The making of Ebonite

Here is a picture story about making ebonite.. I visited the factory back in 2009…

The basic recipe is quite simple, add 3% of sulfur to coutchouc (plus some other ingredients), vulcanize, and you end up with a rubber tire for your car. Adding 30% of sulfur you get ebonite, hard rubber.

A freshly delivered batch of Coutchouc. First Quality, X1, is needed to get the best results.
“Pasta” – caoutchouc after the first step, before mixing with sulfur and linseed oil. Making sure to use only the best ingredients is the best way to grant best product.
Sulfur powder, about 30% of the final product is sulfur.
The first round of ebonite production – Furs made from caoutchouc, sulfur and linseed oil.
The autoclaves will shortly be shut, then slowly heated up to 152 degress. Adding a pressure of xxx atm. will induce an exothermic reaction which vulcanizes the rubber into Ebonite.
The first round of vulcanization – caoutchouc, pure linen oil and sulfur mixed into pale yellow furs loaded into the 18 m long autoclaves.
The yellow furs now are turned into shiny black hard rubber – but this first round is only meant to be ground to ebonite powder. The second round of mixing and vulcanizing will produce the high quality hard rubber.
The black sheets crushed into particles of 3 mm diameter.
These 3mm parts are being crushed between these two large iron rolls to become Ebonite Powder. The finer the better.
these are huge…
rubber powder all over the place…
The ground hard rubber powder is now being filtered to achieve the finest possible ebonite powder. “Golden Dust” is now ready to be used for production of rods of black or colored black hard rubber.
Here is where hard rubber dust and another batch of caoutchouc is being mixed to be then made into black hard rubber.
Impressive… this has to be repeated several times to get the best result. At this point, pigments are added to color the ebonite.
The Extruder – the soft rubber mix in here is being compressed, to shape into rods, but more important – to become homogenous and absolutely free of air. A difficult task especially regarding marbled material. Slow extrusion grants perfect consistence, but to get a wonderfully marbled rod with lots of contrast it needs a speedier process.
Freshly extruded rods, still soft, ready to be pushed into the iron tubes. Every single rod diameter needs a set of tubes with diameter just a tiny bit bigger.
2 still soft red rods, which will become coral red after vulcanization. Heat pressure and sulfur attack the organic pigments – in the end, the bright colors seen here exit drastically changed. Its a magic science to know in advance, which color in the beginning produces which color in the end. On top of it – changes in extrusion tecnique, changes in climate outside – winter or summer – will always slightly vary results. This is a major difference between modern ebonite and past – Waterman boasted the use of “VERMILLON” for the production of the red ripple ebonite. Well, that is an anorganic pigment based on mercury. Nowadays, ebonite has to be “lebensmittelecht!” – kind of edible with no risk.
Soft hard rubber…
Talkum all over – every freshly extruded rod has to be covered with talkum to keep them separate.
You have to thoroughly clean the iron tubes before reloading for another round of vulcanizing.
Here you see how the agressive environment of heat and sulfur slowly reduces the machinery to rust.
6 autoclaves in a row, each 18 meters long.
This machine polishes the rough rods to precise diameter.
Stock of large diameter black hard rubber.
Colored rods…
Ebonite rods of extra large diameter – used to produce sealings in the industry. Such a rod of about 90 mm in diameter needs two rounds of vulcanization – each 72 hours. Imagine the energy needed to keep up 152 Degrees celsius for such a long period of time.
Some more colored rods. To produce Coral red is an extra challenge – the legendary coral red hard rubber of the 20ies was made using anorganic pigments – often loaded with mercury cadmium and other toxic metals. (Thus – you better not eat your Duofold Parker…) – Ebonite nowadays is made using organic fully non toxic pigments.
Its not only rods of ebonite – this polished sheet of black hard rubber can be used to produce flat product like guitar picks.
End of story…


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