

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 microwave wattage then attacked the glass. Yet glass is mostly transparent to microwaves, so it shouldn't heat up. WTF?!!



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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 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 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.

They're Heeeeere! 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.

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 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.

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.

