In pictures: Technology's hidden past

Curators and volunteers have to painstakingly clean machines such as Ernie-1 (Electronic Random Number Indicator Equipment) from 1957.

The machine was used to produce the winning numbers for the Premium Bonds, the government-sponsored lottery and savings scheme.

The machine, replaced in 1972, is cleaned with saliva and cotton buds to remove the residue left by cigarette smoke.

"That's a painting cleaning- technique," said collections care manager Marta Leskard. "Saliva is full of enzymes."