Treating moldy and mildewed books with microwave radiation

I had some very smelly mildewed books. I wanted to scan the books, but the mold smell was so strong it made the scan a problem. The strong smell could still be detected even when the books were bagged in 2 thick poly plastic sleeves and taped shut.

The books were nothing valuable, so I decided to treat the books in a microwave oven to see what effect microwave radiation had on mold. Although nothing scientific, here is my test.

I first tested microwaving one of the books in a Tyvek envelope to help encapsulate the spores. I did this for 3 treatments at 1 minute per treatment. I changed envelopes between treatments. That book eventually received 10 minutes of microwaving over a 2 day period.

I also experimented with a second book without the envelope. Further testing was raised to 2 minutes of microwaving. The book gave off visible smoke / steam at 2 minutes of microwaving. Internal temperature of the book reached about 260 degrees, although I could not get an exact reading.

Moldy book after microwave treatment D.D. Teoli Jr.

The books were given a day to rest in open air before any evaluation. Side effects of the treatment gave the pages some rippling, whereas before the treatment, the pages were flat. Both of the books developed a slight bow to the cover, one being worse than the other.  The photo above shows the worse of the 2 books for page rippling and cover bowing. (Scanning rippled pages on a flat bed scanner can be improved with a 5 or 10 pound kettle bell weight on the scanner cover.)

Before treatment the books had a strong mold smell that could be easily detected in a room if the books were kept out in the open.  After treatment, the smell was more of a slight musty odor and hardly detectable when the books were left out. Only upon close handling did you sense a smell.  Some of the stains in the books were intensified from the treatment.

A small amount of microwaving did not warp the pages. But only after extensive microwave treatments did the mold smell dissipate to a large degree. I’d say mold smell was reduced about 70% to 80% as a rough guesstimate. I used a 900 watt microwave oven for all tests.

If you do decide to try microwaving mold or mildew I suggest you do it outside. The microwave oven will dispense some of the moldy smell as it cooks the item. If you are a large institution you can afford a specialized ‘mold room’ with dedicated scanners for mold and the workers can wear hazardous waste outfits with respirators to scan the items. But for the low budget archives…a $59 Walmart microwave dedicated for the job may be able to help. And yes, you should use a dedicated microwave as it will smell moldy inside the oven after you microwave moldy items.

Microwaved page from book D.D. Teoli Jr.

I also tested microwaving an induvial page of a book.

(NMW = no microwave ~ MW = microwaved)

I used (4) 1 minute microwave sessions.  The page showed no rippling. But it only felt slightly warm to the touch. As I understand it, you need something with moisture in it to be microwaved, so I can’t tell if microwaving individual pages does any good for this discussion other than saying the page does not ripple. For the last 1 minute session I added a damp paper towel to the test to add some moisture. If I find a good, moldy page that feels damp to the touch I will update this post.

Update 7.17.19:

The warped books were put in a Tyvek envelop and rested a couple of months.  After the rest the books had returned more or less to their former, un-warped state. Mold smell had had dissipated about 80%.

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DSC06119 lr.jpg

The 2 books tested were high school year books. They both had handwritten notes in ink within. Some of the ink samples seemed to bleed a little and may have migrated to the back of the page or the facing page slightly. It just depended on the type of ink, as some ink samples did not seem to change from the microwave treatment.

Since the books stunk of mold before I started the treatment I didn’t spend much time looking at the handwriting. So I can’t say for sure how it changed from the treatment. Here is some of the handwringing pages in sequence after microwaving.

FastFoto_1042FastFoto_1042_bFastFoto_1043FastFoto_1043_b lrFastFoto_1044 lrFastFoto_1044_b lr

Update 3.16.21:

I inspected the microwave treated books today. They had no detectable odor of mildew and books looked perfect as far as warping. But that does not mean mildew is 100% gone. My nose is only so-so for smells. Still, it is a dramatic improvement if you are willing to let your material age after microwaving.


Daniel D.Teoli Jr. Archival Collection
Daniel D.Teoli Jr. Small Gauge Film Archive
Daniel D.Teoli Jr. Advertising Archive
Daniel D.Teoli Jr. VHS Video Archive
Daniel D.Teoli Jr. Audio Archive
Daniel D.Teoli Jr. Social Documentary Photography


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