Skins of air which float around underwater,
and vanish when touched!
1997 William J. Beaty
Everyone is familiar with bubbles! There are three basic types:
Pockets of air under water
Air trapped under a water film
Bubbles which float in the air
Besides the above bubbles, there are three other kinds which are not as
familiar. These are the ANTIBUBBLES. An Antibubble is similar to a
bubble, but the roles of the water and the air are reversed.
The first type of antibubble is familiar. it is simply a drop of water
falling through the air. It is the opposite of an underwater bubble:
rather than being a blob of air in the water, it is a blob of water in the
Fig. 4 Falling droplet of water
When a drop of water falls into water, we expect it to vanish. But
sometimes it does not. If the water is very clean, then a thin skin of
air will become trapped between the water droplet and the rest of the
water. This effect is sometimes called a "Water Globule" or "floating
drops." If you've spent any time sitting in a car on a rainy day, you
will have seen water globules skittering across the hood. When raindrops
splash on the car hood, you'll see the splashing droplets roll across the
wet surface without melding into the rest of the water.
Fig. 5 "Water Globule" on the surface
A water globule is the opposite of an air bubble on the surface of water.
Rather than being a pocket of air with a thin skin of water separating it
from the air, it is a blob of water with a thin skin of air separating it
from the water.
The last type of Antibubble is usually called by the name...
"Antibubble." It is a very thin skin of air which floats around under the
water. Antibubbles don't form easily, and they usually pop quickly, so
most people have never seen them. However, it is possible with a little
practice to create them yourself.
Fig. 6 "Antibubble" floats underwater
Antibubbles have many of the characteristics of soap bubbles. They float
underwater weightlessly, and will only rise to the surface of the water
very slowly. When poked, they will pop. When a soap bubble pops it
leaves behind a tiny drop of water, but when an antibubble pops it leaves
behind a tiny normal bubble. Antibubbles also display rainbow colors.
Normal soap bubbles have rings of color at the top of the bubble where the
soap film is thinnest, while antibubbles have their colors at their
BLOW YOUR OWN UNDERWATER ANTIBUBBLES
The key to creating antibubbles is to make a very clean water surface.
The tiniest bit of surface dirt will prevent antibubbles from forming, or
will make them quickly pop. To create a clean surface, allow a container
of water to continuously overflow . The overflow causes the surface of
the water to stretch and be pulled sideways, and any dirt on the water
surface will be skimmed off. Fill your large jar, place it in the sink,
and adjust your faucet to allow a continuous stream of water to pour in
and overflow the jar.
- Kitchen sink
- Large clean jar
- Elmer's (tm) glue bottle, emptied and cleaned
- Dishwashing detergent
Fig. 7 Constant overflow cleans the surface
Add some soap to the jar of water and stir well. Fill your glue bottle
with soapy water from the jar.
To get familiar with how antibubbles behave, first try making some
"globules." Spray some droplets up from below, so the droplets land on
the surface of the water. If you can build up lots of globules, you'll
see them bounce off each other, or "pop" and join the rest of the water.
Sometimes they'll join together into larger and larger ones.
Fig. 8 Squirt some globules onto the water
You can demonstrate that the thin film of air is disrupted by
electrostatic forces. Comb your hair to give the comb an electric charge
imbalance. Spray some globules on the surface of the water, then wave the
charged comb near them. They will abruptly vanish! They all "pop" and
rejoin the water. The electrified comb causes the water in the globule to
split into areas of positive and negative charge. This imbalanced charge
attracts the water below the globule, and the globule crashes into the
water below. On a dry day, your body can become electrified from walking
on the floor, and this can disrupt antibubbles and globules. If your
globules and antibubbles refuse to form, try touching the metal faucet to
remove any charge imbalance from yourself. "Static electric" page
OK, let's make some real antibubbles. Follow the three steps below.
First place the tip of your water-filled squirt bottle very near the water
Give it a gentle puff and create a single water globule. Immediately give
a longer squeeze. This will send a jet of water through the globule and
down into the jar. If your squeeze is gentle and brief, the water jet
will take the air layer along. A long silvery worm will extend into the
water. This "worm" is water which is coated with air. Do this several
times, and sometimes the worm will break up into antibubbles of different
Fig. 9 Make a globule.
Fig. 10 Squirt through the globule.
Fig. 11 Watch for antibubbles!
Your first underwater antibubbles will probably be small, under 1/8 inch
across. With practice it is possible to blow 1/4" antibubbles, and
occasionally 1/2" antibubbles.
To prove that this is no ordinary bubble, poke it with a pencil or fork.
It will instantly vanish.
Antibubbles will slowly rise to the surface, where they will often pop.
To extend their life time, stick the bottle tip in the water and squirt at
them to drive them deeper into the jar. Vibration is supposed to extend
their lifetimes, so squirting them with underwater jets may keep them
alive longer. Temperature difference is also said to lengthen their
lifetimes. Try filling your glue bottle with hot water, while putting
cold water in your overflowing jar.
Antibubbles display rings of color, but these colors appear at the bottom
of the bubbles rather than at the top. Look closely at your antibubbles
under bright light, and you'll see that each one has "soap film colors."
But in this case we should call them "air film colors." The color of soap
films (and of oil on water) are caused by light reflections from a very
thin, transparent layer. Light reflects from the front of the thin layer
and from the back. If the layer is almost as thin as light waves, the
certain colors of light waves from the two reflections cancel out,
producing a "subtractive rainbow" with cyan/magenta/yellow instead of
red/green/blue. In a normal bubble the thin water layer creates the
colors. In an antibubble, the colors are created by the thin layer of
Conventional bubbles can be filled with cigarette smoke, and they release
a little cloud when they pop. Antibubbles can also be filled with colors.
Just put some food coloring in your squirt bottle. If several kids have
squirt bottles with differing colors of water, everyone can keep track of
their own antibubbles in the same jar.
To demonstrate all the various bubbles (antibubbles, bubbles, globules,
antibubbles inside bubbles, anti-foams, etc.) make yourself an oil/alcohol
bottle. Clean out a small jar and fill it half with salad oil, then fill
the rest with rubbing alcohol. Try to fill it perfectly, right up to the
top, so no air is trapped. Screw on the cap, then slosh it gently to
create waves, or a bit harder to create all sorts of bubbles-within-
bubbles. (Don't shake it hard, or it will take hours for the misty
mixture to settle out.)
For more information about all of this, find a local library with back
issues of Scientific American magazine. ( Or, order them through your
library's Interlibrary Loan.) The "Amateur Scientist" columns for April
1974 and for August 1976 discuss antibubbles. On WWW, search for keyword
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