The "Tesla Coil" of the 1990s
UNWISE MICROWAVE OVEN EXPERIMENTS
High Voltage in the Kitchen

Microwave Magma: a lava flow of liquid Pyrex

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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 resistor? 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 trees. 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 find 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." (remove glass rotor dish; needs a totally empty oven.) The tiny red glow will increase wildly. Just remember to shut it down before the advancing "lava flow" pours down 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 ...Unwise.

"LAVA" CHAMBER:
I found a hunk of porus red rock used as "decorative stone" under some shrubbery. I'm told that it's probably slag from the iron industry. Would the stuff turn conductive when hot? Lets find out! I put it on a small overturned flower pot in the oven, then heated a small spot to orange heat, then slammed the door and started it up. The orange heat died away. It seemingly went dead. But then my intuition kicked in: wouldn't the surface radiate away the energy, while deeper within, the material was still absorbing microwaves like crazy? The hot region... should MIGRATE! It should move into the center of the rock where plenty of RF is heating it, but where it's surrounded with nice insulating, non-microwave-absorbing rock. Let's let it cook and see what happens. Hmmm. Inside the pores in the rock I see something red. Now it's yellow. Now there's a crevice. The whole side of the small rock splits open, collapses, revealing the interior of a white hot miniature magma chamber. An orange river of magma pours forth! I stop the oven, and the flow halts before it gets to the bottom. Through the open door I can feel the radiating heat on my face. Hope it doesn't set the painted metal walls on fire!

REAL MAGMA:
Next I triggered some heating in a small piece of obsidian. I hoped to re-liquify some actual lava, rather than melting the manmade materials above. But I didn't remember an important fact: Hawaiian volcanos slurp outwards, but magma from American volcanos is more like a white hot jet engine filled with powdered glass... because American lava is full of dissolved gas. Sure enough, the black obsidian melted in the microwave oven. Sure enough, it expanded into a large white puff of glass foam, sort of like a popped popcorn kernel.

BEER BOTTLE:
Find a bottle that's short enough to stand upright in the oven. I recommend "Red Stripe" Jamaican ale. (Grin.) Yes, with care you can heat a spot on the glass bottle to dull red heat but without shattering the bottle. And yes, the microwave output of your oven will then raise it to incandescent white hot, melting a hole right through which grows larger and larger. And yes, during cooling the bottle will shatter, launching hot fragments all over the kitchen. Keep the oven door closed. If the bottle doesn't break, wear gloves and whack it with a screwdriver while the door is almost shut.

Also see on Usenet:

[Dec 2003] Molten lava in your microwave

[Nov 2003] I just melted a frikkn beer bottle!

LIGHTNING STORM

Hobbyists discovered the joys of high voltage Argon a few years ago. Shoot foot-long lighting bolts from your bare 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 "inverted pool o' plasma" 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. Very acrid if sniffed, so probably various oxides of nitrogen.

So next, I put a half-liter of argon in a white kitchen trash bag, threw in a piece of carbon fiber, then squeezed out all the argon (to flush any remaining nitrogen totally out.) Then I filled about 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 and ignited.
• 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 through white kitchen trash bags, although a clear plastic bag works slightly 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.

(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

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.

NEW EXPERIMENT:
I used honey to adhere some salt (NaCl) to the inner surface of the pyrex cup in hopes that I'd see some yellow Sodium light. This works well. At first the captured plasma blob turned pinkish blue, but then a wave of brilliant yellow/orange light passed through it. This effect repeated several times, and I suspect that salt crystals are falling off the glass surface and passing through the plasma, releasing sodium ions as they go. Other salts to try: salt replacement (potassium chloride), copper sulfate, borax, epsom salts, perhaps even strontium chloride for red color. Search for info about fireworks colorants.

IMPROVEMENT:
See Matt Crowley's paper on Bigger Better Balls

LESS WISE EXPERIMENT:
Years ago there was a news story about a new kind of efficient light source: a quartz capsule of sulfur which was blasted with microwaves. What will happen if the above salt crystals are replaced with powdered sulfur? Blasts of intense white light? I haven't tried it yet. [NOW I DID! No brilliant light. Instead, the plasma forms, then the sulfur reacts with air to create a cloud of acrid gas. Sulfuric acid?!! Suddenly I find that I can't breathe the air in my kitchen. Hold nose, turn on the fans, and leave the house at a run!]

To try next: put a tiny hole in the upside-down glass cup (or perhaps use a chemist's funnel.) Will the pool of plasma drain out upwards through the hole? Or will the oven keep making more plasma as bits leak out? If I had a ceramic tube, could I guide the plasma through a hole and outside the oven? Home-built plasma torch!!

Snifter of Neon

Foil-eating Plasma

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

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

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

More recently, J. E. Slone of Virginia tells me that thermal FAX paper can be used for the same thing if is is slightly moistened. When placed on an insulating plate within the microwave oven, the hotspots heat the water to boiling which creates a permanent image of the standing wave pattern. Kool! Both of the above experiments will only work if your oven lacks a "stirrer," a fan which wiggles the hotspots and spreads them out. If your oven has a rotating turntable, it usually lacks a stirrer.

Danger: Coffee Explosion

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.

MOST DANGEROUS:   - BOILING PLAIN WATER...   - IN A CLEAN SHINY CONTAINER (MUG OR PYREX)...   - BOILING IT MORE THAN ONCE (LET IT COOL BETWEEN BOILINGS)...   - COOKING IT EXTRA LONG (STORES LOTS OF ENERGY IN SUPERHEATING)...   - REMOVING IT IMMEDIATELY (NO CHANCE TO COOL DOWN)   - DUMPING IN SUGAR, CREAMER, A TEABAG, ETC. (SUDDENLY ADDS SEED BUBBLES)

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?)

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

CLASSICS

Google microwave oven search on:

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

Untried experiments

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.)

Try the infamous Microwave Powered Water-Fueled Lawn Mower. Do huge pulses of EM really extract energy from a mysterious source within water? Dr. Graneau says that high current discharge through liquid water produces numerous anomalies. Laugh if you wish, but only the real world can supply the real answer. "Let the experiment be Made!"

MICROWAVE OVEN MYTHS

ALSO: More and weirder non-microwave experiments

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
• Bottle Melt BBC Bang goes the Theory
• YT playlist, microwave bottle-melting
• Bottle explosion lethal danger
• 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 cooktop (NOT oven!)
• Oven physics: Q-factor of 10,000 for steel oven (.pdf)
• "Microwave" on 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)