has a little microscope, or maybe you had one when you were young. If so, you probably have memories of not being able to see much of anything with it. You need a better quality microscope if you’re going to see mold. Let’s talk first about what to buy and where to get it.

Your own microscope – A stereo microscope

This is what you buy if you want to view a flower or a bug or a mold colony on a Petri dish – but not mold spores. The magnification isn’t high enough for mold spores. On my compound (mold) microscope, I use 600X magnification (600 times as big as life). With my stereo microscope, I can only view up to 30 times as big as life. There are other differences between the two types of microscopes, but I will leave that to the microscope dealer to explain.

For a few years in my twenties, each year I’d buy myself a present, and one year it was a stereo microscope. I made this purchase after taking a course in marine biology where I viewed the awesome tiny creatures that lived in a cubic foot of sand at the shoreline of a bay. We put the sand through a metal sieve and gathered up the little creatures, which were placed in a Petri dish containing bay water. The dish was set on the microscope stage, and we could observe the tiny critters moving around.

At that time, I paid about $500 for a new Bausch & Lomb stereomicroscope, which magnified to 30x. Over the years, I have entertained young children with viewing flowers, feathers, leaves, dandelion seeds, their fingers and hair, dog hair, and whatever else we could think of to look at.

You own microscope – a compound microscope

This is the microscope you need for mold investigations. It can magnify much higher than stereo microscopes. This is the microscope that would be used in a high school biology class.

  • Where to buy your microscope – I’d suggest buying from a microscope dealer rather than a company that advertises on-line or on eBay, although one website recommended I have no experience with this site. You might be lucky at Amazon or eBay, but on the other hand, I wouldn’t count on it. I bought 2 15X eyepieces for $20 on eBay, and they were a waste of money. I later spent $100 for 2 15X eyepieces with my dealer, and they were fine. You can get a used student microscope, probably for a few hundred dollars. Or you can get a new microscope. The newer microscopes are of varying quality, probably not as sturdy as a used older microscope, such as a Zeiss, Leica, etc.My microscope dealer tells me that the LED light in the newer ‘scopes is brighter and never needs replacement of a bulb, when compared to older ‘scopes. In my experience, the AC magnetic fields (see EMF section) are lower with LED microscopes than with some of the used older microscopes.

    If you are thinking of buying a used older microscope, bring a gaussmeter (available on-line and from along with you to measure the AC magnetic fields. Avoid instruments that have seriously elevated AC magnetic fields. Most conservative scientists prefer levels of 1 mG or lower for prolonged exposure. Separate the ambient (room) mG levels from the microscope levels. That is, don’t blame a particular microscope when the room itself may be elevated.

    I bought my dealer’s recommendation (AccuScope) and then had him upgrade the lenses to a better quality. He also put 15X eyepieces in the ‘scope for me rather than the more common 10X. The ‘scope was $600 (maybe with a trade-in of my old microscope), and the better optics were $250. I could have bought a satisfactory used student microscope from him for $300-400, but the AC magnetic fields were too high for my comfort. I need to hang on to such brain cells as I have left.

    Tip: The weight of the microscope may be an issue for you, as it is for me. I carry my microscope around and so needed a lighter weight microscope than you might be happy with.


  • Get a binocular microscope with 2 eyepieces, rather than a monocular.
  • Ask for 15x lenses in the eyepieces.
  • The stage should be movable with knobs, not your fingers.
  • If getting an older microscope, get a few extra bulbs.
  • For objectives lenses, get 4X, 10X, and 40X. You don’t need the 100X, which is the oil immersion lens. Labs typically use 600X, which is the magnification you would get with the 40X objective and the 15X eyepiece (40 x 15 = 600), and that’s fine.Tip: The oil immersion lens requires a drop of immersion oil on the microscope slide. The oil contributes to the magnification process. You see 100 x 15 or 1500 times as large as life. A microbiologist told me that I didn’t have to clean the oil off the lens each time. Assuming this is so, that would eliminate one part of the nuisance of working with oil immersion.

    The other part of the nuisance, to me, is that you can’t go back down to a lower magnification on a particular slide if you have oil on the slide. You’d get the other lens oily, and that one would have to be cleaned. What cleans oil off a lens? I wasn’t having much luck with this and was given a tip by someone who knew more than I: saliva.

  • Be sure you know how to turn the microscope on and off before you leave the dealer’s. I have 3 off-on positions on my microscope off-on switch and I still don’t know what 1 of them is for.
  • Be careful of on-line microscope suppliers. The quality might not be what you expect…especially for photography. I’ll talk about taking pictures of what you see later.
Tips for adjusting the microscope
  • A dealer should clean and adjust the microscope prior to selling it to you.
  • A sign of a properly adjusted microscope is that the focus should be about the same at all levels of magnification. In other words, if you focus the ‘scope at 150X and then want to move to the 600X magnification, you shouldn’t have to re-focus, except for a little turning of the fine focus knob. This is one test you can do at the microscope shop before you carry your microscope home.
  • It’s easier to first focus at a lower magnification and then move to a higher magnification.
The parts of the microscope

There are only a few microscope parts you need to know for our purposes. To learn more, you could buy a basic student’s book from the dealer on learning to use a microscope, or do an Internet search for “microscope,” and you’ll find sites that show the parts of a microscope and more detail about how they work. One such site is “The Biology Corner,”, a resource center for science teachers.

  • Eyepieces are what you look through, what you put your eyes next to.
  • Eyepiece lenses -Each eyepiece has a lens in it. These lenses typically are 10X, which stands for 10 times magnification, so looking through a 10X eyepiece makes an object look 10 times as large as it really is. The magnification number will be stamped on the eyepiece. As noted above, I like eyepieces with 15X lenses which are better for distinguishing mold spores.
  • Objectives -Midway on the microscope, you’ll see three or four metal cylindrical “objectives,” screwed into a circular metal plate known as the “revolving nosepiece.” You can turn the nosepiece so that any one of the objectives clicks into place, that is, pointing directly downward toward a microscope slide.There is a number printed on the side of each objective. This number gives you the strength of the magnification for that objective. A 10X objective multiples the image 10-fold. A 40X objective multiples it 40 times as large as life.To determine the total magnification of the image, multiply the magnification of the eyepiece by the magnification in the objective. For example, 10X times 40X would be 400X total magnification, or 400X as large as life. 15X times 40X would give you 600 times as large as life. I worked in the beginning at 400X but years ago went to 600X. From here on, I’ll speak only in terms of 600X magnification.
  • An electric light source is built into the microscope. The bulb is usually at the bottom of a compound microscope, so the light passes up through the slide and then up through the objective and through the eyepieces to enable you to view what’s on the slide.Tip: If you get a microscope that has a bulb that will need to be replaced eventually, hold the bulb with a tissue so that oil from your fingers doesn’t get on the bulb. The oil could shorten the life of the bulb. Ask how to change the bulb when you buy your used microscope.
  • The microscope also has a fuse. I’ve never had a fuse burn out, but if it did, I was told that I could get another at a local electrical supply house.
  • Sliding switch to control the amount of light is near the base of the microscope. It sometimes gets moved when I pack up the microscope, throwing the amount of light off. I adjust that switch as needed to increase or decrease the amount of light coming through so that I can better view the material on the slide.
  • Microscope slides are 3”x 1” pieces of clear glass. If you were looking at a tape sample under the microscope, you’d put the tape on a microscope slide and then position the slide on a horizontal platform (the stage) on the microscope.
  • The microscope should have a set of knobs on either side near the base. There is an inner knob, which is the coarse focus knob, and an outer knob, the fine focus knob. If focus gets really off, you’ll use the coarse focus knob to get back in the ballpark. The fine focus knob  is used for more detailed focusing. Since there is a set of knobs on both sides of the microscope, you can use either your left or your right hand to focus.Tip: Mold structures are 3-dimensional, so you’ll continuing be slightly turning the fine focus back and forth.
  • Knobs are also attached to the underside of the stage so that you can move the stage backward and forward and from side to side. Since the glass slide sits on the stage, you use these knobs to view different areas of the material on the slide. These knobs are set one on top of another.Tip: These knobs are on only one side of the microscope. If you are right-handed, you’ll want them on the right side.

    Tip: Some microscopes combine the large and small knobs into one, which will take some getting used to. The large knob function has more resistance and is a little harder to turn. Then, do the fine tuning with the easier-to-turn function. I prefer the traditional type of knobs, where you have a coarse adjustment knob and a fine adjustment knob.

  • There are other little knobs around the stage that have their own jobs. One set centers the image you are viewing. These little knobs are rarely needed. You can try them and see what they do. Just remember the reference point that they came set to, so you can return the setting to that point.
Your own microscope: Getting started
  • You need to have something to look at first. In order to better view what’s on the slide, you first put a drop of stain on the slide before positioning the tape sample. The stain gets absorbed by the mold, thereby coloring the mold and making it easier to see. I’ll discuss the stain below.Tip: I rarely if ever use cover slips (placed over the sample on a slide). Scotch tape is a better tool for checking surfaces for mold. Touch the tape to the surface, put a drop of stain on the slide, and smooth the tape over the stain. I prefer Scotch-brand MultiTask tape, which is clear and glossy and sturdier than some other clear tapes. A second choice would be Scotch-brand transparent tape.
  • Next, focus the eyepieces to your eyes. The focus on the left eye may be different from the focus on the right eye. Here’s how to coordinate them:Look through the right eyepiece and use the fine focus to make the image of what you are viewing crisp and clear. Then close your right eye and view the image with your left eye. The left should be just as clear as the right. If the left is blurry, turn the base of the left eyepiece until the image is clear. Then you will see clearly with both eyes.

    You should also manually adjust the eyepieces so that they are the proper distance apart for your eyes. They move farther apart or closer together.

    Tip: If you only see a partial picture when looking through your left eye, slide the eye pieces closer together or farther apart to match the distance between your eyes.

Your own microscope: Training

Granted, I had some microbiology classes under my belt, but when I started my business in 1994, mold wasn’t yet on the horizon. None of the courses I had taken addressed mold in a home. I had to teach myself to observe and identify mold. You can do the same.

Question: Isn’t there a course I can take to speed up the process?

Answer: I don’t know. The only courses I have heard of seem to go into far more detail than you would need. You might come out of such a course with your head spinning and still not know how to do a simple mold assessment and what fungi to look for. You and I don’t need to be microbiologists. We just need to be down-and-dirty mold inspectors, and I am teaching you how to be that, here.

Tip: If you’d like some practice slides of Aspergillus, Penicillium, Stachybotrys, and a few other molds that I might have on hand, you could send a check for $15, made out to EnviroHealth, and I’ll be glad to send you some prepared slides. These are homemade slides and may dry out after a few months, but that doesn’t matter because you’ll be making your own soon enough. You would have to put your own drop of stain (or even water) on the slide to view it. For some reason, a slide soon gets cloudy (within 10 minutes or so). You can still see the mold, but the slide is better used immediately. I’ve tried adding isopropyl alcohol to the stain, but it still gets cloudy.

Gather your supplies
  • You’ll find ¾” Scotch-brand clear, shiny MultiTask tape or similar store brand in any office supply store. You’ll find this near the Magic Tape, but don’t get Magic Tape, because the light won’t pass through it, and you’ll see just a cloud-like blur. Transparent tape looks clear, but it is not as good to work with as MultiTask. Avoid invisible tape. Avoid packing tape.
  • Buy 3”x 1” microscope slides from your dealer or on-line. They come in boxes of 100, and I pay under $10 a box. I pay a little more to get them with white or frosted ends, so that I can pencil in a number on the end. (I like the white better than frosted, because I can see the penciled numbers better, but frosted is fine, too.)
  • I re-use slides. At my office, I peel off and discard the used scotch tape. Then I wipe off the slides with a damp paper towel. Finally, I use an eraser to remove the numbers. Then the slides are ready to be used again.I used to soak the used slides in hydrogen peroxide overnight to kill any mold on them. Then, through experience, I learned that soaking wasn’t needed. Just cleaning off a dirty glass surface with a damp paper towel was sufficient.
  • Stain your sample. Mold spores are easier to pick out from background debris if you put a drop of colored stain on the slide under the tape. I use a fuchsin (pink) stain, but many microbiologists prefer cotton phenol blue, a blue stain which is better for photography if you eventually want to take pictures of what you see. The fuchsin costs less and doesn’t give me a minor headache, like the blue stain does.Tip: You might have trouble purchasing stain, because some supply houses only sell to businesses. If you can’t locate stain or it’s too costly, send me a stamped, self-addressed envelope, and I’ll send you a little fuchsin powder. A little goes a long way, and the supply I bought from Clarkson Laboratory & Supply, 1-619-425-1932, for around $30 (years back), should last me roughly 500 years, if not 1000. Please email me for a mailing address,

    Tip: I was originally told to add distilled water, vodka (my guess is to keep down the growth of bacteria), and glycerin to a tiny bit of the fuchsin powder, like the amount on the head of a pin. Since then, I’ve at times been close to running out of the solution on a job, so I added tap water to the remaining stain solution, and this worked fine, just being a little lighter in tone than usual but workable. Now, even when first mixing the stain, I just add tap water.

    Tip: I don’t carry fuchsin powder around, because it stains very easily. Imagine a client’s beige carpet with bright pink stain on it! Instead, I keep a second little medicine bottle (with a dropper), containing water and fuchsin concentrate (fuchsin and water) at my office. I add a few drops of this solution to a second medicine bottle filled with tap water. It’s a homemade stain, but it’s cheap and it works. Over the years, I’ve easily saved a few thousand dollars from buying prepared stain. I used to pay about $45 for a small medicine bottle of prepared fuschin stain, and then I learned I could buy a whole bottle of fuschin powder for $27! I’m still working off that same bottle of powder.

    Tip: I hold the medicine bottle up to the light to gauge the color of the water, so that it’s not too light or too dark. You’ll soon get a feel for what shade you prefer for viewing mold, even when viewing the solution through the dark medicine bottle.

  • Tip: Plan ahead for spills, because they will happen. I set the medicine bottle inside something like a plastic box or in the doughnut hole of a small roll of duct tape. I always have a folded plastic bag or piece of Naugahyde (from a fabric store) under my microscope and work area. A colleague once paid to replace the white rug at a client’s house. A few times I had a bottle of stain tip over, and I was very glad to have the Naugahyde underneath and not the finished surface of the client’s dining room table.Tip: Screw on the top when the bottle is not in use. It’s easy to get lazy on this subject, but after you tip the bottle over accidentally a few times and are relieved that the top was on, you discipline yourself because you know that accidents happen. A client’s cat once knocked an expensive piece of equipment off a table.

    Tip: Medicine bottles with glass droppers can be a challenge to locate. If your local health food store doesn’t have them, one sources is Exotic Fragrances, 1-877-787-3645,, $10-$12 for a dozen 1 oz brown glass bottles with glass droppers.

  • Cotton phenol blue stain is an alternative stain, said to be better for photography. This would have to be ordered from a microbiological supply house. Cotton phenol blue gives me a slight headache, so I mostly avoid it.
Taking a tape sample
  • Take about a piece of clear glossy tape about 3 inches long. Use the first two fingers of one hand to hold the tape by the two ends, sticky side out.
  • Firmly press the sticky side to the surface you want to test. If the surface has obvious mold, press the tape lightly to avoid getting too much material on the tape. Or, press at the outer edges of the mold growth.
  • If you pick up a wood splinter or other larger material on the tape, knock larger debris off. A 3-dimensional piece of grit will just make a bump under the tape and throw off your focus at that area. Don’t stick your finger into the middle of obvious mold, of course.
  • Some surfaces have a lot of dirt on them, and you want to avoid getting a tape with a dark mass on it. It’s hard to see mold spores amidst a jumble of dust and other particulates, even if the light could get through the mass. If you just touch the tape lightly to the surface so that not much dirt adheres, you should see spores more easily.Tip: My suggestion is to test a surface where dust doesn’t collect so easily. For example, sample on the underside of a lower wood shelf rather than on the upper side in a basement.
  • If there’s too much debris on a slide, maneuver the view to areas that aren’t so dense with debris. If those areas are free of spores, then there is a better chance that the dirtier areas are fairly clear, too.Tip: Sometimes you want to sample something that has a lot of debris (such as an AC filter). Maybe you will be able to see clear signs of mold growth, but maybe not. In such a case, I might touch the tape to multiple areas on a Petri dish with mold food in it. It may be easier to get a sense of how much and what kinds of mold are present through growing out the spores rather than looking under the microscope. In one sample where I hadn’t seen spores under the microscope, plenty of Aspergillus niger colonies grew, which was a lesson that when there is a lot of debris, you just might not be able to see the mold spores.

    Tip: Examining a tape touched to the inside of ductwork, either through an access hole or inside a vent, may also provide a clue about the amount of mold in the system.

  • What you should have now is a 3” piece of tape that has nothing but fingerprints on the ends and some debris in the center of the tape. Even a half inch or less of debris is fine, less than the size of a dime. When the debris is magnified 600 times, the area could look as big as a football field.Tip: To later find your way back to the mold on the tape, you can mark the spot on the tape with a ballpoint pen. Make a little circle around the area.
Staining the sample

Now that you have your tape sample, you’re ready to stain the sample.

  • Using the eyedropper, place a drop of fuchsin stain in the center of the microscope slide. If you have no stain, just use water.
  • Stick one end of the tape near the white or opaque end of the slide. Position the end so that when the tape is flat on the slide, the debris on the tape will be approximately in the center of the slide.
  • Hold the free end of the tape with one hand. With a finger of the other hand, smooth the tape down lightly over the stain. You might have to lift the tape and smooth it again to spread the stain out under the debris.
  • When enough of the debris has stain on it, firmly smooth the entire tape down to eliminate most of the air bubbles.
  • If any stain seeped out from under the tape, blot it with a tissue, so the microscope objective doesn’t get wet from the stain.Tip: If an objective does get wet, blot the bottom of the objective with tissue paper as best you can. You may have to wait until the glass completely dries before being about to focus properly again.
  • If any tape is hanging over the end of the slide, slice it off against the slide. Otherwise, the tape may stick to the microscope stage and interfere with moving the slide around.
  • View your sample, using the fine focus (or first, the coarse focus if necessary) and moving the tape around on the stage using the knobs for horizontal and vertical movement. Congratulations! You’ve passed the first milestone!
  • Now that we’ve gone through preparing a single sample, let’s back up a minute and talk about how to take multiple samples and not mix them up.
Keeping multiple samples straight
  • As you walk around taking samples, number the slides and write a description of the number in your notebook. For example,1. inside kitchen sink cabinet
    2. half bath sink cabinet
    3. main bath sink cabinet on right
    4. main bath sink cabinet on left
    5. base molding under hall window
    6. discolored area on bedroom ceiling, and so on.

    Tip: To number the slides, pencil in the number on the white or opaque end of the slide. If you use ink to write in the number, you won’t be able to erase it when recycling the slide. I use small numbers instead of descriptive terminology on the slides. What I write, I have to erase.

    Tip: What I typically do is to make my list of where I want to sample first. I’ll walk around a basement and jot down the surfaces I want to sample, room by room if the basement is partially finished. Then I’ll number ten or twenty slides or more slides and follow my list in taking samples.

    Tip: I stain the slides when I get  back to the microscope because of the risk of a spill with the stain. Think of a nice red spot on a ceramic floor tile.

    I place the tape on a slide without the stain. Later, back at the microscope, I’ll peel the tape back and apply a drop of stain, and then smooth the tape back over the stain. An added benefit of this technique, as mentioned above, is that stains get cloudy after 5-10 minutes, so I’d rather look at freshly stained slides than slides that were stained a half hour ago. Often, if my client is sitting next to me watching what I am looking at on my computer monitor, I’ll ask the client to stain the slides, to speed up the process.

  • Another trick is not to take slides around with you, either (in case they drop and break), but to take a gallon size zipper bag, and, using a permanent marker (do this outside, to lessen the exposure to marker fumes), number from 1-10 on the left and from 11-20 on the right. Now you can put your tape down in order, leaving one end hanging over the edge of the bag. When you go to the microscope, it’s a simple step to peel off the tape and put it on a microscope slide (with a drop of stain) with the same number as the number on the bag. The debris on the tape will stick to the tape, not to the plastic bag, when you pull the tape off the bag.
  • Sometimes I just work from the slides without staining them, or with just staining the ones I’m not sure about. You can’t see the mold as clearly without staining it, but often I can see enough to know what I’m looking at. That comes with experience. But if in doubt, use the stain. I keep the stain nearby and usually use it.
Using the microscope
  • Set up a comfortable viewing area on a table or desk near an electrical outlet. My office microscope “chair” is one of those backless seats where you sit on one upholstered pad and your knees go on the lower pad. Over extended periods of microscope work, I appreciate different positions from my computer chair.
  • Plug in your microscope and turn it on.
  • Place the stained microscope slide on the stage, using the clip to secure it.
  • Look at the numbers on the three or four objectives on your microscope. Choose the objective marked 4X. With your 15X ocular lens, the 10X objective will give you 60X magnification (4 x 15).
  • Use the coarse focus knob to zero in on the debris.
  • Once the debris is clear, change to the 10X objective, which will bring you up to 150X magnification. Fine focus. At this magnification, you will see debris and mold more clearly but the mold will still be too small for study purposes.
  • Lastly, change to the 40X magnification and fine focus at 600X (40 x 15). You shouldn’t have to touch the coarse adjustment knobs to focus at 150X or 600X. If you do, your microscope needs adjustment. Take it to a dealer.Tip: Do you see large round shadowy areas on the slide? They are probably air bubbles from the stain. I mistook them for microorganisms the first time I saw them under a microscope, and lots of my clients have, too. Mold spores are much smaller than air bubbles.

    Tip:  Sometimes not matter how hard I try to focus, the slide remains blurry. If all else fails, see if you placed the slide upside-down on the stage, with the tape on the underside of the slide. I’ve done it more than a few times.

Recognizing mold under your microscope

At 600x, you’ll be able to see mold. If you know what to look for, you’ll find it sooner or later. Let me share my early experience with you.

I had had some background biology and microbiology science classes in college and grad school, and more when I started environmental home inspection studies, beginning in 1994. Those were the days before mold became a hot topic, and not much class time was devoted to the subject of mold inside houses.

Around 1996, I found a reference book which would become my classroom. Identifying Filamentous Fungi: A Clinical Laboratory Handbook, by Guy St-Germain and Richard Summerbell, can be ordered from Star Publishing Company, 1-650-591-3505. There are pictures and descriptions of what mold looks like under the microscope, so you can match what you’re seeing with the pictures. The book gives several ways of identifying mold, and I have spent hours and hours with that book. Your progress will be much faster, because I am going to tell you the shortcuts. You’d benefit from the book, but you’ll find enough here to get you started. (The book doesn’t address allergenic, neurological, and inflammatory aspects of mold exposure – rather, the  infectious aspects.)

The first mold I identified microscopically was green bread mold, Penicillium. I was able to focus in and see the chains of spherical spores easily. I knew that I needed to find a fruiting body that produces the spores to be sure I was seeing Penicillium. There were so many spores on the slide I was viewing that I couldn’t see fruiting bodies for quite a while. Finally, I figured I’d look around the edges of the mold, where the growth wasn’t so dense. Suddenly, I saw a branch-like fruiting body with chains of spores coming off the tips. How exciting! How delicate, how beautiful! My first positive identification. I was on the way.

Since those days, I have identified a lot of the molds in the St-Germain-Summerbell book. When I started, I’d see a new mold and say, “And who are YOU?” and then leaf through the book to see if I could identify the mold. I’d look for the fruiting bodies, for the shapes of the spores, for the colors of the colonies (if I was growing them), and for other identifying characteristics that the book listed. How exciting to see Trichoderma, Mucor, Rhizopus, Syncephalastrum, right under my microscope! And to find other molds, one after the other. Many of these molds have to be grown in Petri dishes from air samples; you typically won’t find them on tape samples.

The good news is that there are only about a half dozen common indoor molds associated with dampness or water leakage conditions that can be captured on tape. Thus, while I had a lot of gratification from learning to identify other molds, most of what I saw at houses was Alternaria, Aspergillus, Chaetomium, Cladosporium, Penicillium, Stachybotrys, and sometimes Trichoderma.

These common indoor molds can be found through tape sampling. Unless you decide to get into the culture plate air sampling business, you probably won’t find too many fungi beyond these…and maybe, for our purposes, you don’t need to.

As an alternative to buying the St-Germain-Summerbell book, you can also find photographs of common fungi in the previous tab and on-line.  An Internet search on various molds brings up an endless list of sites relating to mold and to specific kinds of mold. Include “microscope picture” and the name of the mold in your search terms, and you’ll be in business.

Tip: Many molds don’t produce spores, and all you see under the microscope is a bunch of branches. These may be “sterile fungi” or “non-sporulating fungi,” which may or may not be allergenic. Little is known about them, and there are many, many species, often with minor variations. Labs generally don’t further differentiate them, if they are listed at all. One microbiology professor called them “the white fuzzies.”

The field of mycology (a branch of botany dealing with fungi) is vast. One day I read about a book identifying molds growing on telephone poles. Checking out telephone pole fungi sounded like a fun thing to do, so I ordered a copy of the book. Forget it. Trying to get conversant with the tiny distinguishing aspects of 1000 similar-looking molds was definitely not fun. I’ll leave telephone poles to the microbiologists.

Nor do I try to distinguish among even the common species of common molds, such as Aspergillus. I leave that up to the microbiologists, should a client need to know. Sometimes the report comes back listing some species that aren’t even in my reference books. There are whole books written just on Aspergillus species. There’s also a website,

Pictures of mold under your microscope
  • Check out the tab for Mold Photos.
  • Check out the tab for my Cheat Sheet on Mold. This is the hand-drawn summary page I use with my clients.
  • You can find numerous websites providing photos of what different fungi look like under the microscope. Just do a search on the mold you want: “Penicillium + picture + microscope.” Dennis Kunkel, has exceptional artful pictures of mold using an electron microscope.
What common molds look like under your own microscope

One or more of these are the main players at most houses with mold. A tip is that you will be looking for regular shapes when you look for mold spores. If you can play the toddler game of putting the square peg into the square hole, you’ll do fine…only look for the spheres, the club-shaped spores, the lemon-shaped spores, the grape-shaped spores, ovoid-shaped spores, and the elongated soccer-ball-shaped spores.

Alternaria – club-like spores, sometimes in short chains; the largest of the common spores

Aspergillus – chains of spherical spores, produced from fruiting bodies that look like flower heads, lollipops, or pompoms

Chaetomium – lemon-shaped spores produced in large spider- shaped structures

Cladosporium – varying shapes of spores, such as narrow ovoid (three-dimensional oval) with black connection points on ends where they once joined to other spores, bi- cellular spores (spores with two cells), and shield-shaped spores. The black connection points are known as “birth scars.” Is that not sweet?

Penicillium – chains of spherical spores, extending off the ends of brush-like structures

Stachybotrys – black grape-like spores, at the end of a stalk like a bunch of balloons or grapes. “Stachy-botrys” means “grapes-on-a-stick” in Latin.

Trichoderma – spherical spores, often in a green cluster, with branch-like hyphae (growth structures, like branches) that may have cross-like branch ends

Ulocladium – segmented and broadly ovoid, somewhat like an elongated berry or soccer ball

And then, there are other molds, such as Acremonium, Mucor, and Rhizopus, but in the average house, I find the ones listed above to be more common in tape “finds.”

Some of my observations on the common indoor molds
  • Alternaria, a dark grayish brown mold, is also associated with asthmatic or allergic reactions. One young chap discovered the mold growing on the back wall of his closet when he had an asthmatic reaction at the closet. The closet backed the master bathroom shower where there was a chronic leak due to missing sealant on tile under the entry ledge. The builder repaired the leak and replaced the drywall in the closet, but the boy still reacted.I was called in and walked the builder through how to clean the area properly. The builder hadn’t replaced the wood support to the shower pan. The wood had been chronically wet and was a heavy source of Alternaria. Having another go with demolition and cleaning resolved the boy’s asthmatic reactions. This time, the parents opted for a shower enclosure, rather than replacement tiles, to reduce the risk of future leakage and demolition.
  • Aspergillus and Penicillium are often found wherever moisture is found: in damp basements, under steps to the basement, behind finished basement walls, in attics with inadequate ventilation and too much moisture, at plumbing or roof leaks, inside sink cabinets, below-grade on wood or OSB (oriented stand board) in new construction, on AC coils and in contaminated ductwork, on ceilings and insulation in damp crawl spaces, growing on books and clothing stored in basements, and on furniture in houses shut up in a humid season.Sometimes, floor cleaning activities result in water continually being sloshed against molding. Asp-Pen could grow under that molding. Don’t push water against molding; draw the damp mop along and away from the molding.

    Because Aspergillus and Penicillium spores look similar, because other fungi can also have spherical spores, and because characteristic fruiting bodies aren’t always seen, the general term for these molds is “Aspergillus or Penicillium-like,” or, simply, “Asp-Pen.” If I see a half dozen stray spherical spores on a tape sample, I don’t know whether they belong to Aspergillus or Penicillium (or some other mold producing spherical spores). I call them “A-P” in my notes.

    Health effects from either Aspergillus or Penicillium can be similar. If a few spores are inhaled, there may be allergic or asthmatic responses. If there is a lot of growth, and gases are breathed in, maybe there would be neurological responses, such as headache, depression, or inability to concentrate. The immune system may become compromised from being in a state of alert at home.

    If mycotoxins or microparticles are inhaled (see the Cutting Edge tab), an inflammatory cascade may be initiated. If someone lives in a very moldy basement, maybe there could eventually be a fungal infection of the lungs.

    When growing on a Petri dish, both molds have various colors, ranging from green to white, orange, yellow, or black (Aspergillus niger). I started colored-pencil drawings of the coloration of Penicillium colonies and filled up three pages of variations before I gave up. The colors of some colonies were exquisite. Coloration can change when the mold is grown on different types of nutrients as well.

    Under a microscope you’ll see all sorts of differentiations, from the size and texture of the mold spores to how much dye they absorb, to the width, texture, and segmentation of the hyphae or differences in size, shape and textures of the structures that produce the spores. It is these details that a lab technician looks at to help determine the kind of mold being cultured. Science is moving on, however, to computerized DNA testing, which is more precise, with results available much quicker, and for a fancier price.

  • Chaetomium is another black allergenic mold, usually associated with leaks. This is the mold that frequently is present on a few rafters in the attic or on some ceiling joists in the basement. Many times, it is old, dried out mold, especially in the attic. Under the microscope, I see just broken up pieces of hyphae, with no spores. This is non-viable mold; it can’t grow again. You could just damp-wipe it off with Borax solution, though a dark stain may remain. Or, spray it with Concrobium Mold Stain Remover to remove the stain.
  • Cladosporium is an allergenic mold that also can give off some toxins. Because its spores have multiple shapes, I pick out a few distinctive ones to look for under the microscope. I know the mold is Cladosporium if I see elongated oval spores with black dots on either end, or if I see bi-cellular spores (spores with two cells) or the shield-shaped spores. Cladosporium is the black mold that often grows on windows or windowsills, on the bathroom ceiling, near the top corners in a closet on an outside wall, at AC coils or in insulation, and on attic sheathing if there is too much moisture and too little ventilation.In my experience, Cladosporium spores are well-behaved. That is, they don’t become airborne readily from growth areas. You can nevertheless have elevated levels inside a house if windows are opened, because Cladosporium blows in from the outside. Unless you are allergic to Cladosporium, these spores mean little. They would float down to surfaces and be cleaned up by damp-dusting or HEPA-vacuuming. If you sprinkle a little Borax on a damp sponge and wipe off a windowsill, you don’t have to worry about Cladosporium spores spreading throughout the room.
  • Stachybotrys likes wet surroundings. It needs water and prolonged wetness to grow. Stachybotrys is more likely to grow where there has been a flood or a leak than in a chronically damp basement. It likes drywall, so if you see lots of black mold growing on wet, or previously wet, drywall, there’s a good chance it’s Stachybotrys. I have only once seen it grow on concrete. At one house, I found it practically covering the back wall of a bathroom sink cabinet due to a chronic leak at the faucet fixture. The lesson is: Fix leaks right away. Here the cabinet was a loss.I sometimes find Stachybotrys or other molds under the edges of molding in bathrooms. If there is a gap between the bottom of the molding and the floor covering, look into a low-VOC caulk that could seal the gap.

    Stachybotrys has been associated with lung hemorrhaging and blood conditions in young children. There is some evidence for neurological damage due to chronic exposure to mycotoxins from some species of Stachybotrys.

    Stachybotrys gives off many compounds, among them close to 200 varieties of trichothecenes, which are potent mycotoxins.

  • Trichoderma is a fast-growing green mold that also can give off trichothecenes. A few of my clients have been extremely sensitive to this mold. Occasionally I see it in tape samples, not very often. For me, the tell-tale signs of Trichoderma under a microscope are green bunches of clumped spores, somewhat like clusters of tiny grapes. The spores grow out of cross-like branches, best seen at the end of branch-like structure.A favorite place for Trichoderma growth is on basement subflooring around water pipes with condensation. Look for forest green mold growing in wood grains.
  • Ulocladium is another moisture-loving black mold commonly found in leak areas. I’ve seen it covering the sheathing in an attic lacking adequate ventilation. Spores look like elongated soccer balls or berries.
  • Mucor, Rhizopus, and others are genera (plural of genus) that like chronic dampness, either long-term ambient dampness or shorter-term floods and leaks that weren’t cleaned up right away.
  • Other unidentified molds may be found indoors. In my notes, I sometimes use a designation, “cwm” or “common wood mold.” That’s a term for molds I see here and there on wood but don’t know what they are. The client could pay the lab fee and have the sample sent out for identification, or we could just say, “If there’s mold, clean it up.” The latter is the usual approach. I tell the client that the good news is that the mold is not on the list of common indoor molds that may affect health, at least not yet. Actually, some of these common wood molds are very hard to scrub off. This is the type of mold that I would just paint over and not think twice about it.

Aside from sewage leaks, not much attention is paid to bacteria. As research progresses, one of my microbiology professors may be proved right, that bacteria growing in homes may prove to be of more importance for health than mold. Or, mold and bacteria could interact or be synergistic, that is, health effects from the sum of their interactions are greater than the sum of either one’s added together.

Bacteria are single-celled organisms that are smaller than mold when viewed under a microscope and obtain their nourishment by dissolving and absorbing organic matter. At 600x, there might be a film visible on the tape, with lots of little rods or ovals in the film. You might only know that bacteria are present by seeing the edge of the film, kind of like the edge of a cloud. A different stain should be used for bacteria (such as crystal violet stain).

Bacteria need food and water to grow, but they die or form spores when they dry out, so they are more often found in chronically wet or damp areas. Like mold, bacteria give off toxins and other substances, contributing to health reactions similar to those from mold exposure. Bacteria can grow in films, spreading over a surface, with the film taking on characteristics of its own. This film is known as a “biofilm.”

Bacteria grow faster than mold. If there is water damage, bacteria will be on the scene before mold. For example, Stachybotrys often grows together with Streptomyces.


Biofilms are a relatively recent field of study, thanks to new developments in laser microscopy. Biofilms are an aggregation of bacteria, mold, or a mix. Listen to this definition that sounds right out of science fiction:

“Biofilm: An aggregate of microbes with a distinct architecture. A biofilm is like a tiny city in which microbial cells, each only a micrometer or two long, form towers that can be hundreds of micrometers high. The “streets” between the towers are really fluid-filled channels that bring in nutrients, oxygen and other necessities for live biofilm communities,” from the website,

Biofilms are common health hazards with various medical conditions, such as in periodontal disease and cystic fibrosis pneumonia, as well as in contamination of urinary catheters and medical implants. Millions of people are affected annually by biofilms, whether at home, in medical equipment, in implants of one sort of other, etc.

Biofilms are also present in the environment, such as inside water pipes. Chlorine doesn’t kill bacterial films growing in and around flaking pipe interiors. Some communities are adding ammonia to public water to try to get rid of bacteria missed by chlorine, as well as to cut down on levels of carcinogenic chlorine by-products. An Internet search on “biofilms” will bring up many interesting sites.

Well! Did I convince you that working with your own microscope would not be beyond the realm of possibility? You can do this! I remember seeing a new mold under the microscope and asking, “And who are you?” and then turning to my reference book to look for a matching picture. My reference was, and is, Identifying Filamentous Fungi – A Clinical Laboratory Handbook by Guy St-Germain and Richard Summerbell, available from Star Publishing Company, 650-591-3505. Are you up for a new hobby? for a new tool?

Let’s go now to the tab on water quality for drinking and bathing. Meet me there!

Improve your indoor air and water quality and reduce exposure to mold and electromagnetic fields