Tanks

A lot of freight went inside boxes which in turn went inside vans. The transport of bulk chemicals is quite different, as the nature of the chemical has an important impact on the wagon, and the owner has to be very clear exactly what is inside in case of emergency. The upshot is a wide variety of tank wagons on the railways of Britain.

The star on some tank wagons indicates the speed it is rated to.
One star indicates suitability for an average speed of 35 mph, and was introduced in 1913, so would be considered fast freight at the time.
Two stars appeared much later, with the advent of better technology, indicating a wagon rated up to 60 mph. I think there was also three stars for passenger rated. The system fell out of use, possibly with the introduction of data panels in the late sixties, but the stars were still visible on older wagons for some years.
Milk wagons were passenger-rated and did not carry stars

Tank wagons were classified as either class A or class B. Class A is suitable for flammable liquids, class B is not. The major difference between the two types of wagons was the arrangement of valves. Class A tanks were designed to prevent the contents leaking out if a valve is not properly closed, which means no bottom discharged – the liquid has to be pumped out. Class A wagons were pale grey with red sole bars, while class B were black.