Two and a half years ago I wrote about the science of Mr. Freeze´s freezing gun with reference to the 1997 epic (flop) Batman and Robin. This small blog is still generating views and is the most visited thing on my site that I’ve ever written. But why is that? What is it about the freezing ray that is so fascinating to the average geek? (I really want to say “because it’s cool” but then I’d have to punch myself in the face.)

This film frequently makes it onto top 10 lists of the worst movies ever made but even so, there are still people like me that absolutely love it. Corny? Yes. Bad acting? Yes. Terrible representation of beloved DC characters? Yes. But it is still enjoyable as hell (…IMO).

But there is another aspect of the film (that I personally love) which doesn’t get as much credit as it should; the way it looks. There are a lot of cool (sigh… yeah sure, pun intended) set designs, Mr. Freeze´s gun looks great and many of visual effects are exceedingly well done. Not only is science behind a freezing ray interesting and a bit intimidating but the gun itself looks pretty bad-ass.

It does look like a lot of work and effort was put into the development, design and construction of the gun prop that is used in the film. It seems to trigger some sort of light upon the pressing of a button and when it is fired there are flashing lights that you can see reflected in the actors´ faces.

Now, here´s when things get knocked into twelfth gear…

Recently, the designer of the gun apparently read my blog about the science of the freezing gun and contacted me. (Life is crazy sometimes.) He offered to send me pictures of some of the gadgets and indulge me with how everything worked which included a lot of technical coordination between the gun and the cameras. Only as long as he could keep his anonymity.

Needless to say, I was ecstatic to get the opportunity to know more about the intricate workings of the Freeze Gun and it inspired me to write a little bit about it. In the end I wanted to ensure everything here is technically correct (the best kind of correct) so at times this got to be a bit… technical.

In the following I will go into the science and design of the actual freezing gun that was used on set. For the time being, when needed, I will whimsically refer to him as Mr. E (wrong movie, right franchise, tihihi).

Let’s focus on the gun itself first.

The Freeze Gun design

The gun’s body was made of a type of fiberglass which is very durable and simultaneously flexible. The body is covered in a reflective finish that is produced via a process called “flash metallization” where plastic objects can be made to look like polished metal. Faux diamonds were attached to the power source, hiding much of the gun’s inner electronics. A small switch on the left side of the gun operates the body of the weapon, and the electronics were powered with a single rechargeable cordless drill battery. Small radio antennae protrude from each side of the gun which were related to a small row of switches hidden inside the battery compartment. The one on the right acted as a receiver and on the left as a transmitter which ensured that the gun had wireless data input and output.

(pictures link: https://propstoreauction.com/view-auctions/catalog/id/78/lot/18140 )

Its dimensions were approx. 99 cm x 18 cm x 36 cm (39‘‘ x 7‘‘ x 14‘‘).

The barrel of the gun contains a series of helical strobe lights that needed to be coordinated with the cameras and external strobe lights to provide additional lighting effects. This requires a bit of science.

Strobe Ligths

Strobes, or stroboscopic lamps, emit regular flashes of light. These discharges of light can be emitted in a time as short as a few milliseconds and since recording cameras operate by taking thousands of stills and playing them in sequence, it is important that these discharges of light and the cameras are synchronized. More on that later.

The scientific principles behind the operation of strobe lights are pretty nifty. In short, a sealed glass tube (the ones in the gun are helical) which contains a nonreactive noble gas (in the case of the Freeze Gun, Xenon), is placed between two capacitors at opposite ends of the glass tube. When the capacitors are supplied with a voltage power source, an electric arc is produced where energetic electrons are catapulted from one capacitor to the other. The electrons clash with the Xenon atoms inside the glass tubes and part of the electrons’ kinetic energy is transferred to the Xenon atoms who (i) become electrically excited by the impact or (ii) are ionized where they lose an electron and form a positively charged Xe⁺ ion (which can easily recombine with the slurry of electrons available to again form a neutral Xe atom). When atoms become electrically excited in this way, they opt to relax and give their excess energy away in the form of a photon. I.e. to continually relieve themselves of all this energy they are obtaining from the stream of electrons, they emit photons and cause the glass tube to light up.

A classic picture of atomic excitation and emission. Within the strobe light paradigm, the energy required to excite the atoms is acquired by energetic electrons that collide with the atom rather than another photon as pictured above. The emission of the photon in the strobe tube is, however, governed by the same dynamics as displayed on the right.

The photon production is an extremely efficient way for atoms to relax their energies and find a more suitable, less-excited state. Not only are photons produced when a single atom jumps from a high energy state to a low one, but it is also the preferred method of relaxation during collisions between ions and neutral atoms where an electron is transported from the neutral atom to the ion. The collision itself may cause additional energies to be exchanged between the ion and neutral and hence, producing a photon is a preferred mechanism of the atom to release excess energy.

The color of the strobe light finally reflects the distribution of the energies of the produced photons. Of all the noble gases, Xenon´s flashtube spectrum is the one that comes closest to white light, but it does appear distinctively blueish. Comparatively, Neon’s spectrum is more reddish.

The figure above shows the per wavelength irradiance for the noble gases Xenon, Krypton, Argon and Neon, when placed in a flashtube. In layman’s terms it is a scale for how many photons are produced at particular wavelengths of light. Neon’s flashtube spectrum appears red because most of its irradiance falls between 0.6 and 0.7 microns (one millionth of a meter), which is the red portion of the visible electromagnetic spectrum (see figure below). Comparably, Xenon (which gives off a more whitish light) while it’s maximum irradiance is between 0.45 and 0.55 microns, which is the blue portion of the visible spectrum. However, since Xenon emits a considerable amount of photons over the entire visible spectrum, the light appears more white with a tint of blue.

The differences in color of a Xenon flash lamp (left) and a Neon flash lamp (right). (Neon is not more rude than other noble gases, some people just like to make it look that way.)

Let’s get back to the Freeze Gun.

There were four strobe tubes wrapped a quarter of the way around the ~1.5´´ diameter inner Lexan barrel. (Lexan is the brand name for a polycarbonate resin {plastics made from a repeating sequence of molecular structures that contain a carbonate group; –O–(C=O)–O–}.) They were wrapped 360° around the barrel over a length of about 6 inches. Each segment was about 2´´ in length along the barrel axis, traversing 90° around the inner barrel, and had a strobe tube diameter of about 3/16´´. (They were, apparently, built by a guy working for NASA’s Jet Propulsion Laboratory (JPL) in Pasadena – fancy that). The inner barrel protected the tubes from the high-pressure CO₂ that was blasted out of the gun (from a little tank about a foot long and an inch in diameter, inside the gun). CO₂ was used to simulate cold plasma coming out of the barrel so as it looked like something was indeed coming out of the gun when the trigger was pulled. This could then be “dubbed” with blue light in post-production. The outer barrel (~3´´ in diameter) was to protect the strobe tubes, because they got “pretty toasty” as Mr. E explains it, and it was of the utmost importance that the talent didn’t get hurt.

By touching them (as with all gas lamps), the oil from the skin reduces their lifespan as it causes gas to leak from the tubes as the natural oils in our skin contain acids that slowly dissolve the glass. In short, the tubes were sandwiched between the inner and outer clear barrel tubes. The outer tubes were made out of the Lexan resin which can withstand up to 115°C before it starts to thermally deform.

External Strobes

The external strobe tubes were on stage, packaged in sheet metal boxes about 12 inches high x 8 inches deep x 3 feet wide. There were four on stage for the effect (with four backups ready if needed). Mr. E was going to use aircraft carrier strobes because his buddy had used those on “War Games“ behind the projection screens at NORAD, but eventually he got them from a company in Hollywood (Lightning Strikes) which makes movie equipment for simulating lightning. Each unit ran on 17.5 kW and contained a single tube about one inch in diameter and about 2.5 feet long. The units were always off camera and aimed on a vector collinear to whatever direction Arnold was aiming the gun in the scene. They were also synced to the cameras´ shutters like the gun´s barrel strobe segments (see below), and were meant to illuminate with flashes, who or whatever Mr. Freeze was shooting.

The tubes were made of quartz and they needed four of these boxed units because if you tried to hit a single one of them, each and every second camera frame, the 2.5 foot long (horizontally situated) quartz tube would start getting too hot. Then the middle of the tube would start sagging, then melting, and it wasn’t pretty what happened after that. So, Mr. E used four, each one only fired when its co-part helical tube segment in the gun would fire. That way, the tubes would only glow orange between strikes, wouldn’t sag or melt, and had enough time to cool before it was its turn to fire again.

Camera Coordination

The helical strobes were to be fired sequentially (back to front) giving the impression of forward movement, or emission from the gun. The inner barrel was blasting the compressed CO₂ at this time, as the trigger pull released the CO₂ and a microcontroller had an isolated input from the trigger and a radio link from the cameras, so it knew when to start triggering the strobe sequence. To ensure these signals were passed along when the trigger was pulled, the antennas on the left side of the gun transmitted a signal to the stage computers to let them know when to start emitting and dimming the synchronized strobe lights.

To be able to see the strobes’ forward movement, each segment had to fire one after the other exposing successive frames of film. So, each strobe had to wait its turn and only fire when the shutters on the three Panavision cameras (gold & platinum), operating at 24 frames per second, on stage were open (which were synced to each other with other circuits). The sequence was something along the lines of 1st strobe (bottom), skip a frame or two, 2nd strobe, skip a frame or two, etc. through the four segments around the barrel going forward in direction and time. There were also a few frames skipped between re-running the sequence of four (if the gun´s trigger was still pulled). This between-time was in frames and controllable via a dip switch (dual in-line package) on the printed circuit board.

Film cameras use shutters which allow capturing an image for a certain amount of time (depending on shutter speed and shutter angle (insert wiki refs)). In order for the strobes to be effectively captured on film, the firing of the strobes (as initiated by the gun) needs to be synced with the camera shutters. This is by straight-forward assignment. By Joram van Hartingsveldt – Own work, CC BY-SA 3.0.

When working on special effects props there are also all sorts of complications that can pop up. Even some human considerations that need to be considered, i.e. the actors wielding said props!

As my anonymous friend Mr. E. puts it: “Now, there were rumors that Arnold’s contract had a stipulation that he couldn’t be attached to, put inside, or made to carry anything operating on over 12V.  We (and probably Arnold’s people) were really committed to the freeze guns being completely without any cables, tubes, or other connections to the outside world. [Having an off-camera umbilical… the usual way to do this sort of thing would have been much easier & cheaper, probably by a factor of 10 w/respect to time & money]. But having seen the cumbersome nature of stunt guys in the freeze suit, we felt that adding an umbilical to the gun would cause freeze’s on camera movements to be even more awkward than the suit alone was causing.  So… no umbilical.”

This meant that there needed to be coordination between the freeze gun Arnold was wielding, the external flash tubes AND the cameras that were recording the entire thing.

Because the cameras were the ‘talkers’ and the gun was one of the ‘listeners’ in this whole thing, the ‘no umbilical‘ situation meant the gun needed to be able to receive camera pulses wirelessly. Since the 70 kV of onstage strobes had to sync with the strobe tubes in the gun, the gun also had to transmit its trigger pulls to stage microcontrollers which, like the gun, were also receiving camera pulses wirelessly (so they weren’t tethered physically to the cameras for the sake of mobility). The gun needed to be able to both transmit and receive pulses and pulse streams. Mr. E didn’t feel comfortable transmitting and receiving in the same part of the electromagnetic spectrum, so incoming receptions were ultra-high frequency (UHF – between 0.3 and 3.0 GHz) and the outgoing were very-high frequency (VHF – between 30 and 300 MHz). Compounding the potential flakiness of this is the fact that film stages are some of the most electrically noisy environments one can work in. Everyone has walkie-talkies, there are multi-kW lighting dimmers everywhere, and there is power from the wall every bit as bad as Vegas. This meant that the probability of missing some of these camera pulses being sent wirelessly was likely at some point. So, Mr. E’s coding tasks including writing a ‘firmware flywheel’ that would precisely time the camera shutter pulses received inside the gun and continue it (autonomously) if any pulses were missed, or garbled in reception, and then resume syncing when transmitted camera shutter pulses became available again.

Based on the ‘nothing-over-12 V-for-Arnold’ rumors, the freeze guns were powered by 9 or 12 V rechargeable Mikita portable hand drill batteries, one per gun. From there, internal circuitry converted some of it into AC, ran that through step-up transformers, and bingo… 8 kV for the strobes. Mr. E was in charge of overseeing the project (8 ‘hero‘ guns (fully operational), and 9 stunt guns (outer blue LEDs only) and 8 ‚thaw‘ pistols) as well as designing and building the microcontroller circuits and firmware for the guns, and stage and camera sync processors.

Over the course of our communications for the past few months, Mr. E has also indulged me with a few nice stories involving some genuine problem solving that I would like to share.

Braiding wires

Mr. E.: “When we were getting to about a week away from camera tests in pre-production, Mr. M came to me and said he’d been trying for weeks, but could not find any way of getting the strobes to fire sequentially without adjacent strobes misfiring due to fortuitous distortion (cross-talk) between the 8kV triggers. He seemed really distraught. So I asked a bunch of questions… how long are the trigger wires…. are they insulated properly….. shielded?…. stuff like that. He’d thought of everything. So I asked him if any of his kids were girls. Yep. So I said, “humor me…take some time in the shop this afternoon, take one of the guns apart, make some new longer strobe trigger wires, and braid that foot of strobe trigger wires, like you’d braid your daughter’s hair”.  Two hours later we were up and running with no more misfires! He also knew the trick… usually used when transmitting high speed data with cmos differential amps, but just hadn’t thought of applying it here; too far in the forest to see the big picture at the time. So… we were stylin.”

Fog and ceramic resonators

Mr. E: “Early camera testing was up at Universal, and everything went well. The only technical error in the design surfaced one morning at the first use of the gun down in El Segundo, I think, right on the docks at the harbor one foggy morning. It was in one of the warehouses we’d used for Rocketeer. Anyhow, when designing the gun’s internal processor card, I found these cool new oscillators called a ceramic resonator. They were tiny, had less leads, and seemed like a great product. That foggy morning in the harbor was their undoing. Got there way too early in the morning, and nothing worked. So… first… always check power & clock. Oscilloscope says no clock. So I call the company that makes the ceramic resonator, and they say that it doesn’t handle humidity very well. Foggy morning on set… fuck!  Long story short, I found some desiccant packs in some empty boxes in the warehouse we were working in, and used a hair dryer on each of the gun’s processor card to dry them out, then wrapped them in desiccant packs before reinstalling them in the guns. Got through the day, and spent most of the night replacing all of the ceramic resonators with proper crystal oscillators.”

Epilogue

There is a bit of irony in all of this. At the end of the day, a whole bunch of goop was animated over much of the movie in post-production. So, considering all the technical prowess, all of the hours, days, weeks and months of camera shutter and flashtube synchronization… most of it was basically dubbed in post. However, the look of the film would have not been the same by any means without the synchronized lighting sequences between the gun and stage strobes, all the stage ‘action’ props and their stage counterparts, so it all added up visually for sure. Admittedly, it still looks great thanks to the immense work put in by Mr. E. and his co-conspirators.

Objectively, Batman and Robin has a lot of cool looking gadgets. And even if critics and audiences alike did not enjoy the film at all, it still involved a gargantuan amount of scientific creativity to accomplish which is beyond commendable and admirable.