The front fiddle brakes are hydraulic....
.....and are operated independently by the levers as mentioned, but the rear brakes (only) are operated by the normal footbrake pedal. Sort of like a foot operated handbrake. This is so we have a choice of turning method depending on the surface encountered.
The front brakes (both at once) are operated by the clutch pedal, which when depressed IS actually a clutch, but when depressed further operates a brake master cylinder. This means that when we want to stop quickly, we have to remember to ONLY use the front brakes as if we also try to use the rears, (other pedal) the car will spin.
We have now removed the power boosters from the system as they were leaking and we reckon we don't need them, so the system now only uses 4 master cylinders instead of 6!
Some cars in our club have used similar systems on the rear wheels on rear wheel drive cars.
As for your question "what is bitumen?".. It is the black stuff we all drive on. I believe in the U.S. it is called asphalt. Here's an excerpt from Wikipedia....
"The terms asphalt and bitumen are often used interchangeably to mean both natural and manufactured forms of the substance. In American English, asphalt (or asphalt cement) is the carefully refined residue from the distillation process of selected crude oils. Outside the United States, the product is often called bitumen."