To understand some of the later issues in transferring movie film, it is first required to understand something about film itself, how it's manufactured and how it degrades. This is not an attempt to delve deep into the chemistry and physics of of it, but a general discussion written simply as possible for those without a BS degrees in chemistry, to describe in general terms how it works, it's characteristics, weaknesses and how it degrades..
There are many types of films, but for home movies that could be projected onto a screen, we will limit the discussion to color reversal film: specifically; Kodak Ektachrome which became the most popular in the US in the hay-days of Super8. Kodachrome required a slightly different process than did Ektachrome, but in general terms, it worked pretty much the same conceptually..
Just like video or audio tape, film requires a base or substrate to which layers of light sensitive materials are applied to give it both strength as well as flexibility so that it can punched with sprocket holes as well as withstand the rigors of being run thru a projector without being totally destroyed in the process. That is pretty much the only purpose the film base serves... The acetate base of film is akin to our bones... It provides the high strength necessary to allow handling while remaining flexible.
The most common material used is cellulose acetate... It is made usually from wood pulp that contains cellulose fibers (wood fibers) and mixed with acetate to form something akin to a gooey (the scientific technical term) syrup... Acetate by the way is derived from acetic acid. As a side note, if acetic acid sounds like you heard of it somewhere before. it's because you have ! Acetic Acid is one of our body's building blocks for making protein.. The form of acetate made for making film has some unique properties and is similar to a polymer (plastic) and when mixed with cellulose, makes for a strong, durable, highly flexible material that does not fatigue. Another of it's physical attributes is it's resistance to tearing... That means one can punch square sprocket holes in it (we'll cover that later) without the film tearing at the corner stress points of the holes as it is flexed.. Another of it's main attributes, is that it's CHEAP ! That's a hard combination to beat !
Cellulose acetate is actually an amazing material when you come to think of it.. When it comes to making and selecting materials Mother Nature uses for her building materials, one has to conclude that Mother Nature is no dope !
Films prior to 1948 used cellulose nitrate.. Sometimes called nitrocellose or simply shortened to nitrate films... The big downside to this material was that it was highly flammable. When cellulose acetate was used to replace it, it was dubbed "Safety Film". For those old enough to recall the packaging on Kodak ® films, "Safety Film" was conspicuously printed on the box. Now you know where that term came from... It was more than just a catchy marketing phrase; it literally was a safety film... Much better chance you wouldn't burn your house or the movie theatre down ! Nitrate based film also tended to degrade more rapidly then it's later to come counterpart of acetate.
Anyways, the cellulose acetate base is simple, but so necessary that it warranted some mention... It is also called cellulose triacetate..
There are other film bases such as diacetate which was popular in the 1920's to the 1930's and polyester started being used around 1980.
Black and White Negative Film
Though home movie films are all color reversal (color positive) or Black & White positive, it helps to first understand how simple black and white negative film works.
Film Emulsion - What gives film it's light sensitivity
It starts with pure silver which as some very interesting properties because of its' many free electrons. Because of this, silver is also an excellent electrical conductor... but I digress. The film manufacturer purchases highly pure silver bullion which is then put into a nitrate bath which then dissolves the silver. What's left is a solution rich in silver nitrate. When dried, silver nitrate crystals are what's left. Silver nitrate which might come as a surprise, is not light sensitive at all. But silver halide crystals are. So the final step of turning silver nitrate into silver halide crystals must be done in complete darkness.. (No peeking in to see how the "brew" is coming along !)
Once you have the silver halide crystals, the next step is to layer it upon the film base... To do that, you can't just sprinkle them on as they would just fall off. So you need an optically transparent carrier that acts as a binder similar to how the magnetic particles making up video tape is bound to it's base.. Only this "binder" must be optically transparent..
What fits the bill is simple gelatin... Yes this is the same gelatin derived from collagen found in the bodies of both us and all animals. It's used as a jelling agent. ( They don't call it Jell-O ®, for nothing !) You can pick up a small bottle of pure gelatin at your local pharmacy to make your own salves.. Anyways, the silver halide crystals are mixed with the gelatin and applied to the cellulose acetate film base to form the thin photo sensitive layer.
What gives silver halide crystals it's light sensitive properties you are probably asking ? Note: a detailed explanation of the chemical processes and physics of how this happens is beyond the scope of this page, but there is a wealth of material written on the subject for those wishing to know. So what follows is a very brief description.
In short: When a photon of light energy of the appropriate wavelength strikes the silver halide crystal, the crystal structure changes and silver atoms are created converting the silver halide to metallic silver wherever it had been exposed to light.. This forms the latent image... The chemical developer turns the metallic silver in to Black Metallic Silver which is now opaque... Thus wherever light struck the film, what is left is black metallic silver in an amount proportional to the light exposure... The size of the silver halide crystals determines obviously the grain size of the film but the size of the grains also determines how sensitive the film is to light. (Generally known as the film's speed)
This is a negative film... There is a lot written on the web delving into the chemistry and physics of it, but this should provide a basic understanding of what is going on....
That's fine, but you can't project a negative image - you need a positive image. Great for making prints though..
Black and White Positive Film
The process compared to negative films remains essentially the same with some notable if not interesting differences such as how it' s done.. The negative is converted to a positive by the use of a bleaching agent that turns the metallic silver back in to a silver halide again where it is removed in the final fixing and wash steps... Voila: now you have a positive.. This is a somewhat highly simplified explanation, but should be enough to grasp the concept...
Color film is a bit move involved, but still basically the same...
Color Positive Films actually all use the subtractive color method where instead of Red Green and Blue, it uses Yellow, Magenta & Cyan. In the Cyan, Magenta, Yellow system, the top yellow layer is actually recording the Blue information, the middle Magenta layer records the Green information and the bottom Cyan layer is recording the Red information. But most people relate better to RGB color. So I will describe it that way...
Color film uses essentially the same processes as before. The difference is that instead of one light sensitive layer, there are now 3 color sensitive layers. The Blue layer, Red Layer and finally Green layer...
The very top layer where the light enters is a clear protective gel. It serves only to protect the layers below
The next layer is the Blue sensitive gelatin layer. It's made from the same silver halide crystals but has been doped with a blue dye and the silver halide crystal structure slightly modified to be sensitive to the shorter blue wavelengths.
The next layer is a Yellow filter.. Again, a gelatin layer but containing a yellow dye.. The purpose of the yellow dye is to filter out the blue light to make certain no blue light wavelengths reach the Red or Green layers. Reason: both the R & G layers have a slight undesirable sensitivity to blue wavelengths which would throw off the color balance..
Next comes the Green gelatin layer who's purpose should be obvious by now. Naturally it contains a Green dye...
Next; a clear gel layer. It serves only to separate the Green from the Red layers.
Then the Red gelatin layer which contains the red dye
Then comes the antihalation layer. This serves two purposes... It binds to the film cellulose acetate base but also serves to prevent any light making it past all the above layers from being reflected back..
Naturally then the film base itself.
Finally at the bottom of the "heap" is the antistatic backing... As it's name implies, that' s what it's for..
Color reversal film uses the same basic bleaching steps as does Black and White positive film.
Point of interest: The process of making a positive film by adding a bleaching step, was termed chroming... Hence the product names of Kodachrome and Ektachrome; both which are color positive films. Now you know where the "chrome" came from !
Kodachrome films are more color fast... In Kodachrome film, the dye is not impregnated into the respective layer of the film, but rather introduced in the developer stages where the dyes are then effectively transferred to the film. Ektachrome is less color stable over time, but the process of developing it is much simpler.
Now that we have the film made, the next problem is to determine how the camera knows how to position the film for exposure..
The solution to that problem is sprocket holes... Sprocket holes in film is the logical equivalent to the control track pulses for video tape... It lets the playback equipment know where each frame is physically located on the film. The manufacturer simply punches square sprocket holes in the film. In the case of 8mm, Super8 and Sound 16mm, there will be sprocket holes on one side of the film. For earlier 16mm silent films, sprocket holes were punched on both sides. When sound came, they had to make room for the optical sound track, so all sound film by default has sprocket holes on one side only...
The spacing and size of the sprocket holes is cast in concrete by agreed on standards to ensure the film will fit and project properly no matter the film, camera or projector manufacturer... There is one sprocket hole for every individual frame of film..
This will be further explained when we get to discussing how home movie cameras work.
Like everything else, nothing lasts forever, and that especially includes film.
Vinegar Syndrome - Warped - Buckled - Brittle Film
This is undoubtedly the most deadly. It is simply the breakdown of the acetate, turning it back in to acetic acid again. Vinegar Syndrome as it is called, gets it's name by the odor given off by the acetic acid as the acetate base breaks down. Diacetate base films go through a similar breakdown, but smells more like mothballs. For whatever reason, the term "mothball syndrome" never caught on, most likely since most movie film was cellulose acetate...
What causes it you might ask ?: The acetate is acidic. When moisture in the form of humidity in the air interacts with the acidic acetate in a process known as hydrolysis, that triggers the breakdown. Water is simply natures most plentiful solvent.
Films that emit a vinegar odor are out-gassing. That is; in the process of breaking down. The only option is to get the film transferred before it is too late... There is no real cure for it.
What happens when Vinegar Syndrome begins and is left to run it's course you might be asking ?
Film becomes brittle. Bend it slightly, and it will break. Since most movie protectors have anything but a straight film path and the film has to start and stop at each frame, that puts a lot of stresses on the film. In the latter stages of degradation, attempting to put such a film into a projector can turn it in to "confetti" for lack of a better description
Warping: Degradation begins at the outside edges that are directly exposed to the humidity in the atmosphere and thus break down first, while the inner part of the film is more protected by the adjacent wraps of film.. When that happens, the film in addition to becoming brittle, will also begin to curl and warp.
If left unchecked, the film can turn so brittle that any attempt to project it can turn it in to confetti... In the final stages, the film will weld together, making it impossible to even separate it.. In the final stages, there is no cure.
There are several "outs" as it were....
First, the degradation can be drastically slowed or even halted (not reversed however) by freezing the film. Don't just toss all your precious home movies in your home freezer and pray for the best however. To be successful, you first have to prevent condensation from forming . There is a lot written on the topic of freezing film already, so no sense repeating in.
A lot of blogs and suppositions about using special chemical baths to rejuvenate the acetate to restore it's flexibility. Claims that leaving a film to soak in FilmRenew ® will somehow perform some chemical magic akin to how a meat tenderizer does with something less than a prime cut of steak. In reality, if it does anything, it is not effective or consistent enough to do much - not for films who's acetate base has started to break down anyways.. Many claim to have special secret chemical treatments that can perform nothing short of miracles and resurrect badly brittle-warped films from the dead... Beware of anyone making such claims... Trust me: if there were any truth, manufacturer's such as Kodak and Fuji would be beating the drum loudly about such miraculous "cures" and would be in their interest in making the information widely available. Professional film archivists would be beating a path to anyone's door who could actually pull off such chemical "alchemy". Alas, they are not...
This is actually a solution if the problem is caught in time. Effectively we make a contact print of the original film onto new film stock. The film must still be flexible enough so that it can be pressed flat.. The downside: It's expensive !
Instead of making a reprint, the film is held flat and perfectly registered onto a slightly modified flatbed scanner and an image is taken of every frame... This works well - in fact amazingly well. The problem is that it is extremely time consuming and thus quite expensive. When there is no other out, this is the best technical solution (Money not being the issue anyways.).
If you have vinegar syndrome films, the first step is to keep them segregated and away from your "healthy" films.. The out gassing can attack other films close by. Also do not keep vinegar syndrome films in cases or cans. It is best to let them breathe freely. The cases retain the acetic out gassing which only serves to speed up rate of degradation.. It's almost like a cancer in that once started, it tends to spread rapidly.
In the end, the best solution by far is to have the films transferred before the acetate base begins to break down in the first place.
Polyester film bases that started to appear in the 1980's do not suffer from the vinegar syndrome... Reason: No Acetate ! Some Fuji films used a polyester base. (Polyester is a plastic)
How do you tell if your film is polyester or acetate ??? Hold it up to a bright light and look at it edgewise. If it's acetate, it will appear to be somewhat translucent. If it's polyester based, then it will appear black or opaque... Also, polyester will not tear... Acetate will.... That's how you tell !
All home Movie Films use color dyes as opposed to color pigments which are far more color stable. Eventually over time, all dyes will start to break down and thus fade. (Not unlike us in many respects !)
Early color films up until the 1980's were notorious for quickly fading - especially the cyan dye which would result in an obnoxious red or orange hue. From then on, stabilizers were added that slowed the process, but given enough time, all films will color fade...
The left image is the color with the light source color temperature at a standard 5600 degree Kelvin. The cyan dye is clearly fading, resulting in a red/orange hue. Color correction can restore the color balance to normal as evidenced by the same color corrected image on the right. (Yes folks - that's me in 1969 taken with my Mom at the end of Basic Training at Ft Polk, LA.)
Unless the cyan dye has completely faded, the film can often be color corrected. This can be accomplished at the projector itself by using an adjustable color temperature light source, or it can be accomplished via video color correctors in the form of hardware or software..
Color balance is exactly as it's name implies. It means restoring the color balance.. For example a grey image is made up of equal parts of Red Green and Blue.. If the image has an orange appearing cast to it, it means the image is deficient in blue, leaving only equal amounts of Red and Green.
There are 2 solutions to obtain equal amounts of Red Green and Blue..
First is to equally reduce the amount of Red so it comes into balance with Blue and red... This has the advantage of not increasing chroma noise if done in post, but has the downside of resulting in lower overall chroma levels. Those levels can then be boosted later, but at the expense of chroma noise.. If no Red information exists at all, then both Green and Blue channels would also have to be reduced to zero to maintain color balance, resulting in a monochrome image...
The other option is to maintain the Red and Green Levels and to simply boost the Blue channel... That works, but only if there is enough Blue to boost in the first place... No matter what the technique, there must be something left of the faded color/dye to allow a color balance without ending up with a monochrome image..
To keep costs within reason, color correction is usually done globally. By that I mean that large sections of the film have one color correction used... Often times, color fading can be different even between adjacent frames... The cost of color correcting and matching each series of frames to prevent color flicker is horrendous because of the time involved.. In the case of "Gone With The Wind", the 1998 restoration process was a daunting one. The most degraded parts of the film required special techniques. EDS Digital Studios (a Los Angeles based restoration company) spent more than 12 months digitally restoring the most seriously damaged parts of the film . EDS assigned 30 visual-effects artists to the project, who worked frame-by-frame to restore 18,000 frames - which translates into but 12 minutes and 30 seconds of film. Cost: about $10.2 Million... (Perfection is expensive !)
Even although the film has escaped the ravages of acetate breakdown (Vinegar Syndrome), the colors have not faded or the film scratched, it might not have survived a projector that was rough on the film and caused damage to the sprocket holes.. The exact size and shape of the sprocket holes determines how exactly registered the film will be positioned in the film gate... Worn sprocket holes results in "jumping images" (usually vertically)... All films wear with repeated use, but some projectors can be especially brutal on film.. Most damage occurs at the sprocket wheels just before and after the film gate. If the loop is lost often due to a worn claw. The claw tries to pull the film into position when there is no slack in the film... In that case, something has to give, and what often gives is the sprocket holes. Many times such damage is due to mis-threading and failure to form a large enough loop...
The are software solutions known as image stabilizers or de-shakers that can minimize the effect, by shifting similar points in between frames so that they line up.... But it means slightly zooming in to prevent black bands from appearing as the image is shifted trying to align it... That by far is the most cost effective solution. But there are limits and trade offs to be considered.
The other option is to have the film contact printed onto new movie film stock. Unless the damage is too great, that is usually effective. Unfortunately, it's also quite expensive and beyond what most people want to pay...
Mold can grow on film as it can on video tape, or anywhere else there is moisture, relative darkness and an adequate food source... Above all, keep films in a low humidity environment. All strains of mold (there are over a thousand of them) require moisture to grow. It is one more reason why you never want to touch the film with your fingers. The fatty oils left behind provide an excellent food source for future mold to grow... Read more on film storage below
Water damaged movie film can be a real problem... often times a fatal one...
The greatest risk is that the emulsion layers can delaminate from the film base... When that occurs, it's "Game Over"
Flood waters pose the greatest danger because of the solvents such as greases, oils, paint thinners, gasoline etc that flood waters often contain.. That usually proves instantly fatal to films...
If the water is clean there is still a chance the film can be properly dried and transferred... Time is of the essence in such cases. In the case of flood damaged films, contact us immediatlely for instructions !
All film is susceptible to being easily scratched and scored.. The most common reason by far is attempting to play a dirty film without first being properly cleaned.. The debris acts as an abrasive. Small bits of hard debris get jammed in the film gate and scratch the film just like taking a rock and dragging it over the paint on your car. The damage is permanent... Cleaning and lubing the film films fill in the faint scratches but the deep scratches are there to stay..
The are two ways of minimizing the apparent damage... First clean the film and use a rejuvenator that can chemically fill in the small holes and scratches. It can hide many of the smaller defects. Kind of like how a windshield repair kit fills in the small voids... The other option is to run the video thru a high end noise reducer which is what we use here... There are other software solutions, but they tend to be tediously slow to render.
There is "wet gate" transfer system that can make a huge difference on such damaged films. It is rather expensive
Best solution is to only run a film through a clean projector and keep the film clean as well.
There are so many articles on the web written on this topic alone, that it would be a waste of time to just repeat them here.
Here is a good jumping off point. http://www.paulivester.com/films/preserve.htm
By now it should be clear that movie film is far from being an ideal archival medium and eventually all films degrade - it's just a matter of time.
The only out is to have the film transferred to a digital format where it can be losslessly replicated ad infinitum.
Last Modified: Apr 4, 2011
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