Microwave Magma: a lava flow of liquid Pyrex

A guy who repairs microwave ovens once told me that an oven burned a hole through a Pyrex measuring cup. The cup had boiled dry, and apparently the microwaves attacked the glass. Yet glass is mostly transparent to microwaves, so it shouldn't heat up. WTF?!!
 

Then I remembered a little trick that physics teachers perform. First they connect a glass rod to 120VAC cables. Then they heat the glass rod with a blow torch until it becomes red hot between the electrical connections. Glass is full of sodium or boron ions (charged atoms,) and glass becomes a conductor when softened. The ion charges become unlocked and movable. As it's heated with the torch, the red hot glass suddenly draws significant current from the electric outlet, it turns yellow hot, then white, then incandescent blue-white. It burns in half (if your circuit breaker doesn't trip first!) For a moment it acts like a light-bulb, but with a glass as the glowing filament.
 

Hmmm. So... if something were to heat a tiny spot on the glass to nearly red hot... the glass would become a good absorber of microwaves? It then might quickly become white hot, heating the surrounding glass to red hot, which would also absorb microwaves and begin heating. An "outbreak" of melting would occur, like a microwave-powered forest fire slowly moving through the glass. It only needs a trigger. (Also the oven needs to be empty of every other object, otherwise most of the wattage will end up elsewhere, rather than in the glass we wish to melt.)
 

Torch a little hotspot...

...pop it in the ol' nuker

...sit back and enjoy.

It works great! Just use some method to heat a small spot on the rim of a pyrex custard dish to red hot, slam it instantly into the oven and hit "start." The tiny red glow will increase wildly. Just remember to shut it down before the advancing "lava flow" runs to the bottom of your oven and burns off the paint. Obviously this is somewhat dangerous as a demo. If you don't already know the hazards (such as trapped internal strains and high-velocity shrapnel), then messing with this procedure would be extremely Unwise.
 

NOTICE: this one requires a source of welders' Argon.
 

Hobbyists discovered the joys of high voltage Argon a few years ago. Shoot foot-long lighting bolts from your fingers!
 

Ah, since a microwave oven is a high voltage environment, what will happen? I tried nuking some pure argon in a round flask. Nuthin. RATS! But years later at a hobbyist meeting I wondered what would happen if the "plasma pool" experiment was performed in pure argon? I set up a piece of Carbon Veil (carbon fibers) in a shot glass, inside a trash bag, inside my microwave oven. I inflated it with argon and ran the oven. A spherical white lightning ball winked into existence at the carbon, then rose upwards buzzing. Yay! The Argon needs a sharp conductive "igniter" to get going.
 

During WEIRD GENIUS REAL SCIENCE I tried some extremely pure argon in a spherical glass flask with a tiny piece of aluminum foil as an igniter inside. (The argon used previously had quite a bit of air mixed in.) Hit the button. WAAAA! THE WHOLE GLASS FLASK FILLS WITH BLUE WHITE LIGHTNING! Tiny bright lightning filaments! And afterwards the flask was full of transparent orange gas.
 

So next, I put a little bit of argon in a white kitchen trash bag, threw in a piece of carbon fiber, then squeezed out the argon (to flush any nitrogen totally out.) Then I filled half the bag with argon, tied it off with a plastic tie, and stuffed it into the oven. Close the door. Hit the start button. Ten seconds of stunning noise, lights, and patterns, and the small audience broke into spontaneous applause, because...

• First the ENTIRE OVEN FILLED WITH JITTERING LIGHTING BOLTS
• Next the bag started melting and collapsing, holes appeared
• The lightning spewed right into the air through the holes as the bag shrunk
• The lightning remaining in the bag turned into bright turquoise plasma
• As the bag entirely collapsed, brilliant plasma amoebas crawled frantically around, burning the bag and finding every last bit of remaining argon.
• Silence. Darkness. The stunned crowd cheers.

The patterns are easily visible with white kitchen trash bags, although a clear plastic bag might work better. Argon can be had from any welders' suppply outlet, and a tankful costs about $20... but you need a constant-flow regulator. These cost about $70 new. And there's a rental charge if you don't buy your own metal tank. But man, it's worth it.
 

Years ago I was living with roommates, and while working in the kitchen I noticed that the fluorescent light over the sink was about 8 inches long. A light went on in my brain ;) because I'd always wondered what would happen if a fluorescent tube was placed in a microwave oven. In theory the standing-wave RF energy should have enough voltage to ignite the mercury vapor into a plasma, and the lamp should light. But standard ovens put out at least 500 watts, so the tiny fluorescent tube should light quite brightly, to say the least. I'd never before encountered a fluorescent tube which was short enough to fit in an oven. So, I pulled out the tube, stuck it in the oven, said "THEY'RE HEEEEEERE!" , and punched the ON switch. Sure enough, the kitchen was lit up by a blue-white blaze of light coming from the front of the microwave oven. I only let it run for about 1 second, but this was enough to heat the fluorescent tube so it was too hot to touch.
 

(Yeah yeah yeah, I know I'm reeeeeally old, and most young whippersnappers never saw all those ads for the movie "Poltergeist," where the young daughter looks at the screen of the misbehaving TV set and says "they're here." )
 

Candle spews "Ball Lightnings"

In the late 1990s, someone on the Cold Fusion research forum mentioned a rumor: that if you cook a lit candle in your microwave oven, it will emit large buzzing gouts of plasma which will crawl around on the upper surface inside the oven. Yowza! So a large number of people tried this... without success. Only one person saw it happen, but nobody else could duplicate it.
 

Finally someone on another forum discovered the secret: high oven power, and carbon impurities! If your microwave oven can put out significantly more than 500 watts, and if you stick a bunch of charred toothpick fragments in the top of a lit candle... then sure enough, the candle will intermittently spit out orange "flames" made of plasma. The plasma rises immediately to the top of the oven and crawls around. When it winks out, the candle will emit another one.
 

Over many months, several people discovered easier ways to trigger the production of these "microwave plasmoids," including using graphite rods from mechanical pencils, or even using a lit cigarette. Check out the various links.
 

Cuppa burning plasma

Electric arcs can develop inside a microwave. The strength of the e-field inside the oven chamber can be described as "high voltage." Once a high-volt electric arc has been triggered, it will absorb energy from the microwave field. Sometimes it can break loose and fly around the oven like a "ball lightning." One way to trigger this effect is described above: place a lit candle inside the oven. Use a wide and stubby "votive candle" and stick some short pieces of charred toothpick into the top of the candle to supply some "seeds" of carbon (or ions?) for initial arc attachment.
 

A wandering electric arc can be captured in an upside-down container, J.L Naudin has some GIFs of this effect on his site. I tried it with a Pyrex measuring cup and it works! The cup became quite hot after only a few seconds of contact with the "plasma", so perhaps you shouldn't run it for very long. Or, if you have an old oven that you don't mind destroying, find out what happens when you run it for many minutes. Maybe you can melt the cup into incandescent glass-lava. [NEW: after about 30 seconds the cup goes "snap" and falls apart into shards. Apparently the plasma is as hot as a blow torch, and it shatters the glass.]
 

I supported the inverted cup-measure on three small paper cups. My candle was about 1in tall and 1in wide. I stuck several pieces of charred toothpicks into the top, lit the candle, then placed it below the glass container and shut the door.
 

The oven ran for a short time before the candle flame began creating eruptions of plasma. (If yours doesn't work, move the candle to another spot in order to locate a "hotspot.") Some of the plasma flickers blew away because of the oven fan and were lost, but finally one rose into the glass mug. The "plasma pool" fills half the cup and makes a loud 120Hz buzzing noise. It initially is dull orange, but then it changes color to pinkish blue. This color resembles the color of a glassblower's torch when borosilicate glass is being heated. Berhaps it's boron emission lines, or perhaps the color is associated with nitrogen/oxygen emission.
 

While working on a microwave article for an encyclopedia decades ago, it crossed my mind that it might be possible to map the pattern of RF energy in the oven by filling it with low pressure gas. The gas would glow in proportion to the RF electric field in various parts of the oven's volume. (There are better ways to do this, some below.) This would be an involved bit of construction to pull off, so I did the next best thing. I grabbed a big bag of NE-2 neon pilot lights and stuck them into a wineglass, hoping that this small volume would show some patterns when the glass was rotated by the oven's turntable. I filled the glass with water, to give the oven something to heat so it wouldn't be damaged by the small load presented by the bulbs. I ran the oven, and the bulbs glowed REALLY BRIGHT. As the turntable turned, various bulbs extinguished and others lit up. However, I could see no coherent patterns. When I emptied the glass, I discovered that several of the bulbs were stuck together. The short metal leads of some bulbs had melted into the glass of adjacent ones. Also, several of the bulbs had small holes melted through their glass, and were full of water. Apparently the plasma temperature was so high that it heated the glass to melting. Or, possibly some corona discharges developed between the inside and outside of the bulbs and burned through the glass. Hot glass is conductive, so the arc would continue once started.
 

Foil-eating Plasma

I'd seen electrical flames produced by microwave ovens before. In the strong RF field, even the tiniest flame will absorb a large percent of the many-hundred-watts oven output and grow large. Thousand watt candle? So, I decided to try initiating an electrical flame-discharge intentionally. I tore aluminum foil into 2" squares, crumpled it lightly so it didn't lay flat, then placed it on the oven turntable with the two foil pieces adjacent to each other and in gentle contact. Sure enough, when the oven was turned on there was a loud buzz and a bright light, and a flame erupted from the contact point between the two pieces of foil. When I looked in on them, I found that the brief flame had eaten a bite about the size of a dime out of both pieces.
 

Note: on some ovens the air from the fan will blow the foil around. DON'T SEAL UP THE FAN OUTLET!!! Instead, tape the foil down to the glass turntable. The air from the fan is hot because that fan is being used to cool the magnetron tube. If you block up the fan, the microwave generator will have a meltdown!
 

Miscellaneous Light Bulb in the Microwave

My 8" fluorescent tube isn't the only light producer. Another classic u-oven experiment is to cook a standard incandescent bulb briefly on "high". A 100W bulb will light up with more than normal brightness.
 

If you have a newer oven with rating over 800W, include a glass of water in the oven, otherwise the filament support wires will instantly melt and spoil your fun. Even with the water, don't run this for very long, since ALL the lightbulb wires glow white hot, not just the filament. This could shatter the bulb. For best results, buy a transparent bulb rather than a frosted bulb, then watch what happens inside. If you include a glass of water, the bulb makes purple discharges. If you DON'T include water, the bulb makes many colors as the metal wires melt or turn into incandescing vapor. I've had the glass of bulbs be melted and burst *outwards.* Apparently the pressure in the bulb rapidly becomes higher than atmospheric pressure.
 

There is an interesting bit of physics here: first the filament and its supporting wires glow white hot, but then they cool again. Bright blue beams leap from the tips of the filament supports and extend outwards to the glass, with bright "stars" of incandescence at the tips of the wires (many watts of Saint Elmo's Fire, like Nikola Tesla's 'carbon button' lamps!) This is a plasma discharge in the argon/nitrogen gas that is found inside all standard light bulbs. It's similar to Plasma Globe devices such as "eye of the storm", but 500 watts worth, which heats the glass red hot, and may melt the tips of the steel filament supports, or soften the glass so it is crushed by external air pressure! Another one: elgersmad suggests trying xenon flash tubes.
 

Note that most of these objects become intensely hot, so don't prop them up on a plastic object. And as usual, if this damages the microwave generator in your oven, don't come whining to ME! You know the risks, or you wouldn't be messing with this stuff. Go buy a huge old microwave oven for $5 at a garage sale, experiment with THAT.) Better check for door-leaks first!
 

Mapping the Energy Nodes

Microwave ovens cook unevenly because a pattern of standing waves forms inside the oven chamber, and the pattern creates an array of hotspots throughout the oven's volume. An operating frequency of around 2000 MHZ will produce a wavelength of around 10cm, and the hotspots should be at halfwave points, or every 5cm, but in a complex 3D pattern. I'd always wondered how this could be visualized. Perhaps fill the entire oven with raw eggwhites, then let the oven cook them into an interesting, white, rubbery 3D sculpture? Or fill the oven with solid wax, and let the RF hotspots melt out a 3D structure of holes? Finally someone figured it out:

Alistair Steyn-Ross and Alister Riddell, STANDING WAVES IN A MICROWAVE OVEN, The Physics Teacher, October 1990, Vol. 28 No. 7 pp474-476

Steyn-Ross and Riddell were stimulated to investigate the pattern of melted cheese on a "mu-oven" cooked pizza. They hit on the use of Cobalt Chloride soaked paper. When wet, CoCl solution is pink, but turns sky- blue when dry. (It's sometimes sold as "weather indicator" paper.) They discovered that this worked beautifully, and a large square of the paper would give varying patterns of pink and blue when supported at different heights on a tile of cork within the oven. The pattern is temporary, and disappears as the paper dries entirely. Also, cobalt chloride is poisonous, and should not be used around young kids.
 

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Danger: Coffee Explosion

You warm up a mug of water for a few minutes in the microwave oven. You take it out, then you dump in some powdered coffee, tea, sugar, etc...
 

DOOSH! The water explodes in roiling foam, spraying boiling water all over your bare skin, and sending you to the emergency ward. I hate it when that happens.
 

Heating up water or coffee in a microwave oven can be dangerous, especially if you use a ceramic mug or clean glassware. Water sometimes "explodes" because the oven heats it to a temperature that's far hotter than the normal boiling point. When this occurs, any tiny disturbance can trigger some violent boiling. The stored energy of the above-100C water is released as a steam explosion. This DOESN'T happen when water is boiled in a pot on the stove. The difference: a stove creates small hotspots on the bottom of the pot which are far above 100C degrees, and these hotspots continuously trigger a roiling boil which cools the rest of the water down to 100C.
 

Whenever there are bubbles of steam zipping up through the water, those bubbles provide some surfaces which allow the water to make more steam, and as steam is created, the water cools down to 100C. In fact, water can only "boil" at places where the water surface touches a gas. If there are no bubbles already formed, then "boiling" will only happen at the top surface of the water and not down within it. So, whenever you heat water on the stove, the extreme temperature at the bottom of the pot causes tiny bubbles to form. The boiling water fills those bubbles with steam. The roiling bubbles act to cool the water and keep its temperature at (or below) 100C/212F degrees.
 

Things are different in a microwave oven. The water gets hot but the container usually does not. There are no tiny "boiling-bubbles" triggered by a hot stove burner. Without those bubbles to cool it, the temperature of the water can rise far higher than 100C. We call this "superheated water."
 

Superheated water is just waiting for some sort of trigger which will let bubbles form and allow boiling to commence. If the water becomes hot enough, a few bubbles will appear near the top, but these quickly rise and burst, and the water isn't cooled much at all. Even if your mug of water is bubbling slightly, don't trust it, since its temperature has risen so high above 100C that bubbles are appearing spontaneously. If some unwitting victim should pour powder into the superheated water, this will carry thousands of tiny air bubbles into the water. Each of these micro-bubbles expands into a large steam bubble, and the result is a huge "explosion" of hot froth. It's just like dumping ice cream into rootbeer, but the froth can be so violent that the hot water sprays into the air.
 

Even more dangerous is to boil water TWICE in a microwave oven. Most containers have tiny scratches in their surfaces, and these crevices contain air. When you heat water, these tiny air pockets will provide a constant stream of "seed bubbles" which allow normal boiling to occur. However, the air in these tiny bubbles within the cracks quickly gets replaced by steam. The crevices still produce seed-bubbles, but if you turn off the oven and let the water cool, the steam in the cracks will collapse and vanish, and the crevices fill with water. The seed bubbles are gone. If you now turn the oven on again, the water will superheat. Boiling your coffee twice can erase the bubble "nucleation centers." If your luck is bad, the water will superheat to a very high temperature, then explode violently when a single huge steam bubble spontaneously appears. If that bubble should start out at the bottom of the container, the explosion can fling the entire volume of hot water upwards. A few people have reported that sometimes the explosion is so violent that it makes a sharp noise, and can even crack a glass container.
 

If you avoid the items on this list, you'll probably never see a "coffee explosion." On the other hand, the above list is a "recipe for disaster." DON'T BE TEMPTED TO FOLLOW IT. Instead, here's a simple, HAZARDOUS experiment to try. Wear safety goggles, and don't heat the water for an excessive amount of time.
 

Fill a clean mug about 1/3 full of clean water (DON'T FILL IT TO THE TOP!), then heat it for about five minutes in the microwave oven. Now carefully take it out and immediately plunk it firmly onto the tabletop (whack it hard, but not so hard that it breaks.) The boiling water will burst into froth. DON'T BURN YOURSELF! The superheated water acts almost like warm carbonated cola: if you strike the container, it will foam up instantly.
 

Another trick: heat up the water to boiling again, remove it from the oven, then immediately insert a dry wooden coffee-stirrer, or a wooden popcicle stick into the water. Foosh! The water boils violently. The dry wood contributes a layer of air to the water, and the air fills with steam and expands into a mass of hot foam.
 

Another: heat up the water again, then pour a little bit of warm tap water into the superheated water. The water suddenly boils violently! It turns out that the tap water is full of tiny bubbles. If you let the tap water stand around for half an hour before pouring it into the superheated water, all the tiny bubbles in the tap water will have risen and popped, and the bubble-free water won't trigger any violent boiling. And if you then dissolve some salt into your "bubble-free" tap water, again that water WILL trigger boiling, since the salt contributes invisibly small bubbles.
 

Hmmmm. I wonder if de-ionized distilled water in a REALLY CLEAN container will superheat even more than normal? (DANGER, SUPERHEATED WATER CAN BURST OUT OF THE MUG AND SCALD YOU!) I wonder what would happen if we used vacuum-degassed water, or if we put some dishwashing soap in the water...
 

SAFETY WARNING: Treat microwave-boiled water with respect. It can "explode" without warning. You can "defuse" it by CAREFULLY inserting a dry wooden stir-stick or toothpick in order to trigger boiling. Don't dump any sugar in a mug of superheated coffee, or the spewing foam *really* gets violent. Don't try to boil liquids more than once, since that removes the tiny bubbles on the container surfaces which act as boiling centers. If you're going to re-heat a previously heated mug of liquid, cook it with a wooden stir-stick or wood chopstick which allows it to boil normally. Always allow bubbling liquids to cool for several minutes before adding anything to them (or perhaps reach over and carefully drop in a dry toothpick or a wooden stir-stick to force them into normal boiling mode.)
 

PS
Certain types of foods have no bubbles inside, and these foods will superheat and "explode." For example, never cook a whole unbroken egg in a microwave oven. The explosion isn't just messy, sometimes it's violent enough to smash up the inside of your oven or tear off the door. Paste-like canned foods easily superheat since they're too thick to allow streams of tiny bubbles to form. Canned spaghetti sauce is famous for superheating and causing those "BOOMF" mini-explosions that spray the sauce all over the oven. (I wonder if there's any cure for the "Spaghetti-O explosions?" Maybe whip the stuff with a fork before cooking, so lots of air is added? Mix it with dry bread crumbs or other material that's full of air?)
 

• Flash-boiling experiment
• How things work: exploding coffee
• FDA: Erupted hot water phenomenon
• Superheating
• Superheating and microwave ovens

CLASSICS

There are many other excellent microwave demos on other sites. Stand up a CD in your oven and nuke it for about five seconds. Or convert Marshmallow Peeps into monsterous mutants. Slice a grape almost in half and watch it emit a six inch blowtorch of flaming plasma. Make showers of sparks with steel wool. Swell a chunk of Ivory soap into a blob of crunchy snow. Gamble on racing grapes.
 

Google microwave oven search on:

• CDROM
• Peeps
• Grape
• Steel wool
• Soap
• Grape racing

Untried experiments

Generate a glob of soot from burning paint thinner. Replace the air within the soot ball with pure oxygen, or ozone, or nitrogen, or argon. Place it within an active microwave oven. Is a Ball Lightning plasmoid created?
 

Light a candle and place it in the oven. Does the RF energy make the candle flame grow huge? If you place various metal salts on the wick, will the colored candle flame absorb RF energy better? Or, try running a wire up through the candle so its tip is in the flame. Any effects? There are reports of "ball lightning" being generated from candles, burning toothpicks, and burning plastic in Microwave Ovens.
 

Partially inflate a balloon with argon. Release the argon to purge the bit of air that was in the balloon, then fill it with pure argon. Carefully insert a wire up into the balloon so the wire tip is near the center of the sphere. Tie off the balloon. Place it on a plate in a microwave oven and turn it on. This should create a 700 watt "plasma ball" effect. However, it might also pop the balloon instantly. The tip of the wire will probably be melted by the intense corona. Anyone for "Kirlian photography" which vaporizes the object being photographed? If the balloon pops instantly, try the same thing by using a plexiglas box. (note: glue fumes wreck the effect, so hold the plexiglas together with tape.)
 

Microwave oven Ball Lightning

Ball Lightning triggers

• Jon's tricks, plus earliest mention of candle in uW
• Crowley: Bigger Better Balls
• C. Willis
• Neon HV transformer
• Naudin 1, and 2
•  
• Braniac Science Abuse: Microwave ovens (youtube)
• Microwave Phenomenon Page
• MW Oven Ball Lightning messages
• Ball Lightning page
• More Microwave BL
• Abstract: Golka1.html from Atmospheric Electricity Page
• Microwave oven BL, from Keelynet

Microwave oven chemistry experiments

• Experiment: use MW oven to make gases
• Microwave Oven Reaction Enhanced Chemistry
• Microwave chemistry
• Sintered metal parts
• Microwave oven dry chemistry
• ACS: MDD, "The nuke's the thing for synthesis"
• Make diamond powder in your kitchen?

Misc sites

• Microwave oven safety (fda.gov)
• "Microwave" on Google Video and Youtube
• Brainiac Science Abuse
• CDROM art
• Microwaved Peeps!
• One Hundred NE-2s in a microwave
• Hochwald safe/unsafe experiments
• Microwave oven as foundry furnace
• Ask a scientist: microwave ovens
• CD + MW oven + TESLA COIL!!
• CD Toasties
• Microwave oven lecture demo
• Funny things w/microwave
• Glubco, far more "unwise" than I!
• Fun with Grapes - A Case Study
• Grape Racing!
• T.W.I.N.K.I.E.S. Radiation Test
• Jon's microwave games
• CD-ROM's in the Microwave
• Microwave Oven Q & A at HOW THINGS WORK
• Microwave Oven FAQ at sci.electronics.repair
• Microwave Acoustics, w/refs on microwave hearing
• Microwave Oven info, FAQs, repair
• Microwave Ovens and Safety
• Microwave Oven
• Microwave Oven Radiation Leakage
• Microwave Furnace Development
• EEED Medical Technology
• SVBx Labs (archive.org)