I was pleasantly surprised by my trip to the bank. You see, the average salary in Britain would probably be somewhere between £80-£100 a year, but that had to support a family and would mostly get spent.
While I was a private, I was paid a shilling a day, while a lance corporal 1 shilling and 3 pence, and while a sergeant 2 shillings and 4 pence. While hospitalised, I continued to earn a shilling a day as a private. After losing my leg, it counted as a major disability, and I got a hundred percent pension of 27 shillings and six pence per week.
The war gratuity I received at the end of the war was paid at 5 shillings a month for a private, 7.5 shillings for an LC, and 15 shillings for a sergeant.
In total it was 2571.7 shillings in wages, 4766 shillings in pension, and 522.6 shillings, or about £402. On top of that, I would continue to receive an annual pension of £71 and 10 shillings for the rest of my life. It was enough to live modestly or to supplement whatever could be earned as a civilian.
Four hundred quid was not enough, however, to get an engineering degree. Well, it probably was, but I would have nothing left at the end and would need to find a job for a few years before saving up enough to develop a product; I would just have to jury-rig a system and get on with it.
If I'm going that route, then it's more than enough for now; in fact, one could probably buy a decent home in some areas with that much. The fact my father had some of the equipment I would need combined with the fact I had next to no living expenses for now meant my goal was quite achievable.
I just need to get started.
Without modern analytical tools, trial and error would dominate development, so it was best to get started immediately, and after convincing my father that I had an idea, he agreed.
Kodachrome was based on the subtractive colour model, using cyan, magenta, and yellow dye layers. The steps I would need to perfect to do this were as follows: Create three separate emulsion layers sensitive to blue, green, and red light, respectively. Use sensitising dyes to make each layer sensitive to a specific wavelength. Find a way to produce dye molecules during development that correspond to each primary colour layer. And finally, ensure the dyes are stable and do not bleed into other layers.
Another issue was which film to use; I would prefer to use cellulose triacetate, but that required lab conditions, and I didn't have the resources for it.
Cellulose nitrate was basically used everywhere at this point but was highly flammable and burnt intensely, leading to several massive fires, and is prone to chemical degradation over time, leading to "nitrate rot," which can cause the film to become brittle, sticky, and unusable.
Cellulose acetate was the best to use, but it would be another ten years before it became even half as clear as nitrate film.
Guess we have to invent that too.
My dad's deep knowledge of film was incredibly helpful, though he seemed more interested in a non-flammable film than colours.
I mean, he has a point, but why not do both?
Anyway, a few days later, several bags of cotton linters, which were the short fibres left on the seed after a gin had removed the longer staple cotton fibres, along with drums of acetic anhydride, sulphuric acid, sodium hydroxide, acetone, and triacetin.
The triacetin was a polymer coating and was a pain since most polymer coatings around were camphor, which was basically acid to acetate film, so I had to shill out like £50 for the stuff since very few places made it, and I had to get it shipped from the states, which delayed us by two months.
We started by washing the cotton linters in water and then bathing them in sodium hydroxide to remove further impurities.
Then rinsed once again in water and then dried, we then add it to a vat along with acetic acid to partially swell it and continue to add more acetic acid to the mixture until it is fully absorbed. Small amounts of sulphuric acid are added to catalyse the reaction, converting cellulose into cellulose triacetate.
It took a few weeks of trial and error to adjust the reaction time or add water during the reaction to hydrolyse excess acetyl groups, yielding cellulose diacetate, which was less brittle and more suitable for film.
We then had to neutralise residual acid by washing with a dilute sodium bicarbonate solution, which removed unreacted acetic anhydride or acid, which could lead to acetic acid production later. Big no-no.
We then added hydroquinone to minimise oxidative degradation and magnesium oxide to neutralise any further acetic acid that might form over time and prolong shelf life and film stability.
We then had to dissolve the cellulose mixture into acetone to start the casting process. Next the triacetin polymer is added, which will give the film more flexibility and durability. It had to sit in an airtight container for a few hours to allow air bubbles to rise to the surface. If we just poured it now, we risked the acetone evaporating before sir bubbles escaped. Once we were sure it was properly mixed and had no microscopic air pockets, we continued by spreading the solution thinly on a flat surface and smoothing it out with a spreader and allowing the solvent to evaporate, leaving a flexible film behind after a few hours.
Heat treatment is the next critical process used to relieve internal stresses, improve dimensional stability, and enhance the overall mechanical properties of the film. This process helps the cellulose acetate film achieve the desired balance of flexibility, durability, and optical clarity.
I cried at the amount of losses we had to burning, warping, or melting.
It starts by baking the film in an oven at around 40-50 C for a time to make sure all moisture and solvent had been evaporated, and then we had to slowly raise the heat over the course of a few hours to somewhere between 90-130 C.
After heat treatment, you need to rest at room temperature for a few hours to reset, and then the film may be trimmed, slit, or rolled into the final desired shape.
We probably went through close to a thousand batches before nailing it. Too brittle, too soft, too misty, it has air bubbles, it's too thick, it's too thin.
I cried that night; we had made five batches in a row, and they had all come out perfect.
Step One Complete.
"Henry, are you sure you want to chase colour film? People have been trying for the last fifty years. You've just invented an inflammable film that hopefully has a much better shelf life. You could sell the patent for a few thousand pounds and never have to worry again." My father said over dinner.
I smiled hearing the genuine mix of curiosity and concern in his voice. I just smiled and replied. "Father, I know I could, but it would most likely take several years to adopt, and some people would refuse to adopt it solely because what they're used to is good enough. Please trust me when I say we can do this."
"Alright," he said.
The next day we got to it, and I tried my best not to cuss.
"What's wrong?" My dad asked if I was now used to the fact that I rambled to myself a lot after coming back from the war.
I sighed, pinching my nose as I said, "None of the dyes that we can get are stable enough not to bleed into each other. I have some ideas; it's just going to take time..."
"Well, we got time." he responds
I smiled at his optimism and continued, "...and money. Which we are running out of."
My father popped out for a bit and then came back with a letter. "There, I just mortgaged the shop; let's get on with this."
Even though it wasn't proper for the time, I hugged my dad. "Thanks."
"Please. You're my son," he replied.
Colour mixing with subtractive colours makes my head hurt but works like this.
Cyan + Magenta = Blue (Red and green wavelengths are absorbed, leaving blue.)
Cyan + Yellow = Green (Red wavelengths are absorbed, leaving green and blue; together, they appear green.)
Magenta + Yellow = Red (Green wavelengths are absorbed, leaving red and blue; together, they appear red.)
Cyan + Magenta + Yellow = Black (All wavelengths are absorbed, resulting in no reflected light.)
I would need to 'invent' synthetic dye couplers, so I just decided to steal Kodak's work again.
Their yellow coupler was called dichlorophen-chlorophenyl-methyl-ethyl-triazine.
Their Magenta Coupler was called Dichloro-phenyl-methane-sulfonyl-phenyl-phenyl-oxadiazole.
Their cyan coupler was called chlorophenyl-chlorophenyl-ethyl-triazine.
Okay, so for the yellow dye, the challenge started with getting this triazine structure just right. You know, a triazine ring is like a puzzle, three nitrogen atoms in a cycle, and we needed to build it so it would react with an aromatic compound to make the colour happen. Now, we didn't get it right the first time... or the second. It took months of trying different combinations of chemicals to get that perfect balance.
First, we started with dichlorophenol, which has two chlorine atoms on the ring. Then, we tried attaching this triazine ring that was also chlorinated and had an ethyl group sticking out. The trick was getting the right reaction between the triazine and phenol so we could get those two to bond, but in the right way. Sometimes we'd get something close, but not quite right, and we had to adjust temperature, solvents, and timing until we nailed it. The trick was making sure that everything lined up to form that strong bond between the two rings.
After many, many failed attempts and tweaking the recipe, we finally hit on a mix that gave us the right yellow! So yeah, it took forever, but it was totally worth it in the end.
Now, for the magenta coupler, that one had its own challenges. This time, we were working with an oxadiazole ring. It sounds fancy, right? But the real challenge was getting two aromatic rings to bond with the oxadiazole ring in just the right way.
We started with dichlorophenyl and methane-sulfonyl-phenyl. The goal was to get these two groups to connect through a ring structure: the oxadiazole. But let me tell you, those aromatic groups didn't want to cooperate! We had to carefully choose conditions to make the cyclisation work so that the two phenyl groups could lock in with the oxadiazole.
We also had to figure out how to introduce the sulfonyl group. Too much, and it wouldn't form the right structure; too little, and we couldn't get the colour we needed. There were a lot of trial runs where things either didn't connect, or they connected in the wrong positions.
But with months of adjustments, different temperatures, solvents, and times, we finally got the right product. The trick was finding that sweet spot, where everything worked perfectly, and the result was this vibrant magenta dye. It was a real breakthrough when we finally cracked it.