Over the last few weeks we have been quietly experimenting with something that has completely captivated us: reverse processed Autochrome plates.

And finally… we have our first successful results.

The images were taken during a recent trip through the Czech Republic, and seeing those tiny glowing colors appear for the very first time on glass has honestly been a magical experience. Even in these early stages, the plates already possess that unmistakable Autochrome atmosphere soft light, luminous color, and a depth that feels almost impossible to reproduce digitally.

What makes them especially exciting is that these are not scans or digitally inverted negatives. These are true direct-view color transparencies created through reverse processing, where the final image is viewed with transmitted light passing through the microscopic color screen itself exactly as the Lumière brothers intended more than a century ago.

And that is where the real challenge begins.

This plate was exposed at ISO 2 • 1/4s • f/11 and developed entirely through our evolving reverse processing workflow. Exposure was metered thru the new ProFilm Metering app we are launching next week!

The Biggest Obstacle: Coating Thin, Even Emulsions in Complete Darkness

When it comes to reverse processing Autochromes, the single biggest difficulty is not actually making the color screen.

It is coating the photographic emulsion.

To make a successful Autochrome positive, the silver gelatin layer must be coated extremely thin and extremely evenly entirely by hand and in complete darkness.

This is absolutely critical because, during reverse processing, the original negative image must develop all the way through the emulsion down to the glass support. If development does not fully penetrate the layer, unexposed silver halides remain trapped beneath the negative image.

And once the plate is reversed, those remaining silver halides become part of the final positive image.

The result?

An image that becomes far too dense, muddy, and dark.

Even worse, that density blocks the transmitted light that is supposed to illuminate the starch grain color screen beneath it. The colors may technically still be there, but they simply cannot come alive because the silver image is physically preventing light from passing through the plate.

This means that reverse processed Autochromes are incredibly unforgiving. A coating that might work perfectly fine for a normal dry plate negative can completely fail in an Autochrome process.

So lately we have been experimenting heavily with emulsions, coating techniques, and development behavior to fine tune the entire system.

One important discovery so far is that lower contrast emulsions appear to work much better for Autochromes. They produce brighter, softer, and more vibrant positives with significantly better light transmission. Highly contrasty emulsions tend to become too dense too quickly, which suffocates the color screen beneath.

We have also found that diluting the emulsion more heavily helps tremendously when trying to achieve thin and even coatings by hand. The thinner layer improves development penetration and gives the final transparency a much more luminous appearance.

Still, hand coating in darkness remains one of the hardest parts of the entire process.

Which is exactly why we are already very excited about the next stage:

dusting the color screen directly onto large glass plates and sending them through the coating machine.

That will hopefully allow us to produce coatings with a level of consistency that is almost impossible to achieve manually.

And yes… another exciting development:

our first tests using infrared goggles are looking extremely promising.

So hopefully soon we may literally be able to see in the dark while coating Autochromes. Which honestly feels wonderfully futuristic for a photographic process invented in 1907.

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Reverse Processing Chemistry Matters Just as Much

Of course, the emulsion itself is only one part of the equation.

The developer also plays a massive role.

For reverse processing to work properly, the developer must be capable of processing the negative image completely through the emulsion layer down to the glass support. If development stalls halfway through the coating, the remaining undeveloped silver halides will again create density problems in the final positive.

And unlike normal black-and-white negatives, Autochromes are incredibly sensitive to even tiny variations in chemistry.

Developer activity, silver solvent behavior, bleaching strength, clearing baths, re-exposure methods everything influences brightness, color purity, and transparency.

Because of this, we already know that if we eventually release Autochrome plates publicly, we will also need to develop a dedicated processing kit specifically designed for them.

That will likely include:

• specialized developers
• bleaching baths
• clearing baths
• carefully balanced reverse processing chemistry
• optimized instructions for consistent results

As always, our goal will be to make the process as simple and approachable as possible while still preserving the magic of historical photography.

Why Autochromes Are So Difficult: The Additive Colour Mixing Problem

One particularly fascinating thing we have been thinking about lately is the actual ratio between the red, green, and blue-violet starch grains inside an Autochrome screen.

At first glance, many people assume the solution is simple:

just use equal amounts of red, green, and blue particles.

But modern RGB display technology actually shows us why things are far more complicated than that.

In many modern OLED displays, the green subpixels are often larger, brighter, or more numerous than the red and blue ones. Why? Because the human eye is significantly more sensitive to green light.

Manufacturers carefully tune these proportions to balance:

• brightness
• efficiency
• perceived color accuracy
• power consumption
• material sensitivity

And that is with modern spectrometers, microscopes, computers, and microscopic fabrication precision.

Now imagine trying to solve a similar optical problem in 1907 using randomly distributed dyed potato starch grains scattered across glass plates by hand.

That is essentially what the Lumière brothers achieved with Autochrome.

The Autochrome Screen and Emulsion Are One Optical System

The real complexity comes from the fact that the Autochrome screen and the photographic emulsion cannot be treated as separate components.

They form a single optical system.

The starch grains do not transmit light equally. Red, green, and blue-violet grains all behave differently. Their transparency, saturation, density, and spectral overlap directly affect the exposure balance of the final image.

At the same time, photographic emulsions are never perfectly balanced either.

Even a panchromatic emulsion which is technically sensitive across the visible spectrum never has a perfectly flat sensitivity curve. Some emulsions respond strongly to blue light but weakly to red. Others have dips in green response. These characteristics shift depending on:

• dye sensitizers
• silver content
• coating thickness
• age of the emulsion
• development chemistry
• processing temperature

This means the starch grain ratios cannot simply be:

“one third red, one third green, one third blue.”

Instead, the ratios must be adapted to the spectral behavior of the specific emulsion being used.

If an emulsion is weak in red sensitivity, more orange-red grains may be required to compensate.

If green sensitivity dominates, green grain density may need to be reduced.

Even the transparency and saturation of the dyed starch grains themselves influence the final color rendering.

In other words:

you cannot optimize the color screen without simultaneously optimizing the emulsion.

And that is precisely why good Autochromes are so incredibly difficult to produce.

You are balancing:

• grain size
• grain density
• random distribution
• color purity
• spectral overlap
• emulsion sensitivity curves
• exposure latitude
• light transmission
• scattering and diffusion
• development chemistry

…all at the same time.

A Century-Old Problem That Still Isn’t Easy Today

When people wonder why Autochromes are so rare, inconsistent, or difficult to reproduce today, the answer is actually surprisingly obvious.

Even modern display engineers with billion-dollar fabrication plants still do not use perfectly equal RGB systems.

And over a century ago, the Lumière brothers were attempting to solve a remarkably similar problem using dyed potato starch grains, carbon black, glass plates, and silver gelatin emulsions.

The more we work on these plates, the more respect we gain for what they accomplished.

We still have a long road ahead, but seeing those first glowing color transparencies appear on glass has already made all the experimentation worth it.

And honestly…

we cannot wait to see where this journey leads next.

If you would like to follow the development of Zebra Autochromes and be the first to hear when we eventually release plates, chemistry kits, and future updates, make sure to join our launch list below.

There is still a long road ahead, but we are incredibly excited to share this journey of reviving historical color photography with all of you ✨