The Autochrome; Color photos? Just add potatoes.
So, it’s the early 20th century. Photography’s been a thing for a while, and simple cameras are hitting the consumer market. So far, though, these cameras aren’t capturing color. Oh sure, discovering a light-sensitive material, incorporating it onto a flexible substrate, and commercializing production and development processes at scale to create a simple, easy, and at least relatively inexpensive way to capture moments in time is pretty dang impressive, but the world isn’t black and white. It wouldn’t be too long, though, until photography got a little more colorful. This is an Autochrome plate, one of the earliest commercially-successful color photography processes.
And it is fascinating in its simplicity, especially given how detailed the images can be. Believe it or not, this is in fact nothing more than an ordinarily black and white photograph. Okay, well that’s obviously not true, whatI mean is the chemistry used to produce the plate and to develop the image is largely the exact same silver-gelatin process we’ve explored in previous videos. The only meaningful difference is a reversal step which creates a positive image on the plate. So… where does the color come from? You probably figured it out by now, it’s potato starch.
Obviously. Let’s back up for a moment. Long-time viewers of the channel may remember the names Thomas Young and Hermann von Helmholtz from my video on analog color television. These two fellas got their names on a theory for color vision which, wouldn’t ya know it, was mostly correct. Back in 1802 Young was like “our eyes, theyprobably have, like, three different color receptors in them” and then like 48 yearslater Helmholtz was like “yeah and I bet one group probably prefers shorter wavelengths, another more medium wavelengths and the third the long ones” and blam we had color vision figured out! Then this Scottish guy, James Clerk Maxwell, thought that maybe we could make use of that knowledge with these camera thingies.
Maxwell reasoned that if a camera could be made selectively sensitive, we could reproduce color by capturing three images which were each composed only of the theorized wavelength ranges. And we could make this selective sensitivity happen with simple color filers. Putting a red filter over the lens would only allow long wavelengths through to the photographic plate. A green filter would only allow medium wavelengths to pass.
And blue, dabba de dabba die, would only allow the shorter wavelengths through. The resulting photographs would be black-and-white, but Maxwell thought that if they were then tinted to match the captured wavelengths, so red, green, and blue, and then recombined through means of projection on a screen, we would be able to reproduce the true colors of the originally captured image. He had this brainstorm in 1855 and didn’t do anything about it for six years. Then in 1861, Maxwell finally put his idea into practice by hiring someone else to do it for him.
That someone else was photographer Thomas Sutton who took three pictures of the same subject, one each through a red, green, and blue filter, and then he made positive copies of these pictures. He tinted them red, green, and blue to match the original exposures, and handed them over to Maxwell where he would wow the Royal Institution with "his" amazing color photograph. And this is it! This is a ribbon made of tartan - think kilt, but bow. And you may notice that the color is barely there. That’s because this barely worked. The photographic chemistry available in 1861 was not panchromatic, so it was mainly sensitive to blue light.
Capturing other wavelengths took much more exposure time, especially red. But this proof-of-concept worked, and when panchromatic emulsions appeared around the turn of the century, incredibly clear color-photographs could be taken with this same method. A few pioneering photographers went through this painstaking process, such as Sergey Prokudin-Gorsky. These photographs of his are all from 1910 or earlier. It’s amazing how good these look, although it should be noted that these are all digitally-created composites. It’s possible that in their time, these were never seen with the fidelity we are seeing now.
This image is presented alongside the original monochrome images. Compare them and you can see how different colors appear as different brightnesses on them. Top to bottom, the exposures were filtered through blue, green, then red. So, by the turn of the 20th century we had a working theory of color vision which had successfully been applied to the photographic process.
This filtered exposure method is often referred to as Kromskop. However, taking three separate images and recombining them after-the-fact is quite clunky, and definitely not suitable for the majority of photographic work. I should note that the practice didn’t entirely go away, though.
Special cameras were made to enable taking all three images at once, and these saw use in certain applications for decades to come. And as a matter of fact Technicolor motion pictures used a very similar technique. The three-strip Technicolor process used pretty much the exact method which produced this image, and it saw use into the 1950’s. I’ve skipped forward in time by bringing up Technicolor.
But as it happens the Autochrome plate has a strong connection to the world of the movies. Its full name is actually Autochrome Lumière as this method was invented by the Lumière brothers, Auguste and Louis. These pioneering French fellas found fame and fortune filming fantastic fights - sorry, sights such as The Arrival of a Train at La Ciotat Station. You know, this little clip. That was shot in 1895. The Lumière brothers started out their business ventures producing still photographic plates, but their foray into moving pictures brought many developments that would bring that industry from its infancy into, like, a real thing.
However, they grew bored of it and thought the cinema had no future. This goes to show that being good at inventing stuff doesn’t necessarily give you a good sense of how the future will go. Anyway, they had been playing around with color photography for some time, experimenting with various techniques such as the Lippman plate which is its own fascinating thing and which I highly suggest you check out. However, that was wildly impractical and so they kept poking around until they landed on this. These plates are an amazingly simple method by which to capture a full-color image. They utilize the same color-filtering technique of Kromskop and Technicolor, but incorporated onto a single plate which could be used in any camera, processed with ordinary chemicals, and which revealed the full-color image entirely on its own.
They patented this method in 1903, and it hit the market in 1907. Before I get into how it works, I need to give a huge thank you to patron of the channel Jon Hilty. Jon loaned me these plates and is among the cool folks out there who are making their own autochrome plates today. And it’s thanks to his knowledge and experimentation that I can share the process with you so completely.
Jon also creates photographs using other ancient techniques, including daguerreotypes! I’ve put links to his Instagram in the description, as well as to his excellent website which includes the Autochrome guide that you can bet I referenced heavily. The Lumière brothers knew that a color image could be captured through three filtered exposures, and presented by recombining them. The genius of the Autochrome plate is the fact that it contains and displays all three filtered exposures all at once. Take a close look at this plate.
See how the solid areas appear sort of… shimmery? Let’s look even closer. That sure looks like a mosaic of reg, green, and blue, doesn’t it? That’s because it is. Well, actually it’s more like blue-violet, green, and red-orange but it works much the same. What you are looking at are tiny, practically microscopic blobs of dyed potato starch. Scatter them randomly on top of a black and white image, and you get a color one.
Well wait a minute, randomly? That can’t work. Actually it can. See, this very plate is what was inside the camera when the image was taken. A random distribution of color dots doesn’t matter so long as it’s the same one that both captures and displays the image. And that is the genius of the autochrome. The mosaic of colored dots is integral to the plate, present from exposure to viewing.
It’s astoundingly simple, yet works remarkably well. Would you like to know how this is done? Well I hope so because I’m about to tell you! These vials contain dyed potato starch. These three powders are all that’s necessary to turn your drab, boring black and white photographic plates into dazzling displays of lifelike color.
But... even just the process of making this stuff is pretty convoluted. First, you want the finest grains of starch you can get. Mixing raw starch with water and allowing it to settle over time allows you to sort the starch grains, as the largest grains will settle first.
You don’t necessarily need to do that, but the finer the grains, the less visible they’ll be in the end. Once sorted to the desired sortiness, the starch is then dyed. Jon uses the original dye formulations for this process to make the autochrome plates as faithful to originals as possible - and that’s why they’re not quite the same red, green, and blue that we’re accustomed to today. If dyed as such this would still work, but the images wouldn’t capture color in quite the same way as they did for the Lumière bros.
The dyeing process is quite involved, and includes not just dyeing but also drying, mortar and pestling, sifting, washing in solvents, and I’m still greatly simplifying here but in the end you’ll have three piles of colored powder, perfect for making color photographs. The now dyed and dried powder is then thoroughly mixed together and deposited onto a glass plate covered in a sticky varnish. That will cause the grains to… stick to it. To assess the quality of the mixture, the grains are crushed using the back of a spoon or something similar. Jon recommends the use of these ball caster things.
Crushing the grains flattens them, making them more transparent and also helping to fill any gaps between them. If in the correct proportions, the mixture will appear a neutral gray on the plate. If there’s too much of a color cast, the mixture should be corrected to compensate. If it looks too green, well remove some green. If it looks too cyan, maybe add some red. And so on.
Once a good mixture is dialed in, it’s time to varnish a new plate, coat the entire thing in the stuff, and get crushing. This is a very tedious process when done by hand, so mechanical aids are a great help. Jon’s been using a fancy CNC router.
Regardless of how it’s done, though, eventually you end up with a piece of glass that has a coating of crushed blobs of color on it. Lampblack may be dusted on at this point to fill in any gaps that exist between the color blobs, though it’s not strictly necessary. What is necessary, though, is that a second varnish coat be applied to seal in the color blobs and make the color blob layer waterproof— a very important step for doing photography things with it.
After that point, this is what you’re left with. This is called the screen plate. And as you can see, from a distance it appears to look grey and uniform. But up close, it’s all blobby and colorful. This forms the critical part of the autochrome plate. I imagine many of you have guessed the next step, and that’s to sensitize this plate using our old friend silver halide crystals.
In the dark, a more-or-less standard panchromatic silver-gelatin emulsion is coated directly on top of the finished screen plate. Special considerations need to be made in the formulation of the emulsion, mainly due to the need for a very thin coating, but otherwise it’s the same black and white chemistry you find in a roll of Fomapan. Once dry, the finished plate can be placed in a light-proof plate carrier for later use in a camera.
Compared to most plates, an Autochrome plate is loaded into the camera backwards. Rather than have the captured light land directly on the emulsion, we need it to travel through the screen first, and that means it will also travel through the thickness of the glass. This requires special focusing considerations in the camera but is otherwise trivial. In the camera during the exposure, the screen-plate causes the same short, medium, and long-wavelength filtering that happens in the three separate exposures of the Kromskop process, but now all at once on the same plate, hyper-localized on tiny portions of the emulsion. The areas behind the green blobs will only be exposed to medium wavelengths.
Those behind red-orange blobs will only see long wavelengths. And behind the blue-violet blobs, only short wavelengths make it through. After exposure in a camera, a latent image is formed on the plate and it’s ready to be developed. You may recall that the silver-gelatin process produces a negative image.
Areas that were hit with light in the camera become dark areas in the processed image because light-blocking silver grains form in the development. That wouldn’t be useful here, however a fun little secret of the silver-gelatin process is that it can rather easily be tweaked to form a positive image rather than a negative. Remember the step of fixing? That turns film from cloudy to clear because fixer dissolves the undeveloped silver halide crystals in the emulsion. Usually this is what we want, but if we don’t fix the film (or plate) we’re presented with an opportunity. In the developed-but-not-fixed state, the emulsion contains both the negative image made of silver but also its inverse made of the undeveloped halides.
That means they’re a positive image just waiting to happen. Luckily, chemicals exist which will dissolve developed silver but which will leave undeveloped silver halides alone. In photography these chemicals are known as bleaching agents, or simply bleach. Develop a plate, and as normal that darkens all the exposed areas by converting those halides to pure silver.
But if your next step is to remove the silver through bleaching, you now have a plate which has had the components of the negative image removed but which still has the undeveloped silver halides everywhere else. Rinse away the bleaching agent, and you can now expose this plate to room lighting which forms a latent image on all the remaining halide crystals. Simply develop the plate a second time, and all remaining crystals become converted to silver. With the negative image already disposed of now you’re left with a positive image! In the case of the autochrome, this has a fascinating and fortuitous result. Areas behind red-orange blobs which got hit with long wavelengths in the camera become transparent since they were converted to silver in the first development bath but that was washed away in the bleaching step. If they weren’t hit with long wavelengths, those areas are darkened in the second development since the silver didn’t form in the first.
The same filtering phenomenon goes for areas behind the green blobs, and the blue-violet ones. If they were hit with light, they’ll be clear. If not, they’ll be dark.
And since the screen plate is still there, and it’s the same one which divvied up the plate’s sensitivities in the exposure, the captured image can be viewed in full-color simply by passing light through the plate. The same blobs that did the filtering in the exposure do the coloring in the presentation, and just like that you have a self-colored plate. Or, you might say, auto-chromed plate. Isn’t this just fascinating? Aside from the reversing step, there’s nothing special about the chemistry here at all. This is the same black-and-white photographic process that produces film like this.
As a matter of fact, on some of these plates if you look at the emulsion-side you can see the silver glistening in the right light, just as you can with a piece of film. Yet a simple mosaic of colored potato starch manages to turn that process from monochrome to all the chromes. Yeah, okay, making the screen plate is a really fiddly process but conceptually it’s profoundly simple.
It’s almost amazing that this works at all, let alone this incredibly well! I mean, really, these are striking in person and I hope my camerawork is doing them justice. I should note that the autochrome wasn’t the only color photography method which worked this way. As a matter of fact, an earlier screen-plate process invented by Irish physicist John Joly used a screen consisting of very fine alternating red, green, and blue stripes. This screen would be placed in front of a photographic plate during the exposure, then a contact print would be made from this negative to create a positive and a second color-stripe screen similar to the first would be placed over it for revealing the color.
This was produced commercially in 1895, but likely due to some combination of not-quite panchromatic emulsions of the time, fiddly alignment requirements, and the very noticeable color screen, it produced unsatisfactory results and didn’t last long. What’s fascinating to me is how the autochrome almost seems to blur the lines between the analog world and the digital one. Of course there’s nothing digital at all about them, but take a close look at these - and by close I mean really, really close - and you see that this works exactly like the display you’re viewing this video on. This red, or I suppose coral watering can? Well, up close it’s clear that it’s mainly the red blobs that are visible and the green and blue blobs are kept mostly dark by the silver in the emulsion behind them. It’s weirdly like how an LCD works, as a matter of fact it is crystals selectively blocking light as it travels through color filters. Just like the phosphor dots on a CRT these are not pixels, but man do they kinda feel like them.
As a matter of fact, this is quite similar to how modern digital cameras work. The image sensor in a camera isn’t able to differentiate between wavelengths of light on its own. So, in front of the grid of many millions of discrete light sensors that will eventually make the pixels you’re seeing now is the Bayer filter. This is simply a color filter in a repeating pattern. It’s aligned carefully with the actual sensor elements so that each one only sees red, green, green, or blue wavelengths. The camera’s software knows which sensors are seeing what colors, and in a process known as debayering, the camera decides what color each pixel should be in the final image.
So how’s that for a technology connection? There sure is something wild about seeing that concept in the most analog of ways, isn’t there? Especially since it works so well. Jon’s home-made autochromes have a coarser screen plate than those which were mass produced about a century ago, but in a way this only adds to their beauty and charm. Seeing modern subjects represented in this way is quite the experience, it’s almost dreamlike. Plus, I’ll be honest it’s been really handy for gathering B-roll because even these grains are quite small.
To get this footage, I have an extension tube on my camera lens and the lens is literally touching the glass. This really is borderline microscopic. Want to see an image captured on a mass-produced plate? Well, take a look. These antique autochromes of unknown age are frankly striking in their sharpness and color fidelity. With the naked eye, the only thing that’ll tip you off to their autochromeyness is that slight dithering you see in solid areas like the sky.
Which is another way these look weirdly digital, by the way. It looks kinda like sensor noise to me. Anyway, when I saw these I was astounded. I’ve seen samples of autochromes online, but until you hold one in your hand you really have no idea how lifelike these can appear, especially with large plate sizes like these. Frankly, if I didn’t know any better, I’d think this was taken by a camera made in the last decade. Yeah, there are some areas where the mosaic is a little messed up, maybe it was damaged in processing or something, but particularly this image? It’s just fascinating.
It’s like looking at a giant piece of slide film. Except for one problem. So far you haven’t seen me hold one of these in my hands. That’s because this is what they look like.
Right… so the screen plate, since it’s a mosaic of intensely colored blobs, is quite dark. And only the very lightest parts of the image will appear that "bright." To show any detail or color, the image gets darker than the baseline of the screen plate so, yeah, these things are dark. This isn’t something you can simply hang on the wall and display, or even keep on your desk.
You need bright light shining through it to see it properly. Back in their day a special holder called a diascope would allow you to view these with some level of comfort. These were really just cases with a mirror so that you could position the plate towards something bright - like, perhaps, sunlight coming in through a window - and look down at it, relieving you from having to hold it in front of your face like this. You might have guessed, then, that this also made taking them difficult.
And you’d be right. Since the actual photographic emulsion was sitting behind something that filtered out the vast majority of light that went through it, you needed a lot of light to expose an autochrome plate. Exposure times were thus quite long, making a tripod a necessity and limiting the use of these plates largely to landscapes and still lifes. Capture a moving subject you will not. Oh, and also, at least in the early days you needed a color filter over your camera lens to compensate for the effects of UV exposure and to increase color fidelity, so you were also losing light from the start. Still, despite all these drawbacks, the ability to load a single plate into a camera, use ordinary photographic chemistry, and end up with a full-color image was unparalleled for some time.
And they were very commonly used! Remember, these were mass produced and sold ready-to-use, and many turn-of-the-century photographers had their go at color. Vast archives of autochromes exist in various collections, and thanks to the fact that the image is made from stable silver and the colors are produced by dyed potatoes sealed in gloop, many are holding up remarkably well. Autochrome plates continued to be produced into the 1930s, and as a matter of fact, the technique lived on beyond the plate and into the age of film.
However, thanks to its shortcomings, more flexible, higher-tech methods would soon displace it. In a later video, we’ll take a look at these technologies, but for now— my hat goes off to Jon Hilty. People like him who keep these old techniques alive not only through documentation but through actually using them are pretty cool. Sure, not many people are taking pictures like this these days.
But I’m very glad at least a few are, and I’m very grateful to have been able to share this with you. Thanks for watching. ♫ convolutedly smooth jazz ♫ …at scale to create a simple, easy, and rell AAAGGH to create a simple, easy, and at least relatively inexpensive way to capture moments in time is pretty dang expensive! Ugh. Impressive! Oh, sure, discovering a lime-sensitive mate… haghh! Ya know, this little clip? Agh, buttons. But even just the process of… [noises] Special considerations need to be made in the formulation of this emulsion, mainly due to de the de de de de theehh de du duh beh beh ...is that slight dithering you see in solidareas like the sky. Solidareas? Solidarity with solid areas? Anyway, when I saw these [rumble from above] Great.
What else can potato starch do for us? Who knows what many wonders we might have yet uncovered. Why, perhaps potatoes are the secret to time travel! Probably not, but then again one of the best ways to spice up your potatoes? It's only a matter of thyme.
2022-04-27 17:28
