Patented in 1851. Also called Vulcanite or hard rubber: a hard compound of india-rubber and sulfur
half way between true plastic materials and natural rubber. Developed by Charles Goodyear who
displayed Ebonite items in the 1851 exhibition at Crystal Palace, London. It can be any color from
black to pink (it has been used for dentures). The earlier ignition wire markers were made of Ebonite. Sometimes
the color black was specified, generally no color was stated.
Perfected in the USA in 1907 by Belgian born chemist Leo Baekeland (1863-1944).
In June 1907 he filed for a
, issued in Dec 1909,
on Bakelite, the first thermosetting phenol-formaldehyde resin. Edison used a thin layer as the sturdy recording surface
on his 1/4" thick Diamond Disc flat records in 1912; R-R
was using it for 20HP ignition wire markers by late 1921, if not before.
Ox blood was used for color in the early days when only very dark colors were available. Later
improvements were made to allow nearly any color. For ignition wire markers it was normally (dark) brown, although
some early drawings call for black Bakelite.
After its great success, bakelite became a nearly generic term for hard plastics. Some sources
even suggest that the stylized 'B' used as a Bakelite trademark (not found on wire markers) was similar to the 'Intel Inside'
logo of more modern times. You might have been able to buy generic bakelite items, but if they
carried the trademark of the Bakelite company, you had more assurance of owning the better product.
Others had worked with phenol and formaldehyde, but it was Baekeland who realized the need to
control the alkalinity of the solution and that the polymerization process could be controlled
by processing at a higher temperature (at 200C or higher) and high pressure. The physical properties
of the resulting plastic such as hardness and strength could be controlled by varying the alkalinity of the mixture.
Since we do not know the exact process details we do not know the physical
properties of the original Bakelite markers except by observing and testing existing samples. Modern day makers of similar materials, such as Sumitomo Bakelite
can, however, provide us with some general hints.
From their various material
spec sheets and other assorted data sources
we learn that modern phenolic molding compounds
have ultimate compressive strengths of 26,000-32,000 psi, Izod impact strengths of 0.28-0.34 ft-lb/in, Rockwell hardness of 110M and
maximum usage temperatures (based upon deflection tests) of 150-190C. These numbers are only guides, but give us an
indication of the properties of an original Bakelite marker.
Baekeland's US trademark for Bakelite, #75,266
, issued 14 Sept 1909, was "usually applied to the goods, or the packages containing the same...
continuously in my business since June 30, 1907." The US trademark was transferred to the Union Carbide Company
in May 1965, Georgia-Pacific Resins in 1992 and has since expired.
Synthetic Moulding Material:
Bakelite is a synthetic moulding/molding material since the base stocks used
are synthetic, carbolic acid and formaldehyde, instead of naturally occurring rubber (for Ebonite)
or milk curds (for Erinoid). Sometimes the synthetic material was 'R-R moulded', oftentimes it was 'Bought Out'.
'Synthetic moulding material' was very likely
a generic term for Bakelite since all of the ignition wire markers are made of a material that appears to be Bakelite.
The use of the Bakelite name would have been controlled by patents and trademarks
and specifying 'synthetic moulding' materials would have been less restrictive.
Strictly speaking, a semi-synthetic plastic produced by reacting casein (milk protein) with formaldehyde.
However, this is likely not the material used when the ignition wire marker drawings called for 'Erinoid'. We think the
'Erinoid' ignition wire markers were likely 'Synthetic Moulding Material' produced by the Erinoid company.
In other words, the parts were phenol-formaldehyde plastic as previously, the 'Erinoid' specification only indicated a supplier change.
Once the first of the 400 original Bakelite patents started expiring
in 1926 generic Bakelite became more available.
The Erinoid company and many other companies 'diversified into cast phenolic resins' (i.e. generic Bakelite) before WWII.
Erinoid the company seems to have produced three different materials with the tradename 'Erinoid':
casein formaldehyde, polystyrene and PVC plastics. The latter 2 weren't patented until 1930 in Germany and
the US so true Erinoid parts dating from the 20's would likely have been of the casein formaldehyde resin but by the late 30's
that would not have been a certainty. By c1980 Erinoid was a part of British Petroleum and the production
of the casein plastics was discontinued for more modern alternatives.
Casein plastics were first developed c1897 in Germany in an effort to make white chalkboard for schools. In 1913 its production
started in the UK with the Erinoid company of Lightpill, just south of Stroud, Gloucestershire.
They patented casein-formaldehyde resin as 'Erinoid' produced in various colors and often used for buttons.
British trademark #352,506 registered 10 June 1913 and US trademark #97,790
, issued 16 June 1914 (now expired), were for Erinoid
as 'A preparation of casein' first used in commerce in June 1913. Products of casein plastic were
sold under various other tradenames depending upon who made them: a long list including Galalith in Germany, Aladdinite in the US
and Lactoloid in Japan.
Museum curator websites provide information about casein plastics which differ markedly from those for Bakelite.
While Bakelite is fairly sturdy, the casein plastics are prone to water absorption, cracking and checking. One website even advises
to treat casein plastics 'as wood' for the purposes of preservation. Although details of their
production may vary from the earlier items, there are a few modern products made of casein plastics such as the Australian
Swallow knitting needles
. Swallow care instructions indicate
that if the needles are left unprotected they can 'dry out, become brittle and break easily'. Moisture 'from your hands will
eventually be absorbed into the needles and make them more flexible'. Casein-based Erinoid likely was
the material of the blind 'Cable Cuffs'
used at the ends of the primary wiring cables in pre-war distribution (fuse) boxes, switch boxes
and various other sundry locations. From the 20 HP model through the PIII and Wraith these cuffs were
always specified in various colors of Erinoid. Because they were not just dark brown or black, but white and other bright colors,
they could not have been originally made from Bakelite. And since some of the 20HP cable cuff part numbers were
still in use for the Wraith we feel the cuff materials were unchanged over all those years. The cuffs appear to be less hardy than contemporary
ignition wire markers and other Bakelite parts which helps convince us that no ignition wire markers
were made of the less sturdy, casein-based Erinoid.
Later styles of ignition wire markers differ from earlier ones only by the material specified: Erinoid
instead of 'Synthetic Moulding Material'. The later ignition wire markers of Brown Erinoid might have been either true
Erinoid (casein based) or a generic Bakelite (phenol based) produced by the Erinoid company.
Since the ignition wire markers made of 'Erinoid' appear to be 'Bakelite' and exhibit none of the casein plastic characteristics,
we believe Erinoid's phenol-based material must have been erroneously referred to in the
drawings as Erinoid; a confusion of the company name being applied
to its product. If so, it seems that such material should have been more properly labeled as
Erinite or Erinoplast, two trade names (neither trademarked in the US) supposedly used by the Erinoid company
for their phenol-formaldehyde plastics.
The drawing for part numbers E86235-40 dated 21.9.34 specified 'Bush (Ignition Wires Magneto)' to be made from 'Material A'.
They were to be engraved '1M to 6M' and filled with black enamel for use on '40/50 Tank'. It is presumed that 'A' was
aluminum. These were 0.500 x 0.400" size with a 0.364" wire ID so it is unlikely that these might be mistaken for those used on
This material was not used on any of the original markers, instead it is
the material used for the Sunset Rolls reproductions. We use a modern high strength, high temperature industrial tooling epoxy
that achieves its specified strength only after a high temperature heat treatment.
Its physical properties are roughly similar to those of modern generic bakelite: ultimate compressive strength
15,000 psi, Izod impact strength of 0.44 ft-lb/in, hardness of 88 Shore D and
maximum intermittent temperature (still strong enough for tooling purposes) of 191C.
Hardness data from different tests is difficult to compare directly, but Bakelite's Rockwell 110M is not too dissimilar
from a Rockwell 110R. Since 88 Shore D is about a Rockwell 105R, once the modern epoxy is processed, it is similar to, but not quite as hard
as the original material.
Maximum temperature is also difficult to compare directly.
How much must the material weaken, i.e. deflect under load, before a 'maximum' temperature has been reached?
Although our epoxy has a maximum specification of 191C (376F) our process includes a routine heat treatment in excess of
250C (482F). Static oven tests of original Bakelite markers as well as our epoxy indicate that both can
intermittently withstand temperatures approaching 300C(572F) with no permanent physical changes. If the markers
had to retain some level of physical strength, 191C would be an upper limit. As simply a decorative part
that has to survive mainly the force of gravity, they can withstand much higher temperatures than the ignition wires (which smoke at 200C) they adorn.
Their dark brown to black color is a natural oxidation of the epoxy that occurs only at temperatures well
in excess of those found in an operating engine compartment.
In summary, compared to Bakelite its not quite as strong or hard but also not quite as brittle, very comparable in temperature resistance
and its color does not rely upon added pigments which might fade. During the initial molding process
it also does not require the high temperatures and pressures of Bakelite avoiding many added manufacturing
headaches. We feel fortunate to have identified a material that is so similar but also amenable to low volume
production. We hope you have a chance to enjoy some of it on your car.