I asked Matt Wilson from Echo Bridge Productions a couple of questions about the special effects techniques used in Willy Wonka and the Chocolate Factory.

I asked three questions:
1. Tell me about how they managed to float in the "Fizzy lifting drinks" scene.
2. How do they change Violets face in the famous "Blueberry" scene?
3. How did they shoot Augustus Gloop up that pipe?

Matt replied with lengthy explanations of the effects. Everything he had to say is posted below. Thank you tons for your all of your knowledge Matt!

I copied and pasted right from his e-mail... here it is:

The "Wonka" scene in the Fizzy Lifting Drinks room was created with
several effects techniques, many of the same techniques which were later
used in "Back to the Future II" for the hoverboard scene.

* Flying Harnesses
Many movies and even some stage plays require flying harnesses. The
centerpoint of gravity on a human is the hips, which is why football
players are taught to watch their opponent's movements at the hips.
(Another player can "feint" to one direction with his extremeties while he
is really going the other way. But the hips don't lie because that is where
balance is.) So, most flying harnesses are some kind of "shorts" with
gimballed connections on either side. An outer costume hides the harness.

With a little practice, a performer can learn to control his
orientation and do tumbles around his hip "axis." (Charlie does a tumble in
the drinks scene.) Of course, the actors must also do their best not to
"give away" the mechanism of the harness by bumping the wires, or allowing
their clothes to be pulled by some "unseen" force.

Video has a much lower resolution than film, but some video is
better than others. A wire harness may be visible on film, but the
"noisier" image on video could successfully hide it. If you are watching
"Wonka" on VHS, the wires may not be visible. I can see them on laserdisc.
In "Back to the Future II" some of the wire harnessing is visible, too.

There are ways to reduce the visibility of the wires. I've read of
one technique where the wires are scrubbed with an acid to reduce their
shine, but that weakens the wires somewhat. Sometimes darker wires, or
"painted" wires might be used, as in "Fantastic Voyage" for the SCUBA
scenes. Depending on the scene, it might be possible to reorient the set so
that wires are hidden, or come from another direction (so that you don't
know where to look for them). For "2001: A Space Odyssey" the set designers
built the emergency airlock and HAL's brain complex vertically so that the
camera pointed up. The actor was then lowered toward the camera, hiding his
own wires, so that he appeared to be in "zero G."

*Wire Removal
Using a computer, there is another technique nowadays called "wire
removal" where wires or other supports can be erased, frame-by-frame. If
you have ever played with Adobe Photoshop, the rubberstamp tool is one
approach you might use. With this digital technique wires and supports can
be large enough for safety because they can always be rubbed out.

*Travelling Mattes
Charlie and Grandpa Joe where also bluescreened into one shot
looking straight up the bubble tower. Bluescreening is only one method of
creating "travelling mattes," which is a technique for cutting and pasting
moving images together. The actors merely stood in front of the screen and
flapped like birds. They were later optically "cut out" and pasted into the
tower background. Bubbles were also added optically to give the shot depth.

*Sleight of Hand
For the shots near the top of the tower, close to the ventilator
fan, the actors stood on moveable platforms like the cherry-picker of an
electrical truck. Since their feet were not in the shot, they could be
"craned" up and down from below camera view.

*Blueberries
Denise Nickerson wore two different costumes for Violet
Beauregarde's blueberry scene. One costume started "normal" and was
inflated by an off-camera compressor, and the other costume was designed to
be fully round with no hoses attached. The biggest reason for the two
costumes is because the human shape does not easily "morph" into a round
ball--the arms are too long, for one thing. The starting costume cleverly
used pleats to hide the extra material, and a belt to bunch it together.

Ms. Nickerson's face was turned blue with an optical effect at
first, and make-up later on. A blue light might be one approach, but it
would have problems. Any other white light in the area would tend to
override the darker blue light. Also, blue lights would have to be used on
the "key" (brighter) side of her head, as well as the "fill" (darker) side
of her head. There is also the problem of other actors possibly stepping
into the blue light. For example, Mr. Beauregarde steps "behind" Violet
relative to the camera. That and other things make me doubtful that blue
lights were used.

The travelling matte technique mentioned above was most likely used
to turn Violet blue. Like the lightsabers in "Star Wars" or the blue eyes
in "Dune," an artist sits down and traces the area to be affected,
frame-by-frame. These "mattes" are then animated onto new film like a
cartoon. That travelling matte is then used to make a blue exposure onto
Violet's face (kind of a "double exposure").

Because an imperfect human is involved in the process, a hand-drawn
travelling matte (a.k.a. "rotoscope") may often have a "buzzing" edge to it
where the artist traced a little high one time, and a little low on another
frame, etc. To reduce that problem the optical technicians for "Wonka"
soft-focussed the mattes for Violet's face, thus bleeding some of the blue
across her hair (and even the suit, which was already blue). The bleed to
her hair was necessary since a little bit of fleshtone is visible at the
part in one's hair. Depending on your copy of "Wonka" you may be able to
see the exact frame when the blue mattes were "turned on." The dissolve was
not perfect, and you can see a little bit of an optical "pop" as the color
is added (the dissolve was not smooth).

Another telltale is the reverse shot with Violet looking away from
the camera towards her companions. Watch the lower part of her cheek and
you will see some of that matteline "buzzing" I mentioned. With computer
techniques today a perfect matte could be generated so exacting that it
could fit around even the finest hairs. There was a TV commercial, about a
year or two ago, which used this technique to advertize a blueberry
flavored breakfast cereal. (As the speaker turns blue it looks as if some
invisible person scribbled across his face with a blue crayon.)

For the sake of timing, make-up was not applied to Nickerson's face
until the round costume was used, as you noted. No make-up is perfect, and
starkly non-fleshtone colors (like blue) have the problem of eyes and mouth
to contend with. Make-up cannot be applied too closely to these areas, so a
red rim around the eyes, and of course the pink of gums and any uncovered
lips is very apparent. For that reason, and maybe also in an attempt to
match the two blue shades, some of the "round" shots were further enhanced
with the travelling matte technique mentioned above.

If you look at the attached image (from the non-letterboxed
"Wonka"), you will note that the blue of Nickerson's face and that of her
hands does not match. Her hands must be the original color of the make-up.
The shine you spoke of is another give away that make-up was used. This
does not mean that the make-up was necessarily shiny. Someone with light
skin gives off light more evenly, while someone with darker skin has a more
pronounced gradient from light to dark. That is, highlights are more
noticeable. This is just one more telltale in the beginning shots that
Nickerson was still fleshtoned as they shot the scene. The computer
enhanced commercial I mentioned above accounted for this, too, creating a
"perfect" effect.

So, you can imagine how difficult Violet's scenes must be for a
stage production, and what sorts of compromises must be made to pull it off.

"high speed film" is exactly the way that the filmmakers of "Willy
Wonka" shot Augustus Gloop up the pipe. Special FX and stunts often tread
the same ground. And performer safety should always be foremost. Any FX man
who seriously injures an actor is not likely to work in the field again.
(If he's even lucky enough to avoid damaging legal repercussions.)

Special FX are used to capture on film anything which is 1) too
expensive to do in "real life"; 2) too dangerous to do in "real life"/full
scale; 3) things which are otherwise impossible (like people turning into
blueberries) or do not yet exist (giant, alien space cities). Today, you
might want to throw in a fourth reason for special FX--audiences love it
and it makes big bucks.

But back to Augustus. The "chocolate" was, of course, water doped
to look brown. Part of the illusion with this effect is the assumption that
the lucite pipe is open-ended at the bottom. If you know how a barometer
works, you'll realize why that would be impossible. So, the pipe was sealed
at the bottom and the actor was lowered into the tube. For close-ups the
pipe was probably sectioned so that it was not necessary to subject the
actor to the claustrophobic experience of being lowered down such a long
pipe.

For the long shots the actor would be suspended by wires while
"chocolate" water was pumped into the tube to the proper height to make it
look as if it were holding him up. (You will also note how the filmmakers
arranged for one of the pipe joints to be right at the level of the water.
This way it never occurs to the viewer that Augustus' stomach is not really
plugging the pipe. If water made it past his waist and up to his shoulders,
it would be spraying like a garden hose.)

Lastly, note the "shimmering" of the chocolate river as Augustus
goes up the pipe--the film is definitely "sped up" (known as frame
clipping). Other tell-tale indicators are that Augustus' image does not
blur as he shoots up the pipe. That sort of staccato motion (called
"pixelation") is what often "gives away" stop-motion effects. The animators
for "The Empire Strikes Back" developed a system called "Go-Motion" to
eliminate that problem. The blurring of the Tauntaun's legs as it runs
makes the shot look that much more credible.

Safety issues come up in some of the other FX for "Wonka." The
ventilator fan in the Fizzy Lifting drinks room probably had a glass plate
in front of it. Although the fan was probably made out of lightweight
materials, the actor could still get a nasty sprain if his hand
accidentally missed the fan strut and plunged into the "blades."

(In "Raiders of the Lost Ark" there is a shot in the "Well of
Souls" scene where Indy falls to the ground and lands face-to-face with a
cobra. Although the snake was most likely devenomed, it might still strike
at a moving actor. Look carefully at the ground and you will see the
division in the sand where the filmmakers placed the window that separated
Harrison Ford and the snake.)

A magician is not supposed to tell his secrets, but I find that in
studying special FX I gain a greater appreciation for the filmmaker's art.
(Sound design and foley work are often an overlooked, but truly fascinating
aspect of a movie's artificial reality.)