Thread: Everything You Ever Wanted To Know About Celluloid (but was afraid to find out...)

Originally Posted by entropy1049

...Would be interesting to know just how much volume is lost during this drying process...

That's a hard one, Mike!

It seems that shrinkage is proportional to the amount of alkali present in the mix, which also introduces the other forms of Cellulose, namely the early (and dangerously explosive) cellulose nitrate which releases nitric gas during breakdown, to its safer alternatives of Cellulose biacetate, cellulose acetate and cellulose triacetate which release acetic acid and give a vinegar smell during breakdown, to a hybrid cellulose actetate nitrate. All of these would have had varying degrees of alkali within them and therefore different shrinkage rates. Shrinkage (and swelling) occur during a transitional phase, and even heat and micro-environmental differences will affect it.

Because a lot of these cellulosic plastics were used in the motion picture industry and the explosive nitrate mixtures and the corrosive acetic acid (vinegar syndrome) acetates had to be overcome, the Eastman-Kodak company ploughed a lot of research, money and man-hours into this. They came up with a water retention rate of 2 to 3 per cent for freshly made cellulosic plastics, which had to be reduced to 0.03% or under for maximum efficiency.

Part of E-As research involved chopping up preformed cellulose films or sheets (they sheet extruded cellulose up to 6inches thick) and putting this through a small bore injector with a heated barrel, heating up the pellets and effectively melting them together before they went into a screw-operated processor. Drying times in dry air (all moisture removed) and slight heating (high heat was never used in case the material deformed) was given as anything between 2 and 8 hours. However, they were making a base for film stock, which is transparent and very thin, so these drying times and possibly the processing methods themselves are not applicable to razor scales.

Which is one of the things that irritate me. people must have been trained in this and it was still in use in the 1950s and later, so we ought to know how it was done - but we do not. We know the general principles of its formation and use, but these are too broad for something as specific as razor scales. With that in mind, there were plenty of thermo-setting plastics, including the original plastic - horn, so there must have been 10s of thousands of dies, presses and moulds - where are they all now? A handful have turned up, notably in France and Solingen, but the American and British cutlery industry was enormous so one would expect at least a few presses, dies, etc to have survived, along with training manuals and old-timers first-hand experiences of using them. The devil is in the detail, and in this case both the devil and the detail are well hidden.

Regards,
Neil