Well, I just went out and shoveled the snow off the Salisbury axle from
681114 that has been outside behind my garage for 10 years, dragged it
in and did a bit of cleaning same as Roger and Charles have already
described, and on the cast iron center pumpkin I found remnants of both
orange-red and black paint, just as Roger predicted, but I went one
better, I took off the rear cover plate to see what color was on the
inside.
It is orange-red like the old familiar red-oxide primer, but I think Ron
had it correct first that this is really Red Glyptal or some British
equivalent, and as Dave perhaps remembered from my discussion with Kirby
Palm on this same subject many years ago on the old original jag-lovers
list, this was applied to the raw casting BEFORE any machining work was
done on it at the Salisbury factory, the idea being to seal in the
minute sand particles left in the rough surface. It is only necessary on
the inside, but I would imagine the Salisbury people or their foundry
suppliers were either generous with their spray gun or simply dunked the
whole casting in a vat, rather than spraying just the inside, so that is
why it is orange on the outside too. Roger is correct that it is
important to consider the whole manufacturing process. This would have
been done just after the casting had been cleaned in a shotblasting
cabinet, perhaps at or near the foundry, so it would not yet have been
anywhere near the oily environment of the machine shop. Charles noticed
the lack of orange on any machined surfaces, which my axle also
confirms; it is not re-applied after machining because the machining
removes enough metal that you are generally down past the sand/iron
transition region and into the good iron so you don’t need to worry
about sand from machined surfaces.
The amount of sand particles in iron casting surfaces will vary greatly
from one foundry to another, and I believe foundry practices have
improved somewhat in recent years, so the painting may have become less
necessary with some manufacturers. I believe the big USA automakers
don’t use it at all, either because they are cutting costs or because
their castings are better, I don’t know. Eastwood sells Glyptal to
engine rebuilders, touting improved oil runoff, which I suppose is a
small added benefit, but the original reason for it was sealing.
The rear cover had no paint at all on the inside. My guess based on my
experience working in manufacturing plants is that the Salisbury people
probably assembled the axle, then painted it black before shipping it to
Jaguar. I know if I had been the plant manager at Salisbury I would have
been ashamed to send out my best product to my best high profile
customer with a goofy two-tone Halloween color scheme. But they might
not have cleaned it very well before the final painting, and the glyptal
is not a good primer, that is why the black flaked off.
Speaking of archaeology, Glyptal is also used on dinosaur bones.
Rob Reilly