Lets sort of straighten a few miss ideas out there
1, cast iron brake shoes were used on engines & carriages up to the late 80's
2 , composite shoes were in use from the mid 80s or even earlier
3, composite shoes with asbestos were phased out late 80's & the composition of the shoes was changed
4, all trains had non asbestos brake shoes & no cast iron shoes from the late 80's
5 , The city underground was cleansed by staff on a special train equipped with high pressure water sprays & hoses , working late at night over many months . they may have even had a large vacume cleaner which removed the top layer first.
6 , The shiny glitter seen on platforms was from cast iron brake shoes being applied to wheels when slowing down to stop .
E & OE